Synaptotagmin V: a novel synaptotagmin isoform expressed in rat brain.

Regulated Ca(2+)-dependent release of transmitters from synaptic vesicles is an important characteristic of chemical neurotransmission. Synaptotagmins are abundant synaptic vesicle transmembrane proteins that probably function as Ca2+ sensors. Molecular cloning has identified four different synaptotagmin isoforms in mammals. We report here the cloning and sequencing of a novel isoform of 386 amino acids. Synaptotagmin V is 54% identical in sequence to synaptotagmin I and possesses all the domains that characterise this multigene family. It is expressed at high levels in rat brain, but not in spinal cord or a number of peripheral non-neuronal tissues.