CONFORMATIONAL-ANALYSIS BY MOLECULAR MECHANICS ENERGY MINIMIZATIONS OF THE TETRAPEPTIDE BOC-GLY-LEU-GLY-GLY-NME, A RECURRING SEQUENCE OF ELASTIN

The amino acid sequences Gly-X-Gly-Gly (X = Ala, Val, Leu, Ile) frequently recur in elastin and might play a role in the molecular mechanism of protein elasticity. In this paper we report on a theoretical conformational analysis by molecular mechanics energy minimizations of the tetrapeptide Boc-Gly-Leu-Gly-Gly-NMe, using a strategy based on the build-up method for searching exhaustively the conformational space. The set of 3785 conformers has been determined and a statistical analysis has been carried out. The conformers' energy, end-to-end distance, torsions and >C=O ... HN< interaction distance distributions are discussed. The stability of type II beta-turn Gly-1-C=O ... HNGly-4, within the conformer family (experimentally observed), and C-7 HNLeu-2, C-7 HNMe and C-10 HNMe hydrogen bonds (hypothesized according to experimental results), have been theoretically verified. The possible role of librational motions and sliding beta-turns for the entropic elasticity mechanism of elastin is discussed.