Role of medium- and long-range interactions to the stability of the mutants of T4 lysozyme.

Inter-residue interactions play an important role to the folding and stability of protein molecules. In this work, we analyze the role of medium- and long-range interactions to the stability of T4 lysozyme mutants. We found that, in buried mutations, the increase in long-range contacts upon mutations destabilizes the protein, whereas, in surface mutations, the increase in long-range contacts increases the stability, indicating the importance of surrounding polar residues to the stability of surface mutations. Further, the increase in medium-range contacts decreases the stability of buried and surface mutations and a direct relationship is observed between the increase of medium-range contacts and increase in stability for partially buried/exposed mutations. Moreover, the relationship between amino acid properties and stability of T4 lysozyme mutants at positions Ile3, Phe53, and Leu99 showed that the effect of medium- and long-range contacts is less for buried mutations and the inter-residue contacts have significant correlation with the stability of partially buried mutations.