Studying the structural properties of polyalanine and polyglutamine peptides.

Poly-(Ala) and poly-(Gln) peptides have important biological effects, and can cause various human illnesses and neurodegenerative diseases. Conformational analysis of these homo-oligopeptides (HOPs) was carried out by simulated annealing in order to identify their structural properties regarding secondary structures and intramolecular H-bonding patterns. Poly-(Ala) and poly-(Gln) peptides composed of 7, 10, 14 or 20 amino acids were modelled in both charged and terminally blocked forms. In the case of conformers derived from simulated annealing calculations, the presence of various secondary structural elements (different types of beta-turns, alpha-helix, 3(10)-helix, poly-proline II helix, parallel and antiparallel beta-strands) was investigated. Moreover, the intramolecular H-bonding patterns formed either between the backbone atoms for both HOPs or between the backbone and side-chain atoms for the poly-(Gln) peptides were examined. Our results showed that different secondary structural elements (type I and type III beta-turns, alpha-helix, 3(10)-helix, antiparallel beta-strand) could be observed in both poly-(Ala) and poly-(Gln) peptides and, according to their presence, characteristic H-bonding patterns formed mainly by i<--i+3 and i<--i+4 H-bonds could be found.