Abstract
Abstract Synaptotagmin I (Syt I) is a synaptic vesicle membrane protein that contains two copies of highly conserved protein kinase C homology regions known as the C2A and C2B domains. The C2A domain binds Ca2+ and the C2B domain binds inositol high polyphosphates (IP4, IP5, and IP6). It has been reported that Ca2+ regulated exocytosis of secretory vesicles is proposed to be activated by Ca2+ binding to the C2A domain and inhibited by inositol polyphosphate binding to the C2B domain. Syt I is also known to be present in neuronal growth cone vesicles. Affinity elution chromatography from the C2 domain of Syt I-immobilized Sepharose using IP6 as the eluent found that several proteins, including an adaptin, specific subunits of the clathrin assembly protein, AP-2 were eluted from the mouse brain. It suggests that inositol high polyphosphate-binding to the C2B domain of Syt I alter the state of protein–protein interaction including the Syt I–AP-2 interaction. Thus, the inositol high polyphosphate may result in the inhibition of events involved in the synaptic vesicle trafficking. In this study, we used NMR to solve the C2B-IP6 3D complex structure. Our data provide new evidence for the hypothesis that the conformational change of C2B binding to IP6 alter the interface of C2B- AP-2. This information will aid in the design of better pharmacological treatments for neurological disorders.