Kinetics characterization of c-Src binding to lipid membranes: switching from labile to persistent binding

Abstract

Cell signaling by the c-Src proto-oncogen requires the attachment of the protein to the inner side of theplasma membrane through the myristoylated N-terminal region, known as the SH4 domain. Additionalbinding regions of lower affinity are located in the neighbor intrinsically disordered Unique domainand the structured SH3 domain. Here we present a surface plasmon resonance study of the binding of amyristoylated protein including the SH4, Unique and SH3 domains of c-Src to immobilized liposomes. Twodistinct binding processes were observed: a fast and a slow one. The second process lead to a persistentlybound form (PB) with a slower binding and a much slower dissociation rate than the first one. Theassociation and dissociation of the PB form could be detected using an anti-SH4 antibody. The kineticanalysis revealed that binding of the PB form follows a second order rate law suggesting that it involvesthe formation of c-Src dimers on the membrane surface. A kinetically equivalent PB form is observedin a myristoylated peptide containing only the SH4 domain but not in a construct including the threedomains but with a 12-carbon lauroyl substituent instead of the 14-carbon myristoyl group. The PB formis observed with neutral lipids but its population increases when the immobilized liposomes containnegatively charged lipids. We suggest that the PB form may represent the active signaling form of c-Srcwhile the labile form provides the capacity for fast 2D search of the target signaling site on the membranesurface