Do glia think? Take II

Do glia think Dr. Gonatas?  This was part of an exchange between G. Milton Shy, head of neurology at Penn, and Nick Gonatas a brilliant neuropathologist who worked with Shy as the two of them described new disease after new disease in the 60s ( myotubular (centronuclear) myopathy, nemaline myopathy, mitochondrial myopathy and oculopharyngeal muscular dystrophy).

Gonatas was claiming that a small glial tumor caused a marked behavioral disturbance, and Shy was demurring.  Just after I graduated, the Texas Tower shooting brought the question back up in force — https://en.wikipedia.org/wiki/University_of_Texas_tower_shooting.

Well that was 55 years ago, and we’ve learned a lot more about glia since.  

If glia don’t actually think, they may actually help neurons think better.  Since the brain is consuming 20% of your cardiac output as you sit there, it had better use the energy in the form of glucose  brought to it efficiently, and so it does, oxidizing it using oxygen (aerobic metabolism).  Glia on the other hand for reasons as yet unknown oxidize glucose anaerobically producing lactic acid (aerobic glycolysis). They transport the lactic acid to neurons and blocking transport impairs memory consolidation in experimental animals.  In fact aerobic glycolysis occurs in conditions of high synaptic plasticity and remodeling.  

The brain is 60% fat, some of which is cholesterol, which has to be made in the brain, as it doesn’t cross the blood brain barrier. Although neurons can synthesize cholesterol from scratch, most synthesis of cholesterol in the brain occurs in astrocytes.  It is than carried to neurons by apolipoprotein E.  As you are doubtless aware, apolipoprotein E (APOE) comes in three flavors 2, 3 and 4, and having two copies of APOE4 increases your risk of Alzheimer’s disease. 

But APOE does much more than schlep cholesterol to neurons according to a recent paper [ Neuron vol. 109 pp. 907 – 909, 957 – 970 ’21 ] Inside the particles are microRNAs.  You’ll recall that microRNAs decrease  the expression of proteins they target by binding to the messenger RNA (mRNA) for the targeted protein triggering its destruction. 

The microRNAs inside APOE suppress enzymes involved in de novo neuronal cholesterol biosynthesis (why work making cholesterol when the astrocyte is giving to you for free?).

This is unprecedented.  Passing metabolites (lactic acid, cholesterol) to neurons is one thing, but changing neuronal protein expression is quite another. 

Passing microRNAs in exosomes has been well worked out between cells (particularly cancer cells) outside the brain, but that’s for another time. 

Welcome to the world of the physician

In a sense, the uncertainty about hematologic complications of the pandemic vaccines is good in that it is a real teaching moment for the public about what docs confront every day — balancing risk vs. reward. 

No drug is without side effects.  No surgery is without complications.  It is good to see the public  wrestle with these things.  

For a very good explanation of what those complications are and the risks and rewards of taking the vaccines please see — 

https://blogs.sciencemag.org/pipeline/archives/2021/04/14/vaccine-side-effects-q-and-a

Even more interesting are the 139 comments found at the end of  the article.  Some are from experts, some are from frightened lay people; as always there are people with an ax to grind.  As is usually the case in medicine, the data are not clear cut and sometimes contradictory.  As is always the case more data would be helpful, is desired and rarely available.  What is particularly interesting to me is the way some very knowledgable people wrestle with the data, interpreting the same data differently.  Welcome to the real world. 

On a more positive note, a friend who teaches at Hopkins sent me the a copy of the eMail below, with permission to share it.  This provides lots of excellent data on the protective effects of vaccination in a  group of people with a fairly high risk of exposure to the virus,  working at a major medical center where lots of very sick COVID-19 patients are being treated. 

35,000 were vaccinated.  Nonetheless 51 became infected at a time of maximum protection (5 weeks or more after the first shot), demonstrating that the vaccine isn’t 100% protective.  But no one ever claimed that it was.

 But only 2 of the 51 required hospitalization.  So the vaccine is effective in preventing serious illness from the virus (2/35,000).  So who cares if the other 49 had the symptoms of the flu.  They don’t and you shouldn’t.  The number of hematologic complications wasn’t stated. There were two at most, as they always result in hospitalization.  

