Effect of hydrophobic core packing on sidechain dynamics

The effect of hydrophobic core packing on sidechain dynamics was analyzed b y 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 ov erall level of dynamics is only subtly different from WT. However, the muta tions caused a redistribution in the positions of core residues that are dy namic. This correlates with the tendency of these residues to populate unfa vorable rotamers, suggesting that strain from poor sidechain conformations may promote increased flexibility as a mechanism to relieve unfavorable ste ric interactions. The results demonstrate that even when core volume is con served, different packing arrangements in mutants can alter dynamic behavio r.