Specificity of the binding of synapsin I to Src homology 3 domains.
Synapsins are synaptic vesicle-associated phosphoproteins involved in synapse formation and regulation of neurotransmitter release. Recently, synapsin I has been found to bind the Src homology 3 (SH3) domains of Grb2 and c-Src. In this work we have analyzed the interactions between synapsins and an array of SH3 domains belonging to proteins involved in signal transduction, cytoskeleton assembly, or endocytosis. The binding of synapsin I was specific for a subset of SH3 domains. The highest binding was observed with SH3 domains of c-Src, phospholipase C-gamma, p85 subunit of phosphatidylinositol 3-kinase, full-length and NH(2)-terminal Grb2, whereas binding was moderate with the SH3 domains of amphiphysins I/II, Crk, alpha-spectrin, and NADPH oxidase factor p47(phox) and negligible with the SH3 domains of p21(ras) GTPase-activating protein and COOH-terminal Grb2. Distinct sites in the proline-rich COOH-terminal region of synapsin I were found to be involved in binding to the various SH3 domains. Synapsin II also interacted with SH3 domains with a partly distinct binding pattern. Phosphorylation of synapsin I in the COOH-terminal region by Ca(2+)/calmodulin-dependent protein kinase II or mitogen-activated protein kinase modulated the binding to the SH3 domains of amphiphysins I/II, Crk, and alpha-spectrin without affecting the high affinity interactions. The SH3-mediated interaction of synapsin I with amphiphysins affected the ability of synapsin I to interact with actin and synaptic vesicles, and pools of synapsin I and amphiphysin I were shown to associate in isolated nerve terminals. The ability to bind multiple SH3 domains further implicates the synapsins in signal transduction and protein-protein interactions at the nerve terminal level.
Onofri
F
F
Department of Experimental Medicine, Section of Physiology, University of Genova, Via Benedetto XV 3, I-16132 Genova, Italy.
Giovedi
S
S
Kao
H T
HT
Valtorta
F
F
Bongiorno Borbone
L
L
De Camilli
P
P
Greengard
P
P
Benfenati
F
F
D000818:Animals; D002417:Cattle; D011485:Protein Binding; D011817:Rabbits; D015398:Signal Transduction; D013379:Substrate Specificity; D016704:Synapsins / Q000737:chemistry* / Q000378:metabolism; D018909:src Homology Domains
D016704:Synapsins