To the Johns Hopkins Medicine community   Dear Colleagues,   As we continue to monitor COVID-19 infection and vaccination trends at Johns Hopkins Medicine (JHM), we want to share some data about the incidence of infection among JHM personnel following partial and full vaccination.   You are considered fully vaccinated, per the Centers for Disease Control and Prevention, two weeks or more after receiving the second dose of a two-dose COVID-19 vaccine regimen and two weeks or more after receiving a one-dose COVID-19 vaccine regimen. This is when the body has had a chance to produce the antibodies and immune response that protect against infection. Before this time, if you have started the vaccination series, you are considered partially vaccinated and you do not yet have the full amount of protection the vaccination provides against infection. While full vaccination has been found to be highly effective at preventing COVID-19, infection (the incidence is very low) is still possible even after being fully vaccinated.   We are monitoring the situation to determine how often infection seems to occur after partial or full vaccination, and the severity of those infections.   As of April 12, 2021, of the nearly 35,000 employees who were fully vaccinated (14 days or more after a second dose), 51 employees (0.14% of those who have been fully vaccinated) had tested positive for COVID-19. This demonstrates that SARS-CoV-2 infection is possible even after full vaccination, and it highlights the importance of continuing to practice basic infection prevention precautions after full vaccination. The good news is that acquiring COVID-19 after full vaccination appears to be relatively rare and, among these 51 cases, only two were severe enough to require hospitalization. This shows that the COVID-19 vaccine is highly protective against severe disease, hospitalization and death. If you have not yet been vaccinated, please schedule your appointment as soon as you can to protect yourself and others.

Some very disturbing pictures

Granted that these pictures look like microscope slides containing colored blobs, but once you understand what they show, the implications are quite frightening.

These images are biopsies of various portions of the gastrointestinal tract in a person who had become  symptomatic  three months earlier with COVID-19 from which the person  has now recovered).The green blobs represent fluorescent antibodies binding to the nucleocapsid protein of the pandemic virus (SARS-CoV-2).  They are found in the enterocyte cells which line the inside of the gut.  These are the enterocyte which live for just 5 days before they are shed.  

This is my first shot at getting pictures into my blog, and they do appear blurry (apologies !).  I will try to correct this. All you need view is in the first and second columns of rows a, c, and e as most  of the rest are controls. The pictures are from a Nature paper — here’s a link — https://www.nature.com/articles/s41586-021-03207-w.pdf

 

Why is this disturbing?  Because their presence implies that they have been made continually for the whole three months, as enterocytes are born and die. 

Well maybe it’s an artifact confined to one patient.  Unfortunately similar findings were present in 5/14 cases recovered COVID-19 patients who received GI tract biopsies for clinical reasons unrelated to COVID-19.  The 14 are from a larger series of recovered COVID19 patients (see the copy of the previous post below). Like Reverend Paley’s found watch, the presence of the viral nucleocapsid protein demands an explanation of what had to be present to put it there.

There are a series of requirement for this to happen.  The messenger RNA for the protein had to be made and present, which, in turn means at the least that the viral gene from which the mRNA for the nucleocapsid protein was made must also be present.  What mades nucleocapsid mRNA? The viral RNA dependent polymerase. So the polymerase must be present as well, along with the 3 genes coding for the 3 proteins making up the polymerase.  Not only that but all of the above must have been present in longer lived cells  than the enterocytes.

Defective viruses certainly appear during the course of viral infection (particularly as in AIDS), but it is very scary to realize just how much of the virus must be present and functioning to produce just these findings. Perhaps the fluorescent antibody was really binding to another protein, not from the virus at all.  After all, antibodies aren’t always as specific as we’d like them to be.  

However, the authors did something else which makes this much less likely. They wrote, “In addition, viral RNA was detected by in situ hybridization in biopsy samples from the two participants who were tested for it”

Further scariness:  Pictures e and f show the nucleocapsid protein is present at the far end of the terminal ileum (small intestine) a part of our GI tract which is 22 feet long. 

