Multidisciplinary studies have led to the discovery and characterizati
on of cysteine string proteins (csps) in both Drosophila and Torpedo.
Phenotypic analysis of csp mutants in Drosophila demonstrates a crucia
l role for csp in synaptic transmission. Expression studies of Torpedo
csp (Tcsp) in Xenopus oocytes suggests that the protein has some role
in the function of presynaptic Ca2+ channels. However, biochemical pu
rification of Tcsp indicates that is associated with synaptic vesicles
rather than with the plasma membrane of presynaptic terminals where C
a2+ channels reside. These results suggest a model in which csps serve
as a link by which docked synaptic vesicles could modulate the activi
ty of presynaptic Ca2+ channels.