REVERSE HYDROPHOBIC EFFECTS RELIEVED BY AMINO-ACID SUBSTITUTIONS AT A PROTEIN SURFACE

IT is rare for amino-acid substitutions on the surface of proteins to have large stabilizing or destabilizing effects1. Nevertheless, one substitution of this type, the Tyr 26 → Cys mutation in λ Cro, increases the melting temperature of the protein by 11°C and the stability by 2.2 kcal mol-1 (ref. 2). Here we show that the stability of Cro can be increased by many different amino-acid substitutions at position 26, with increasing stability showing a good correlation with decreasing side-chain hydrophobicity. As Tyr 26 is hyper-exposed to solvent in the Cro crystal structure3,4, we suggest that wild-type and variant proteins with other hydrophobic side chains at position 26 are destabilized as a result of a reverse hydrophobic effect caused by the side chain being more exposed to solvent in the native than in the denatured state. © 1990 Nature Publishing Group.