Protein stability effects of a complete set of alanine substitutions in Arc repressor

The equilibrium stabilities of a complete set of single alanine-substitution mutants of the Arc repressor of bacteriophage P22 have been determined by thermal and urea denaturation experiments. Only half the alanine substitutions cause significant changes in stability, with the most deleterious mutations affecting side chains in the hydrophobic core or in salt bridges and hydrogen bonds which are protected from solvent. The five mutations that are most destabilizing affect a cluster of core residues that seem to form a structural foundation for Arc.