So this person although well, was literally crawling with both the viral protein and the machinery necessary to make it. 

Are many more, or all such people who are clinically recovered from clinical COVID-19 excreting infectious virus?  I’m sure people have looked, and if they haven’t they should be. 

I’m going to now insert the previous post on the subject.  It contains a link to the Nature paper, so feel free to follow it and look for yourself.  It contains a lot more detail. 

Is the virus still within you? Will it cause trouble?

Let’s say you’ve recovered from a bout with COVID-19. Is the virus still with you? Could it come back and cause trouble? Given the data in a recent paper [ Nature vol. 591 pp. 639 – 644 ’21 ] — https://www.nature.com/articles/s41586-021-03207-w.pdf, it’s quite possible.

But first a story about my grandmother.  She was born somewhere around the Baltic Sea in 1880 and came to America in 1893.  She died of undiagnosed (hence untreated) miliary Tuberculosis in a University Hospital in 1967.  Just about everyone in Europe in the 1880s was exposed to TB and just like SARS-CoV-2 many if not most were asymptomatic.  Their lungs walled off the organism in something called a Gohn complex — https://en.wikipedia.org/wiki/Ghon%27s_complex.  The organism didn’t die — and probably broke out of the complex as my grandmother aged and her immune system got weaker and weaker.  It is very unlikely that she picked it up by exposure in the 1960’s.  As they say TB is forgotten but not gone.  

Which brings me to the Nature paper.  At first I thought it was great and very optimistic.  Some 87 people from New York City who had symptomatic SARS-CoV-2 infection (proven by finding the viral genome using RT-PCR technique).  The authors studied the antibody responses at an average of 1.3 and 6.2 months after infection.  Although the antibody levels dropped (which always happens) they changed so they bound the virus more tightly.  This is called affinity maturation — https://en.wikipedia.org/wiki/Affinity_maturation.  

So that’s good? 

No that’s bad because it implies that the protein stimulating affinity maturation is still around. The authors note the persistent antigenic stimulation of the immune system is possible because an “antigen trapped in the form of immune complexes on follicular dendritic cells .. . . . can be long-lived, because follicular dendritic cells do not internalize immune complexes”.  

Well maybe, but the paper gives evidence for another mechanism of antigen persistence (which I find more persuasive). 14 of the people had intestinal biopsies for appropriate clinical indications (see Table 7 in the supplementary information of the article). In some of the biopsies they detect viral antigen in some of the enterocytes (cells which line the inside of the gut) — I’m assuming the antigen is the viral spike protein, but it’s hard to find exactly what it is. 

This is quite bad, as the lifetime of the enterocyte is 5 days.  This means that the antigen is being continually produced, which means that the mRNA for the antigen is being continually produced, which in turn means that the viral genome is still around.  The mean lifetime of cellular mRNAs is 10 hours although some hang around for days, however I doubt that the mRNA responsible for the viral antigen had lasted for 2.8 to 5.7 months which is the time after clinical infection when the biopsies were done. 

So it is possible, that like TB in the Gohn complex, the immune system has fought the virus to a draw, but that the intact organism could be still present.  As in my grandmother, it is possible that the virus will reappear as the immune system weakens with age (something that happens in all of us). 

In that case we wouldl have recrudescence not reinfection. 

PS:  My grandmother came to this country at age 13 alone and speaking no English.  Every time I feel sad at what the pandemic has put us all through, I think of that generation.  

PPS: When she got sick, I wanted to put her in the hospital where I was an intern, but our family GP (Dr. Richard A. Gove) told me taking care of my own family was a very bad idea and put her elsewhere.  I doubt that I’d have made the diagnosis, or that anyone at our hospital would have. 

PPPS:  I don’t know if they still do autopsies, but I was always able to get one after I’d tell families of the deceased about my grandmother.  It meant that my wife and I and our two little kids were all screened for TB. 

PPPPS — a friend brought up the following — Eleanor Roosevelt, who was thought to have aplastic anemia, was treated with prednisone and later found to have died of military tuberculous, probably the recurrence of tb acquired some 4 decades earlier.

