Alleviation of a defect in protein folding by increasing the rate of subunit assembly

Understanding the nature of protein grammar is critical because amino acid substitutions in some proteins cause misfolding and aggregation of the mutant protein resulting in a disease state. Amino acid substitutions in phage P22 coat protein, known as tsf (temperature-sensitive folding) mutations, cause folding defects that result in aggregation at high temperatures. We have isolated global su (suppressor) amino acid substitutions that alleviate the tsf phenotype in coat protein (Aramli, L. A., and Teschke, C. M. (1999) J. Biol. Chem. 274, 22217-22224). Unexpectedly, we found that a global su amino acid substitution in tsf coat proteins made aggregation worse and that the tsf phenotype was suppressed by increasing the rate of subunit assembly, thereby decreasing the concentration of aggregation-prone folding intermediates.