Energetics of Side Chain Packing in Staphylococcal Nuclease Assessed by Exchange of Valines, Isoleucines, and Leucines

Citations Over Time

Abstract

To examine the importance of side chain packing to protein stability, each of the 11 leucines in staphylococcal nuclease was substituted with isoleucine and valine. The nine valines were substituted with leucine and isoleucine, while the five isoleucines, previously substituted with valine, were substituted with leucine and methionine. These substitutions conserve the hydrophobic character of these side chains but alter side chain geometry and, in some cases, size. In addition, eight threonine residues, previously substituted with valine, were substituted with isoleucine to test the importance of packing at sites normally not occupied by a hydrophobic residue. The stabilities of these 58 mutant proteins were measured by guanidine hydrochloride denaturation. To the best of our knowledge, this is the largest library of single packing mutants yet characterized. As expected, repacking stability effects are tied to the degree of side chain burial. The average energetic cost of moving a single buried methyl group was 0.9 kcal/mol, albeit with a standard deviation of 0.8 kcal/mol. This average is actually slightly greater than the value of 0.7-0.8 kcal/mol estimated for the hydrophobic transfer energy of a methylene from octanol to water. These results appear to indicate that van der Waals interactions gained from optimal packing are at least as important in stabilizing the native state of proteins as hydrophobic transfer effects.

Related Papers

• → Amino acid interactions in chick nutrition(1970)111 cited
• → Isoleucine requirement of broiler chicks as affected by the concentrations of leucine and valine in practical diets(1992)27 cited
• → Leucine, Isoleucine and Valine Interactions in Turkey Poults(1976)38 cited
• → Amino acid requirements of the young turkey: Leucine, isoleucine and valine(1975)30 cited
• → Plasma concentrations and dietary requirements of leucine, isoleucine and valine: Studies with the young chick(1974)22 cited