 

 

Is the virus still within you? Will it cause trouble?

Let’s say you’ve recovered from a bout with COVID-19. Is the virus still with you? Could it come back and cause trouble? Given the data in a recent paper [ Nature vol. 591 pp. 639 – 644 ’21 ] — https://www.nature.com/articles/s41586-021-03207-w.pdf, it’s quite possible.

But first a story about my grandmother.  She was born somewhere around the Baltic Sea in 1880 and came to America in 1893.  She died of undiagnosed (hence untreated) miliary Tuberculosis in a University Hospital in 1967.  Just about everyone in Europe in the 1880s was exposed to TB and just like SARS-CoV-2 many if not most were asymptomatic.  Their lungs walled off the organism in something called a Gohn complex — https://en.wikipedia.org/wiki/Ghon%27s_complex.  The organism didn’t die — and probably broke out of the complex as my grandmother aged and her immune system got weaker and weaker.  It is very unlikely that she picked it up by exposure in the 1960’s.  As they say TB is forgotten but not gone.  

Which brings me to the Nature paper.  At first I thought it was great and very optimistic.  Some 87 people from New York City who had symptomatic SARS-CoV-2 infection (proven by finding the viral genome using RT-PCR technique).  The authors studied the antibody responses at an average of 1.3 and 6.2 months after infection.  Although the antibody levels dropped (which always happens) they changed so they bound the virus more tightly.  This is called affinity maturation — https://en.wikipedia.org/wiki/Affinity_maturation.  

So that’s good? 

No that’s bad because it implies that the protein stimulating affinity maturation is still around. The authors note the persistent antigenic stimulation of the immune system is possible because an “antigen trapped in the form of immune complexes on follicular dendritic cells .. . . . can be long-lived, because follicular dendritic cells do not internalize immune complexes”.  

Well maybe, but the paper gives evidence for another mechanism of antigen persistence (which I find more persuasive). 14 of the people had intestinal biopsies for appropriate clinical indications (see Table 7 in the supplementary information of the article). In some of the biopsies they detect viral antigen in some of the enterocytes (cells which line the inside of the gut) — I’m assuming the antigen is the viral spike protein, but it’s hard to find exactly what it is. 

This is quite bad, as the lifetime of the enterocyte is 5 days.  This means that the antigen is being continually produced, which means that the mRNA for the antigen is being continually produced, which in turn means that the viral genome is still around.  The mean lifetime of cellular mRNAs is 10 hours although some hang around for days, however I doubt that the mRNA responsible for the viral antigen had lasted for 2.8 to 5.7 months which is the time after clinical infection when the biopsies were done. 

So it is possible, that like TB in the Gohn complex, the immune system has fought the virus to a draw, but that the intact organism could be still present.  As in my grandmother, it is possible that the virus will reappear as the immune system weakens with age (something that happens in all of us). 

In that case we wouldl have recrudescence not reinfection. 

PS:  My grandmother came to this country at age 13 alone and speaking no English.  Every time I feel sad at what the pandemic has put us all through, I think of that generation.  

PPS: When she got sick, I wanted to put her in the hospital where I was an intern, but our family GP (Dr. Richard A. Gove) told me taking care of my own family was a very bad idea and put her elsewhere.  I doubt that I’d have made the diagnosis, or that anyone at our hospital would have. 

PPPS:  I don’t know if they still do autopsies, but I was always able to get one after I’d tell families of the deceased about my grandmother.  It meant that my wife and I and our two little kids were all screened for TB. 

PPPPS — a friend brought up the following — Eleanor Roosevelt, who was thought to have aplastic anemia, was treated with prednisone and later found to have died of military tuberculous, probably the recurrence of tb acquired some 4 decades earlier.

 

 

 

Minorities on course to win the Darwin awards

While the plural of anecdote is not data, two episodes this week have me very depressed about the spread of the pandemic virus in the minority community (particularly in Blacks). The first occurred with a very intelligent Black woman who worked in tech support at Comcast and helped us when our internet connection went down. You do not get a job like that unless you’re smart. She’s heard a lot about vaccine side effects and isn’t going to get it. The next was a National Guard woman working for AAA, who won’t get the vaccine unless its a military requirement.

