Polar group burial contributes more to protein stability than nonpolar group burial.

On the basis of studies of Asn to Ala mutants, the gain in stability from burying amide groups that are hydrogen bonded to peptide groups is 80 cal/(mol A(3)). On the basis of similar studies of Leu to Ala and Ile to Val mutants, the gain in stability from burying -CH(2)- groups is 50 cal/(mol A(3)). Thus, the burial of an amide group contributes more to protein stability than the burial of an equivalent volume of -CH(2)- groups. Applying these results to folded proteins leads to the surprising conclusion that peptide group burial makes a larger contribution to protein stability than nonpolar side chain burial. Several studies have shown that the desolvation penalty for burying peptide groups is considerably smaller than generally thought. This suggests that the hydrogen bonding and van der Waals interactions of peptide groups in the tightly packed interior of folded protein are more favorable than similar interactions with water in the unfolded protein.