Residue-Dependent Transition Temperatures and Denaturant Midpoints in the Folding of a Multidomain Protein.

As a consequence of the finite size of globular proteins, it is expected that there should be dispersions in the global melting temperature (Tm) and the denaturation midpoint (Cm). Thermodynamic considerations dictate that the dispersions, ΔTm in Tm, and ΔCm in Cm, should decrease with N, the number of residues in the protein. We performed coarse-grained simulations of the self-organized polymer (SOP) model of the multidomain protein adenylate kinase (ADK) with N = 214 in order to calculate thermal and denaturation unfolding titration curves. The results show that ΔTm/Tm and ΔCm/Cm are nonzero and follow the previously established ( Phys. Rev. Lett. 2004, 93, 268107) thermodynamic 1/N scaling for proteins accurately. For ADK, the dispersions are small (≈0.004), which implies that the melting temperature is more or less unique, which is unlike in BBL (N = 40) where ΔTm/Tm ≈ 0.03.