Ph has a major influence on protein structure by altering electrostatic interactions. in order to illustrate this point, let us think about polylysine (a polypeptide chain consisting of only l-lysine residues). at ph 10 and above, polylysine forms an ahelix. at a ph of 7 and below, however, this same polypeptide chain assumes an unfolded conformation (often referred to as ‘random coil’ or ‘random conformation’).

1) can you explain why this transition occurs at phs below the pka of lys?

2) what other residue(s) might you expect to show a similar pattern of ph-dependent folding and unfolding?

3) the residue(s) you might expect based on charge to be capable of forming α-helices do not do so in water when they alone make up a polypeptide chain. can you come up with a reasonable explanation for why this might be?

4) speculate on what you think might happen to the ph-dependence of α-helix formation if you had a polypeptide chain consisting of both glutamate and lysine residues.