PEPTIDE MODELS XXI. Side-chain/backbone conformational interconversions inHCO-L-Ser-NH2. Tracing relaxation paths by ab initio modeling. An exploratory study

Conformational motion of HCO-L-Ser-NH2 takes place on the four-dimensional space of f(phi, psi, chi(1), chi(2)). For all backbone conformation types ( such as the building unit of an alpha-helix, beta-pleated sheet, inverse ga mma-turn, etc.), selected two-dimensional cross-sections (lambda(alpha L)(r elax) [chi(1), chi(2)], f(beta L)(relax) [chi(1), chi(2)], f(gamma L)(relax ) [chi(1), chi(2)] etc.) of the above four-dimensional hyperspace were calc ulated as the HF/3-21G level of theory. The analysis of the above ab initio conformation energy maps made the tracing of some relaxation paths possibl e which led to the monitoring of the side-chain-induced backbone conformati onal shifts operative in HCO-L-Ser-NH2. For most peptide models the present surface analysis makes it possible to monitor the side-chain-induced backb one modification via relaxation paths. (C) 1998 Elsevier Science B.V. All r ights reserved.