Ab initio protein phasing:: the Patterson deconvolution method in SIR2002

An automated Patterson deconvolution technique, based on the minimum superposition function, has been implemented into the SIR2002 package, a program for the ab initio determination of small and large molecules. The procedure, combined with the direct-space phase refinement routines present in the SIR2002 program, has been designed to solve proteins diffracting at atomic resolution. The procedure has been validated using a large set of test structures, containing either heavy or intermediate atoms ( e. g. P, S and Cl) and with structural complexity up to 1500 non-hydrogen atoms in the asymmetric unit. The success, obtained in a completely automatic way, requires a very short computing time and indicates that Patterson deconvolution techniques are a valid alternative to current direct-methods approaches.