SYNAPSIN IIA BUNDLES ACTIN-FILAMENTS

Synapsins are neuron-specific phosphoproteins associated with small sy naptic vesicles in the presynaptic nerve terminal. Synapsin I, which h as been demonstrated to bundle F-actin in vitro, has been postulated t o regulate neurotransmitter release by cross-linking synaptic vesicles to the actin cytoskeleton. To investigate the possible interaction of synapsin II with actin filaments, we expressed synapsin II in Spodopt era frugiperda and High Five insect cells using a recombinant baculovi rus. Purified recombinant synapsin IIa was incubated with F-actin, and bundle formation was evaluated by light scattering and electron micro scopy. Synapsin IIa was found to bundle actin filaments. Dose-response curves indicated that synapsin IIa was more potent than synapsin I in bundling actin filaments. These data suggest that synapsin IIa may cr oss-link synaptic vesicles and actin filaments in the nerve terminal.