Polyproline ordered conformation

In 1959, C. G. Overberger initiated a program to study various parameters which influenced the ordered conformation of polyproline type pol)nners the results demonstrate that substitution of a methyl group at the 2-posltion, poly-2-methylproline (P2MP), can perturb the conformation of the polymeric chains so that the resultant poljnner no longer behaves like a typical poly-L-proline system. However, substitution of a methyl group at the 5-position (cis- and trans-) resulted in only a small modification of... 

In addition to the order-disorder transition, observed for a helices, helical structures can also be induced to undergo transitions from one ordered form to another. For example, a crystalline form of poly[p-(p-chlorobenzyl)-L-aspartate] can be made to undergo a phase transition from an a-helical to an co-helical form by heating rotational entropy is computed to play a role in this process.68 Another order-order transition is the solvent-induced interconversion between polyproline 1 (with cis peptide bonds) and polyproline 11 (with trans peptide bonds), a process that has also been subjected to conformational energy calculations.85 The transition has been accounted for in terms of differences in the binding of solvent components to the peptide 0=0 groups. 

Pi positions) is more twisted than a regular /3-strand to possess the polyproline II (PPII) helix conformation. The PPII conformation is also frequently used in protein-peptide interactions such as those seen in the peptide recognition by SH3 domains (Lim et at, 1994) and class II MHC molecules (Stem et at, 1994). This conformation allows the peptide chain to twist in order to maximize the interaction of its side chains with a protein surface. As a consequence, large proportions of the side chains at the P 2 Po 3.nd Pi positions of the receptor peptides are buried at the TRAF2 interface. Therefore, in the case of TRAF2-receptor interactions, the main chain hydrogen bonds and the PPII conformation maximize both main chain and side chain interactions with the TRAF2 surface. 

It seems reasonable to attribute these facts to a conformational transition between two ordered structures, but at present we cannot specify the identity of these structures and cannot ascertain if this transition is correspondent to that of polyproline or not. 

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