Analysis of the stability of multimeric proteins by effective Δ G and effective m ‐values

Abstract Analyzing the stability of a multimeric protein is challenging because of the intrinsic difficulty in handling the mathematical model for the folded multimer‐unfolded monomer equilibrium. To circumvent this problem, we introduce the concept of effective stability, Δ G eff (= − RT ln K eff ), where K eff is the equilibrium constant expressed in monomer units. Analysis of the denaturant effect on Δ G eff gives new insight into the stability of multimeric proteins. When a multimeric protein is mostly folded, the dependence of effective stability on denaturant concentration (effective m ‐value) is simply the m ‐value of its monomeric unit. However, when the protein is mostly unfolded, its stability depends on denaturant concentration with the m ‐value of its multimeric form. We also find that the effective m ‐value at the C m is a good approximation of the apparent m ‐value determined by fitting the equilibrium unfolding data from multimeric proteins with a two‐state monomer model. Moreover, when the m‐ value of a monomeric unit is estimated from its size, the effective stability of a multimeric protein can be determined simply from C m and this estimated m ‐value. These simple and intuitive approaches will allow a facile analysis of the stability of multimeric proteins. These analyses are also applicable for high‐throughput analysis of protein stability on a proteomic scale.