ISOFORM-SPECIFIC INTERACTION OF THE ALPHA(1A) SUBUNITS OF BRAIN CA2-25( CHANNELS WITH THE PRESYNAPTIC PROTEINS SYNTAXIN AND SNAP)

Presynaptic Ca2+ channels are crucial elements in neuronal excitation- secretion coupling. In addition to mediating Ca2+ entry to initiate tr ansmitter release, they are thought to interact directly with proteins of the synaptic vesicle docking/fusion machinery. Here we report isof orms-specific, stoichiometric interaction of the BI and rbA isoforms o f the alpha(1A) subunit of P/Q-type Ca2+ channels with the presynaptic membrane proteins syntaxin and SNAP-25 in vitro and in rat brain memb ranes. The BI isoform binds to both proteins, while only interaction w ith SNAP-25 can be detected in vitro for the rbA isoform. The synaptic protein interaction (''synprint'') site involves two adjacent segment s of the intracellular loop connecting domains II and III between amin o acid residues 722 and 1036 of the BI sequence. This interaction is c ompetitively blocked by the corresponding region of the N-type Ca2+ ch annel, indicating that these two channels bind to overlapping regions of syntaxin and SNAP-25. Our results provide a molecular basis for a p hysical link between Ca2+ influx into nerve terminals and subsequent e xocytosis of neurotransmitters at synapses that have presynaptic Ca2channels containing alpha(1A) subunits.