Roles for Synapsins in Regulation of Synaptic Vesicle Traffic.

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Homo- and heterodimerization of synapsins.Synapsins contain a central ATP-binding domain, the C-domain, that is highly homologous between synapsins and evolutionarily conserved in invertebrates. The crystal structure of the C-domain from synapsin I revealed that it constitutes a large (>300 amino acids), independently folded domain that forms a tight dimer with or without bound ATP.I have shown that the C-domains of all synapsins form homodimers, and that in addition, C-domains from different synapsins associate into heterodimers.A phospho-switch controls the dynamic association of synapsins with synaptic vesicles.Synapsins constitute a family of synaptic vesicle proteins essential for regulating neurotransmitter release. Only two domains are conserved in all synapsins : a short N-terminal A dontain with a single phosphorylation site for cAMP-dependent protein kinase (PKA) and CaM Kinase I, and a large central C domain that binds ATP and may be enzymatic. I have demonstrated that synap … More sin phosphorylation in the A domain, at the only phosphorylation site shared by all synapsins, dissociates synapsins from synaptic vesicles. Furthermore, we show that the A domain binds phospholipids and is inhibited by phosphorylation.Cyclosporine A-induced hypertension involves synapsin in renal sensory nerve endings.Synapsins are a family of synaptic vesicle phosphoproteins that are essential for normal regulation of neurotransmitter release at synapses. In addition to synaptic vesicles, synapsins are found on microvesicles in sensory nerve endings in peripheral tissues. However, the functions of the sensory microvesicles in general, and of synapsins in particular, are unknown. I have demonstrated in a mouse model that cyclosporine A (CsA) raises blood pressure by stimulating renal sensory nerve endings that contain synapsin-positive microvesicles. In knockout mice lacking synapsin I and II, sensory nerve endings are normally developed but not stimulated by CsA.The reflex activation of efferent sympathetic nerve activity and the increase in blood pressure by CsA seen in control are greatly attenuated in synapsin-deficient mice. These results provide a mechanistic explanation for CsA-induced acute hypertension and suggest that synapsins could serve as a drug target in this refractory condition. Furthermore, these data establish evidence that synapsin-containing sensory microvesicles perform an essential role in sensory transduction and suggest a role for synapsin phosphorylation in th is process. Less