Effect of hydrophobic core packing on sidechain dynamics.

The effect of hydrophobic core packing on sidechain dynamics was analyzed by comparing the dynamics of wild-type (WT) ubiquitin to those of a variant which has seven core mutations. This variant, 1D7, was designed to resemble WT by having a well-packed core of similar volume, and we find that its overall level of dynamics is only subtly different from WT. However, the mutations caused a redistribution in the positions of core residues that are dynamic. This correlates with the tendency of these residues to populate unfavorable rotamers, suggesting that strain from poor sidechain conformations may promote increased flexibility as a mechanism to relieve unfavorable steric interactions. The results demonstrate that even when core volume is conserved, different packing arrangements in mutants can alter dynamic behavior.