Lattice mobility and anomalous temperature factor behaviour in cytochrome c′

Atomic temperature factors (B-values) obtained from X-ray refinement experiments provide empirical estimates of protein mobility that have been correlated with both theoretical simulations of protein dynamics¹ and experimental studies of antibody reactivity^2,3. The comparison of B-values with protein solution properties requires adjustment of the apparent atomic mobilities to compensate for the effects of the crystal environment ^4-6. Here we compare crystallographically independent subunits of the dimeric cytochrome c′ from the bacterium Rhodospirillum molischianum to examine how lattice effects influence refined B-values. In addition to local effects on protein mobility at crystal contacts^4,5, we show that B-value differences up to 12 å² between subunits result from lattice disordering effects that approximate to concerted rotations of the molecules about a crystal symmetry axis.