ENERGETICS OF THE DISULFIDE BRIDGE - AN AB-INITIO STUDY

The energetics of the chi1(2)chi3chi(2)2 portion of the disulfide brid ge have been obtained from an ab initio study of diethyl disulfide. Ca lculations at the 3-21G level were done on relaxed structures at ever y approximately 30-degrees in chi(1)2 and chi2(2), and the additional energies for small DELTAchi3 were obtained. Complete E(chi1(2), chi2(2 )) and chi0(3)(chi1(2), chi2(2)) maps were computed from Fourier serie s expansions. These results have been used to calculate the energetics of 92 disulfide bridges in known protein structures, and to compare a b initio and molecular mechanics energies for some observed and predic ted bridges. The differences found in relative energies and in chi0(3) values suggest that present energy functions give a limited descripti on of the structural and energetic properties of the disulfide bridge. (C) 1993 John Wiley & Sons, Inc.