Glassy dynamics of side-chain ordering in a simple model of protein folding.

We introduce a modified version of protein lattice models in which monomers have several spin states, representing side-chain rotamers. Completion of folding corresponds to reaching the native backbone configuration with complete ordering of side chains. We find that as temperature is lowered, side-chain ordering becomes much slower than backbone folding. The presence of side chains leads to nonexponential kinetics and a broad distribution of relaxation times.