A Maximum Caliber analysis of the Foldon Hypothesis

Abstract

Different models of protein folding favor different mechanisms. Some models rely on a defined pathway, while other models rely on a more heterogeneous set of pathways. The Foldon Hypothesis is based on the concept of a defined pathway. According to the Foldon Hypothesis, protein folding is characterized by the stepwise assembly of small, cooperative units called foldons. The Maximum Caliber (Max Cal) method provides an opportunity to test this model. The Max Cal method gives the probabilities for dynamical trajectories, in much the same way that the maximum entropy principle gives the probabilities for equilibrium states. In this study, the Max Cal method was applied to folding data for the protein cytochrome c (cyt c; Hu W, Kan ZY, Mayne L, Englander SW. Proc Natl Acad Sci U S A. 2016;113:3809-3814). The overall picture to emerge from this analysis is that the data do not require a dominant, defined pathway. The folding of cytochrome c is likely a heterogeneous process that includes multiple pathways.