Binding-induced folding under unfolding conditions: Switching between induced fit and conformational selection mechanisms

Sreemantee Sen,Jayant B Udgaonkar

doi:10.1074/jbc.ra119.009742

Abstract

The chemistry of protein-ligand binding is the basis of virtually every biological process. Ligand binding can be essential for a protein to function in the cell by stabilizing or altering the conformation of a protein, particularly for partially or completely unstructured proteins. However, the mechanisms by which ligand binding impacts disordered proteins or influences the role of disorder in protein folding is not clear. To gain insight into this question, the mechanism of folding induced by the binding of a Pro-rich peptide ligand to the SH3 domain of phosphatidylinositol 3-kinase unfolded in the presence of urea has been studied using kinetic methods. Under strongly denaturing conditions, folding was found to follow a conformational selection (CS) mechanism. However, under mildly denaturing conditions, a ligand concentration-dependent switch in the mechanism was observed. The folding mechanism switched from being predominantly a CS mechanism at low ligand concentrations to being predominantly an induced fit (IF) mechanism at high ligand concentrations. The switch in the mechanism manifests itself as an increase in the reaction flux along the IF pathway at high ligand concentrations. The results indicate that, in the case of intrinsically disordered proteins too, the folding mechanism is determined by the concentration of the ligand that induces structure formation.

Highlights

The chemistry of protein–ligand binding is the basis of virtually every biological process
The results indicate that, in the case of intrinsically disordered proteins too, the folding mechanism is determined by the concentration of the ligand that induces structure formation
Because folding is induced by ligand binding (Fig. 1), at equilibrium, both the ligand-bound N state and the ligand-bound U state will contribute to the fraction of protein with bound ligand

Summary

Introduction

The chemistry of protein–ligand binding is the basis of virtually every biological process. The sequential model [3] posited a conformational change upon ligand binding, whereas the concerted model [4] posited the pre-existence of at least two conformational states to which ligand could bind These models were proposed to explain the allostery seen in the case of many multimeric proteins, the same concepts of. It becomes possible to study the folding reaction at high denaturant concentration [5, 6]. This capability enables an important question in protein folding to be addressed: is the mechanism of folding at high denaturant concentration the same as that at low denaturant concentration?

Methods

Results

Discussion

Conclusion