Figure 18.2.2.1 

Effect of resolution on coordinate-error estimates: accuracy as a function of resolution. Refinements were begun with the crystal structure of penicillopepsin (Hsu et al., 1977) with water molecules omitted and with uniform temperature factors. The low-resolution limit was set to 6 Å. Inclusion of all low-resolution diffraction data does not change the conclusions (Adams et al., 1997). The penicillopepsin diffraction data were artificially truncated to the specified high-resolution limit. Each refinement consisted of simulated annealing using a Cartesian-space slow-cooling protocol starting at 2000 K, overall B-factor refinement and individual restrained B-factor refinement. All refinements were carried out with 10% of the diffraction data randomly omitted for cross validation. (a) Coordinate-error estimates of the refined structures using the methods of Luzzati (1952) and Read (1986). All observed diffraction data were used, i.e. no cross validation was performed. The actual coordinate errors (r.m.s. differences to the original crystal structure) are shown for comparison. (b) Cross-validated coordinate-error estimates. The test set was used to compute the coordinate-error estimates (Kleywegt & Brünger, 1996).