The Molten Globule, and Two-State vs. Non-Two-State Folding of Globular Proteins

Abstract

From experimental studies of protein folding, it is now clear that there are two types of folding behavior, i.e., two-state folding and non-two-state folding, and understanding the relationships between these apparently different folding behaviors is essential for fully elucidating the molecular mechanisms of protein folding. This article describes how the presence of the two types of folding behavior has been confirmed experimentally, and discusses the relationships between the two-state and the non-two-state folding reactions, on the basis of available data on the correlations of the folding rate constant with various structure-based properties, which are determined primarily by the backbone topology of proteins. Finally, a two-stage hierarchical model is proposed as a general mechanism of protein folding. In this model, protein folding occurs in a hierarchical manner, reflecting the hierarchy of the native three-dimensional structure, as embodied in the case of non-two-state folding with an accumulation of the molten globule state as a folding intermediate. The two-state folding is thus merely a simplified version of the hierarchical folding caused either by an alteration in the rate-limiting step of folding or by destabilization of the intermediate.

Interdiction in the Early Folding of the p53 DNA-Binding Domain Leads to Its Amyloid-Like Misfolding

“…The final length of the topological elements of the 3D structure can vary from their open-chain seeding loops, as contacts in the folded structure are refined by optimal packing, secondary structure formation and the establishment of all the relevant interactions [ 49 ]. Because proteins longer than ~100 amino acids do not generally undergo a complete two-state collapse [ 44 , 50 ] but rather fold through multi-step pathways, consistent and simple physical reasoning implies that there is a limit to the size of the primary loop (i.e., ~100 amino acids) that can successfully lead to the native SCM folding pathway.…”

CD4+ T-Cell Epitope Prediction by Combined Analysis of Antigen Conformational Flexibility and Peptide-MHCII Binding Affinity

“… 71 Many proteins of fewer than 200 residues undergo two-state folding transitions. 72 Thus, small proteins yield little complexity in fragmentation by limited proteolysis, and the structures have little effect on antigen processing and epitope dominance. For the collection of model antigens, an average of 10% of the tested peptides contained epitopes.…”

“…The size minimum accounts for the fact that small proteins tend to have reduced conformational stability and lack complex domain structure . Many proteins of fewer than 200 residues undergo two-state folding transitions . Thus, small proteins yield little complexity in fragmentation by limited proteolysis, and the structures have little effect on antigen processing and epitope dominance.…”

DMSO-Quenched H/D-Exchange 2D NMR Spectroscopy and Its Applications in Protein Science

“…The H/D-exchange techniques have also been used effectively for studying non-native states, including equilibrium unfolding intermediates and transient intermediates in kinetic refolding reactions of proteins. The molten globule (MG) state, which has a substantial amount of secondary structure but lacks the specific tertiary side-chain packing characteristics of native proteins, is an equilibrium intermediate state under mildly denaturing conditions for numerous globular proteins, many with more than ~100 residues [22][23][24]. In the 1990s, the structural characterizations of the MG state by H/D-exchange 2D NMR were carried out for a number of globular proteins, including apomyoglobin [25], cytochrome c [26,27], α-lactalbumin [28][29][30][31][32], Ca 2+ -binding milk lysozyme [33,34], and other proteins [35][36][37][38][39][40][41].…”