PEPTIDE MODELS .16. THE IDENTIFICATION OF SELECTED HCO-L-SER-NH2 CONFORMERS VIA A SYSTEMATIC GRID SEARCH USING AB-INITIO POTENTIAL-ENERGY SURFACES

Multidimensional conformational analysis (MDCA) predicted the existenc e of nine stable backbone conformations (alpha(L), alpha(D), beta(L), gamma(L), gamma(D), delta(L), delta(D), epsilon(L), and epsilon(D)) on the 2D-Ramachandran map, E = E(phi, psi), for a single amino acid dia mide (HCONH-CHR-CONH2). The potential energy hypersurfaces (E = E[phi, psi, chi(1), chi(2)]) of For-L-Ser-NH2 associated with the alpha(L)-, beta(L)-, gamma(L)-, delta(L)-, and epsilon(L)-type stable backbone o rientations are investigated in this article. An appropriate number of side-chain rotamers is associated with each of the backbone conformer s. In the case of serine, where R = -CH2OH, the two sidechain torsiona l angles (chi(1), chi(2)) should lead to 33 = 9 different sidechain o rientations according to MDCA. For certain backbone structures, some o f the sidechain conformations were nonexistent. (C) 1996 by John Wiley & Sons, Inc.