At 3 visits to our vaccination site in a town 45% of the population is Puerto Rican we saw nary a one (except for the guy disinfecting the chairs). I talked to one of the nurses, who said that our experience is typical of what she sees day after day.

One way to make a dent in this, is force hospitals when reporting COVID19 deaths, to state whether the patient was vaccinated or not. Granted most COVID19 will not be vaccinated at out current levels of vaccination, but as this doesn’t change with increasing vaccination levels, perhaps they will be convinced (but unfortunately after a lot of unnecessary deaths.

This is not written with the old WordPress Editor, but with the new one which I hate. It doesn’t seem to let you put in tabs.

You now have to pay up to get Premium edition to install the classic editor. Although initially angered, I’ve been using it for a decade absolutely free, and it’s time to pay up

More moonlighting

Well we used to think we understood what ion channels in the cell membrane did and how they worked. To a significant extent we do know how they conduct ions, permitting some and keeping others out in response to changes in membrane potential and neurotransmitters. It’s when they start doing other things that we begin to realize that we’re not in Kansas anymore.

Abnormal binding of one protein (filamin A) to one of the classic ion channels (the alpha7 nicotinic cholinergic receptor) may actually lead to a therapy for Alzheimer’s disease — for details please see — https://luysii.wordpress.com/2021/03/25/the-science-behind-cassava-sciences-sava/

The Kv3.3 voltage gating potassium channel is widely expressed in the brain.  Large amounts are found neurons concerned with sound, where firing rates are high.  Kv3.3 repolarizes them (and quickly) so they can fire again in response to high frequency stimuli (e.g. sound).  Kv3.3 is also found in the cerebellum and a mutation Glycine #529 –> Arginine is associated with a hereditary disease causing incoordination (type 13 spinocerebellar ataxia or SCA13 to be exact).

Amazingly the mutant conducts potassium ions quite normally.  The mutation (G529R) causes the channel not to bind to something called Arp2/3 with the result that actin (a muscle protein but found in just about every cell in the body) doesn’t form the network it usually does  at the synapse.  Synapses don’t work normally when this happens. 

Why abnormally functioning synapses isn’t lethal is anyone’s guess, as is why the mutation only affects the cerebellum.  So it’s another function of an ion channel, completely unrelated to its ability to conduct ions (e.g. moonlighting). 

The science behind Cassava Sciences (SAVA)

I certainly hope Cassava Sciences new drug Sumifilam for Alzheimer’s disease works for several reasons

l. It represents a new approach to Alzheimer’s not involving getting rid of the plaque which has failed miserably

2. The disease is terrible and I’ve watched it destroy patients, family members and friends

3. I’ve known one of the principals (Lindsay Burns) of Cassava since she was a teenager and success couldn’t happen to a nicer person. For details please see https://luysii.wordpress.com/2021/02/02/montana-girl-does-good-real-good/.

Unfortunately even if Sumifilam works I doubt that it will be widely used because of the side effects (unknown at present) it is very likely to cause.  I certainly hope I’m wrong.

Here is the science behind the drug.  We’ll start with the protein the drug is supposed to affect — filamin A, a very large protein (2,603 amino acids to be exact).  I’ve known about it for years because it crosslinks actin in muscle, and I read everything I could about it, starting back in the day when I ran a muscular dystrophy clinic in Montana.  

Filamin binds actin by its amino terminal domain.  It forms a dimerization domain at its carboxy terminal end.  In between are 23 repeats of 96 amino acids which resemble immunoglobulin — forming a rod 800 Angstroms long.  The dimer forms a V with the actin binding domain at the two tips of the V, making it clear how it could link actin filaments together. 

Immunoglobulins are good at binding things and Lindsay knows of 90 different proteins filamin A binds to.  This is an enormous potential source of trouble.  

