The domain of brain beta-spectrin responsible for synaptic vesicle association is essential for synaptic transmission

We have examined the interaction between synapsin I, the major phosphoprote in on the membrane of small synaptic vesicles, and brain spectrin. Using re combinant peptides we have localized the synapsin I attachment site upon th e beta -spectrin isoform beta SpII SigmaI to a region of 25 amino acids, re sidues 211 through 235. This segment is adjacent to the actin binding domai n and is within the region of the beta SpII SigmaI that we previously predi cted as a candidate synapsin I binding domain based upon sequence homology. We used differential centrifugation techniques to quantitatively assess th e interaction of spectrin with synaptic vesicles. Using this assay, high af finity saturable binding of recombinant beta SpII SigmaI proteins was obser ved with synaptic vesicles. Binding was only observed when the 25 amino aci d synapsin I binding site was included on the recombinant peptides. Further , we demonstrate that antibodies directed against 15 amino acids of the syn apsin I binding domain specifically blocked synaptic transmission in cultur ed hippocampal neurons. Thus, the synapsin 1 attachment site on beta SpII S igmaI spectrin comprises a similar to 25 amino acid segment of the molecule and interaction of these two proteins is an essential step for the process of neurotransmission. (C) 2000 Elsevier Science B.V. All rights reserved.