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

Abstract

The heat capacities (ΔC_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 ΔC_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 (ΔC_p,f) are applied for proteins with cross-links based on this observation. There is good correlation between corrected values of ΔC_p,f and experimental values.