As one might imagine, filamin A could have a lot of conformations in addition to the V, and the pictures shown in https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2099194/.

One such altered (from the V) conformation binds to the alpha7 nicotinic cholinergic receptor on the surface of neurons and Toll-Like Receptor 4 (TLR4) inside the cell.

Abeta42, the toxic peptide, has been known for years to bind tightly to the alpha7 nicotinic receptor — they say in the femtoMolar (10^-15 Molar) range, although I have my doubts as to whether such tiny concentration values are meaningful.  Let’s just say the binding is tight. 

The altered conformation of filamin A makes the binding of Abeta to alpha7even tighter. 

In some way, the tight binding causes signaling inside the cell (mechanism unspecified) to hyperphosphorylate the tau protein, which is more directly correlated with dementia in Alzheimer’s disease than the number of senile plaques. 

So what does Sumifilam actually do — it changes the ‘altered’ conformation of filamin A back to normal, decreasing Abeta signaling inside the cell.  

How do they know the conformation of filamin A has changed?  They haven’t done cryoEM or Xray crystallography on the protein.  The only evidence for a change in conformation, is a change in the electrophoretic mobility (which is pretty good evidence, but I’d like to know what conformation is changed to what).

Notice just how radical this proposed mechanism of action actually is.  The nicotinic cholinergic receptor is an ion channel, yet somehow the effect of Sumifilam is on how the channel binds to another protein, rather than how it conducts ions. 

However they have obtained some decent results with the drug in a very carefully done (though small — 13 patients) study in J. Prev Alz. Dis. 2020 (http://dx.doi.org/10.14283/ipad2020.6) and the FDA this year has given the company the go ahead for a larger phase III trial.

Addendum 26 March: The above link didn’t work.  This one should — it’s from Lindsay herself

https://link.springer.com/article/10.14283/jpad.2020.6

Why, despite rooting for the company and Lindsay am I doubtful that the drug will find wide use.  We are altering the conformation of a protein which interacts with at least 90 other proteins (Lindsay Burns, Personal Communication).  It seems inconceivable that there won’t be other effects in the neuron (or elsewhere in the body) due to changes in the interaction with the other 89 proteins filaminA interacts with.  Some of them are likely to be toxic. 

To understand anything in the cell you need to understand nearly everything in the cell

Understanding how variants in one protein can either increase or decrease the risk of Parkinson’s disease requires understanding of the following: the lysosome, TMEM175, Protein kinase B, protein moonlighting, ion channel lysoK_GF, dopamine neurons among other things. So get ready for a deep dive into molecular and cellular biology.

It is now 50 years and 6 months since L-DOPA was released in the USA for Parkinson’s disease, and I was tasked as a resident by the chief with running the first L-DOPA clinic at the University of Colorado.  We are still learning about the disease as the following paper Nature vol. 591 pp. 431 – 437 ’21 will show. 

The paper describes an potassium conducting ion channel in the lysosomal membrane called LysoK_GF.  The channel is made from two proteins TMEM175 and protein kinase B (also known as AKT).

TMEM175 is an ion channel conducting potassium.  It is unlike any of the 80 or so known potassium channels.  It  contains two repeats of 6 transmembrane helices (rather than 4) and no pore loop containing the GYG potassium channel signature sequence. Lysosomes lacking it aren’t as acidic as they should be (enzymes inside the lysosome work best at acid pH).  Why loss of a potassium channel show affect lysosomal pH is a mystery (to me at least).

Genome Wide Association Studies (GWAS) have pointed to the genomic region containing TMEM175 as having risk factors for Parkinsonism.  Some variants in TMEM175 are associated with increased risk of the disease and others are associated with decreased risk — something fascinating as knowledge here should certainly tell us something about Parkinsonism.  

The other protein making up LysoK_GF is protein kinase B (also known as AKT). It is found inside the cell, sometimes associated with membranes, sometimes free in the cytoplasm. It is big containing 481 amino acids. Control of its activity is important, and Cell vol. 169 pp. 381 – 405 ’17 lists 21 separate amino acids which can be modified by such things as acetylation, phosphorylation, sumoylation, Nacetyl glucosamine, proline hydroxylation.  Well 2^21 is 2,097,152, so this should keep cell biologists busy for some time. Not only that some 100 different proteins AKT phosphorylates were known as 2017.  

