Tag Archives: Le Chatelier’s principle.

Le Chatelier’s principle in your bladder

Chemistry can be so impersonal at times.  Let’s make it relevant by watching Le Chatelier’s principle at work in your bladder.

Uromodulin is the most abundant protein in your urine.  It’s a big protein with 587 amino acids with 8 sites to attach sugar chains (glycans).  It has four sites resembling epidermal growth factor, a domain rich in cysteines and two zona pellucida modules (whatever they are).

Uromodulin is produced as a GPI (GlycosylPhosphatidylInositol) precursor which is cleaved by the protease hepsin.  It then assembles into long filaments, with an average length of 25,000 Angstroms (sounds more impressive than 2.5 microns doesn’t it?)  Recall that the diameter of the hydrogen atom is 1.2 Angstroms (120 picoMeters). The filaments are shaped like a fishbone with projecting arms from a helix with a 180 degree twist and a 65 Angstrom rise.  The arm segments are 125 Angstroms long (12.5 nanoMeters) and protrude at a 45 degree angle.

E. Coli attaches to urinary tract epithelium by its needle like pili made of the protein FimH.  The pili bind to the cells lining your bladder by FimH.

Sticking out on those arms are sugar chains (glycans) particularly one linked to asparagine (Asp) at amino acid #275.

So you’ve got this long filament with 100 arms each containing a glycan.  FimH of the pili also bind here.  Now E. Coli is a cylinder 1 – 2 microns long with a diameter of .5 microns.  It’s covered with pili, all of which have 100 places to bind on the average uromodulin filament.  This clumps E. Coli together so they never get near the bladder wall.

The equilibrium binding of E. Coli pili to the bladder epithelium is disrupted by having many more sites to bind to — the equilibrium is shifted a la Le Chatelier.

The paper and editorial (Science vol. 369 pp. 917 – 918, 1005 – 1010 ’20) has some very nice pictures of the Uromodulin fiber.  They note that other glycans on uromodulin probably bind other bacteria, but this wasn’t studied in their paper.

How little we know

Well it’s basic biochem 101, but enzymes only allow equilibrium to be reached faster (by lowering activation energy), they never change it. This came as a shock to the authors of [ Proc. Natl. Acad. Sci. vol. 112 pp. 6601 – 6606 ’15 ] when Cytosolic Nonspecific DiPeptidase 2 (CNDP2), a proteolytic enzyme, was found to tack the carboxyl group of lactic acid onto the amino group of a variety of amino acids, essentially running the proteolytic reaction in reverse. Why? Because intracellular levels of lactic acid and amino acids are in the high microMolar to milliMolar range. It’s Le Chatelier’s principle in action.

The compounds are called N-Lactoyl amino acids. No one had ever seen them before. They are part of the ‘metabolome’ — small molecules found in our bodies. God knows what they do. The paper was really shocking to me for another reason, because I had no idea how many members the metabolome has.

How large is the metabolome? Make a guess.

Well METLIN (https://metlin.scripps.edu/index.php has 240,000, and Human Metabolome DataBase http://www.hmdb.ca/metabolites?c=hmdb_id&d=up&page=1676 has 42,000. I doubt that we know what they are all doing. Undoubtedly some of them are binding to proteins producing physiologic effects. Drug chemists may be mimicking some of them unknowingly, producing untoward and unexpected side effects.

What’s even more shocking to me is the following statement from the paper. State of the art untargeted metabolomics studies still report ‘up to’ 40% unidentified, but potentially important metabolitcs which can be detected reproducibly. The unknown metabolites are only rarely characterized because of the extensive work required for de novo structure determination..

So we really don’t know everything that’s out there in our bodies, and even if we did, we don’t know what they are doing. Drug discovery is hard because we only dimly understand the system we are trying to manipulate. Until I read this paper, I had no idea just how dim this is.