Single-Molecule Study of Protein−Protein Interaction Dynamics in a Cell Signaling System

Abstract

We report a study on protein−protein noncovalent interactions in an intracellular signaling protein complex, using single-molecule spectroscopy and molecular dynamics (MD) simulations. A Wiskott−Aldrich Syndrome Protein (WASP) fragment that binds only the activated intracellular signaling protein Cdc42 was labeled with a novel solvatochromic dye and used to probe hydrophobic interactions significant to Cdc42/WASP recognition. The study shows static and dynamic inhomogeneous conformational fluctuations of the protein complex that involve bound and loosely bound states. A two-coupled, two-state Markovian kinetic model is proposed for the conformational dynamics. The MD simulations explore the origin of these conformational states and associated conformational fluctuations in this protein−protein interaction system.