TMEM175 is opened by conformational changes in AKT.  Normally the enzyme is inactive because the pleckstrin homology domain binds to the catalytic domain inhibiting enzyme activity as the substrate can’t get in.

Remarkably you can make a catalytically dead AKT, and it still works as a controller of TMEM175 activity — this is an example of a moonlighting molecule — for more please see — https://luysii.wordpress.com/2021/01/11/moonlighting-molecules/.

Normally the activity and conformation of AKT is controlled by the metabolic state of the cell (with 21 different molecular knob sites on the protein this shouldn’t be hard).  So the fact that AKT conformation controls TMEM175 conductivity which controls lysosome activity gives the metabolic state of the cell a way to control lysosomal function.  

Notice how to understand anything in the cell you must ask ‘what’s it for’, thinking that is inherently teleological. 

Now on to the two risk factors for Parkinsonism in TMEM175.  The methionine –> threonine mutation at amino acid #393 reduces the lysoK_GF current and is associated with an increased risk of parkinsonism, while the glutamine –> proline mutation at amino acid position #65 gives a channel which remains functional under conditions of nutrient starvation. 

The authors cultured dopamine neurons and found out that the full blooded channel LysoK_GF (TMEM175 + AKT) protected neurons against a variety of insults (MPTP — a known dopamine neuron toxin, hydrogen peroxide, nutrient starvation). 

TMEM175 knockout neurons accumulate more alpha-synuclein — the main constituent of the Lewy body of Parkinsonism.

So it’s all one glorious tangle, but it isn’t just molecular biological navel gazing, because it is getting close to one cause (and hopefully a treatment) of Parkinson’s disease.  

The pandemic virus as evolution professor

Like it or not, the pandemic virus (SARS-CoV-2) is giving us all lessons in evolution and natural selection. The latest is one of the clearest examples of natural selection you are likely to see.  It is very clear cut, but to leave almost no one behind, I’m going to put in a lot of background material which will bore the cognoscenti — they can skip all this and go to the meat of the issue after the ****

The genetic code is read in groups of 3.  Imagine a language in which all words must be 3 letters long. 

The dog ate the fat cat who bit the toe off one mad rat.   Call this the reading frame, in which the words all make sense to you

Any combination of 3 letters means something to the machinery inside the cell responsible for reading the code, so deleting the f in fat 

gives us 

The dog ate the atc atw hob itt het oeo ffo nem adr at.   So this is a shift of 1 from the reading frame.  While it may not make sense to you, it makes sense to the cellular machinery. 

Now let’s delete 2 letters (in a row)

The dog ate the fat cat who bit the tof fon ema dra t.  

Not much sense after the deletion is there?  Or at least a completely different message.  This is a shift of 2 from the reading frame.

Now 3 letters (in a row)

The dog ate the fat cat who bit the toe off one mad rat.  

This gives 

The dog ate the fat cat who bit the tff one mad rat.  

Which has a funny looking word (tff), but leaves the rest of the 3 letter words intact (one mad rat).  This is called an in frame deletion. It basically lops out a single 3 letter word.  

Lopping out 4, 5, 6, .. letters will just give you one of the 3 patterns (frame shift of 1, frame shift of 2 or no frameshift at all) shown above (but nothing new)

*****

Now the business end of the pandemic virus is the spike protein, and these are where the mutations everyone is worried about occur.  The spike protein binds to another protein (ACE2) on the surface of human cells and then the virus enters causing havoc.  All the vaccines we have are against the spike protein. 

The spike protein is big (1,273 different 3 letter words).  

Mutations occur randomly.  We now have something called GISAID (Global Initiative on Sharing All Influenza Data) which has well over 100,000 genome sequences of the virus.  

Other things being equal we should see as many 1,  4 (3+1), 7 (2*[3] + 1), 10 letter deletions as 2, 5 (3 + 2), 8 ( 2*[3] + 2) , as 3, 6, 9, 12, letter   deletions.

