WHO CHECKS THE CHECKERS - 4 VALIDATION TOOLS APPLIED TO 8 ATOMIC-RESOLUTION STRUCTURES

Eight protein crystal structures, which have been refined against X-ra y diffraction data extending to atomic resolution, 1.2 Angstrom or bet ter, were inspected using four different validation tools, PROCHECK, P ROVE, SQUID and WHATCHECK. Two general questions were addressed. (1) D o the structures imply changes in ''expected'' stereochemical properti es and are the target values used for restraints in the validation pro grams and the refinement protocol appropriate? (2) Can errors in model s be detected acid how reliable are the coordinates after refinement? Preliminary analysis by members of the network led to modifications bo th to the validation programs and to the refinement protocols. The res ults of the final analyses are reported here. Apparent discrepancies i n cell dimensions were identified. Most stereochemical properties are shown to be more tightly clustered than for lower resolution analyses. In contrast the omega angle has a wider distribution. The validation software is generally available and can be accessed at servers listed at the end of the paper. (C) 1998 Academic Press Limited.