ON BUILDING A DATA-BANK OF TRANSFERABLE EXPERIMENTAL ELECTRON-DENSITYPARAMETERS - APPLICATION TO POLYPEPTIDES

A comparison between electron density multipole parameters from severa l high-resolution X-ray diffraction analyses of peptides is presented. The parameters of the same type of atoms in the same chemical environ ment are statistically equal. Therefore, these average parameters were used as fixed parameters in a conventional X-ray refinement of two lo w-order data sets of pGlu-Phe-D-Pro-phi[CN4]-Me (T = 125 K, sin theta/ lambda < 0.65 Angstrom(-1); room temperature, sin theta/lambda < 0.76 Angstrom(-1)). After this refinement, the thermal displacement paramet ers are physically meaningful, and difference Fourier maps reveal the deformation density of the molecule. Further application of this trans ferability is molecular modeling and calculation of electrostatic pote ntial of big peptides or proteins as soon as an experimental electron density data bank is available.