Effect of genetic variation on the thermal stability of human serum albumin

Reversible thermal denaturation of 33 genetic variants of human serum albumin (HSA) appeared to be a two-state process when studied by circular dichroism (CD). Fourteen single-residue variants have Tm values (midpoint of denaturation) higher than, and nine have Tm values lower than, their endogenous, wild-type counterpart. Nine single-residue variants have ΔHv values (van't Hoff enthalpy) higher than, and 14 have ΔHv values lower than, normal albumin. All types of combinations of positive and negative ΔTm values and Δ(ΔHv) values were found. Good linear correlations between mutation-induced changes of α-helical content and Δ(ΔHv) values, but not ΔTm values, were found especially for the variants mutated in domains I and III. The effect of altered chain length and glycosylation on Tm and ΔHv was also studied. For all variants, no clear relationship was found between the changes in the thermodynamic parameters and the type of substitution, changes in protein charge or hydrophobicity. However, the protein changes taking place in domain I have a rather uniform effect (almost all of the nine variants have positive ΔTm values and negative Δ(ΔHv) values, i.e., they denature more easily than normal albumin but they do so at a higher temperature). The present results can be of both protein chemical relevance and of clinical interest, because they could be useful when designing stable, recombinant HSAs for clinical applications.