The set  1, 4, 7, 10, . . represents a shift of 1 from the original reading frame, the set 2, 5, 8, 11 … represents a frame shift of two and 3, 6, 9 .. represents a set of deletions producing no frameshift at all.

Since thousands on thousands of experiments show that mutations occur randomly, 1/3 of all deletion mutations should show a frameshift of 1, 1/3 of all deletion mutations should have a frame shift of 2, and 1/3 of all deletion mutations should produce no frameshift at all. 

Well the authors of Science vol. 371 pp. 1139 – 1142 ’21  looked at 146,795 viral sequences and found 1,108 deletions in the gene for the spike protein.

They did not find each of the 3 types of deletions occuring to the same extent (1/3 of the time).  Among all deletions, 93% were in frame.  

Why? Because out of frame deletions change everything that comes after them. 

Recall

The dog ate the atc atw hob itt het oeo ffo nem adr at.  

This means that a functional spike protein won’t be formed, and the virus won’t infect our  cells, and it certainly won’t be found in GISAID.  

Ladies and Gentlemen you have just witnessed natural selection in action. 

Actually it’s even more complicated and even more impressive than that.  The in frame deletions occurred in one of four areas, which happen to be where antibodies to the spike protein bind.  So the out of frame deletions were selected against, and the in frame deletions were selected for. 

The blind watchmaker in action.

Another way to see how improbable it is that random choice should choose one of 3 equally probable possibilities 97% of the time, imagine that you are throwing dice.  You throw a single dye 100 times, and 97 times you get either of two numbers (say 3 and 6) .  You know the dye is loaded.  The load being natural selection in the case of genome deletions. 

 

 

 

 

 

Answer to Friday’s homework problem

2 days ago you were tasked with the following homework problem: Design a protein to capture cholesterol and triglycerides and insert them between the two leaflets of the standard biological membrane similar but not identical to the plasma membrane.

Why not just tell you Nature/God/Evolution’s solution to the problem?  Because unless you’ve thought about how you’d do it, you won’t appreciate the elegance (and beauty to a chemist) of the solution. 

Lipid droplets are how your cells store cholesterol and triglycerides (neutral fats).  Cholesterol and most fats are made in the lumen of the endoplasmic reticulum.  Then they move through the homework protein and accumulate between the two leaflets of the endoplasmic reticulum membrane, growing into lens-like structures with diameters of 400 to 600 Angstroms before they leave to enter the cytoplasm.  

Well clearly to get them between the sheets so to speak a hole must be formed in the membrane leaflet closest to the lumen, and the hole must have open sides so the cholesterol and triglyceride can escape.  

The protein must also catch the lipids in the lumen.  This is accomplished by an 8 stranded beta sandwich.  The protein must also cross the endoplasmic reticulum membrane so the lipids its caught can escape the sides.  

Like a lot of pores in the membrane (such as ion channels), several copies of the protein must come together to form the hole.  In this case the protein contains two transmembrane alpha helices.  Its hard to count just how many monomers make up the power, but my guess is 11 or so. 

Here’s a picture

 

The transmembrane (TM)alpha helices are in purple, the beta sandwiches are in blue-greem.

8 nm is 8 nanoMeters or 800 angstroms.  The hole looks to be around 30 Angstroms across — plenty of room to allow cholesterol and triglycerides to enter.  When you look at the top view you see that there is plenty of room between the alpha helices within the membrane for the lipids to escape out the side.  

Here’s the reference https://www.pnas.org/content/pnas/118/10/e2017205118.full.pdf

and the citation Proc. Natl. Acad. Sci. vol. 118 pp. e2017205118 ’21.  It’s a beautiful paper

The protein itself is called seipin, and mutations cause a variety of lipodystrophies, some of which have mental retardation.  The paper has some nice molecular dynamics simulations of seipin in action (if you believe that sort of thing). 

Were you smart enough to figure all this out on your own.  Nature/God/Evolution was.  I wasn’t.