The diversity of functional groups on sugars that can form glycosidic bonds greatly increases the information content of glycans relative to oligopeptides

Question

(A) Consider three amino acids, A, B, and C. How many tripeptides can be formed from one molecule of each amino acid?

(B) Now consider three sugars—glucose, glucuronic acid, and N-acetylglucosamine. Use shorthand (e.g., Glcα(1 → 4)GlcUAβ(1 → 4)GlcNAc to represent ONLY 10 trisaccharides with the sequence Glc-GlcUA-GluNAc. Is your list exhaustive? Note: consider the combination of a/b and linkages (not limited to 1( 4 (can be 1 ( 2, 1(3, 1 ( 6) etc

Answer 1

Hi Nicole L.,

If you examine the cyclic structures for the three glycans there, the first 2 have 5 attachment points, and the N-acetylglucosamine has 4 attachment points. So you'd have to consider the two types of linear linkage: 5-er -> 5-er -> 4-er and 5-er-> 4-er -> 5-er separately, I think. The former would have 2 orders, and (5*5)*(4*4) attachments within that; the latter would have (5*4)*(3*5) attachments, but that would include ordering in either direction. So that's 800 + 300 = 1100 possibilities. I'd imagine that if you cooked up a witches' brew of random orders, etc. and "sprinkled" it onto human albumin, for example, and injected (or administered dermally in DMSO), you might induce potent autoimmune responses in humans. (Don't even think about it!) But if this same material (or appropriate equivalent) were administed into a plant, for example, from whence it was imbibed by a parasite, perhaps that same autoimmune response could be usefully triggered in said parasite, killing it. Now you're talking commercial potential!

-- Cheers, -- Mr. d.