Synapsin I interacts with c-Src and stimulates its tyrosine kinase activity.
Synapsin I is a synaptic vesicle-associated phosphoprotein that has been implicated in the formation of presynaptic specializations and in the regulation of neurotransmitter release. The nonreceptor tyrosine kinase c-Src is enriched on synaptic vesicles, where it accounts for most of the vesicle-associated tyrosine kinase activity. Using overlay, affinity chromatography, and coprecipitation assays, we have now shown that synapsin I is the major binding protein for the Src homology 3 (SH3) domain of c-Src in highly purified synaptic vesicle preparations. The interaction was mediated by the proline-rich domain D of synapsin I and was not significantly affected by stoichiometric phosphorylation of synapsin I at any of the known regulatory sites. The interaction of purified c-Src and synapsin I resulted in a severalfold stimulation of tyrosine kinase activity and was antagonized by the purified c-Src-SH3 domain. Depletion of synapsin I from purified synaptic vesicles resulted in a decrease of endogenous tyrosine kinase activity. Portions of the total cellular pools of synapsin I and Src were coprecipitated from detergent extracts of rat brain synaptosomal fractions using antibodies to either protein species. The interaction between synapsin I and c-Src, as well as the synapsin I-induced stimulation of tyrosine kinase activity, may be physiologically important in signal transduction and in the modulation of the function of axon terminals, both during synaptogenesis and at mature synapses.
Onofri
F
F
Department of Experimental Medicine and Biochemical Sciences, University of Roma Tor Vergata, Via di Tor Vergata 135, 00133 Rome, Italy.
Giovedì
S
S
Vaccaro
P
P
Czernik
A J
AJ
Valtorta
F
F
De Camilli
P
P
Greengard
P
P
Benfenati
F
F
D000818:Animals; D001665:Binding Sites; D004789:Enzyme Activation; D010446:Peptide Fragments / Q000378:metabolism; D011233:Precipitin Tests; D016548:Prosencephalon; D011485:Protein Binding; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D051381:Rats; D013347:Subcellular Fractions; D016704:Synapsins / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism*; D018909:src Homology Domains
D010446:Peptide Fragments; D016704:Synapsins; D016392:Proto-Oncogene Proteins pp60(c-src)