Heat capacity of folding of proteins corrected for disulfide cross-links

Abstract

The heat capacities (Δ C p,f) for the temperature-induced folding of proteins: barnase, lysozyme T4, papain, trypsin, ribonuclease T1, chymotrypsin, lysozyme and ribonuclease A have been calculated from the change in solvent accessible surface area between the native state and extended polypeptide chain. To visualize the effect of disulfide cross-links on molar heat capacity, loops of varying number of alanine residues and extended alanine chains with terminal cystein are modeled. The difference in Δ C p values between the extended state and the loop conformation of proteins is linearly related to the number of residues in the loop. Corrections to the heat capacity of folding (Δ C p,f) are applied for proteins with cross-links based on this observation. There is good correlation between corrected values of Δ C p,f and experimental values.