Mechanical Signal Transduction via Phosphorylation of the Focal Adhesion Targeting Domain of Focal Adhesion Kinase

Abstract

Focal adhesion kinase (FAK) is a key component of the ECM-to-cytoskeleton signaling pathway triggered by mechanical stimulation. FAK's C-terminal focal adhesion targeting (FAT) domain, which binds to the LD motifs of the scaffold protein paxillin, localizes FAK to focal adhesions. Phosphorylation of FAT's Y925 promotes association between FAK and GRB2, activating the Erk2/MAPK pathway. Results of equilibrium and mechanically loaded MD simulations on FAT, bound at its two hydrophobic patches by LD motifs, are presented. Equilibrium simulations reveal that (i) FAT's N- and C-terminal tails shield Y925 from solvent exposure and (ii) FAT exhibits no proclivity for unfolding or loss of tertiary structure required for Y925 phosphorylation. Conversely, applied loads pull these tails away from Y925 and assist FAT's α-helix 1 unfolding. Thus, the degree of H1 unfolding provides a demonstration of a mechanism for Y925 phosphorylation under moderate loads over timescales ineffective in exposing Y925 in the absence of load. This provides a novel, atomically detailed illustration of mechanotransduction across a single protein-protein interaction--FAT/paxillin LD motif--at physiologically relevant load levels and time scales, all while mimicking mechanical constraints imposed by focal adhesions.View Large Image | View Hi-Res Image | Download PowerPoint Slide