Oligomerization characteristics of cysteine string protein.

CSP function is vital to synaptic transmission, however; the precise nature of its role remains controversial. Conflicting reports support either a role for CSP: (i) in exocytosis or (ii) in the regulation of transmembrane calcium fluxes. Here we have examined the self-association of CSP to form oligomers that are stable upon SDS-PAGE. To understand the structural requirements for CSP self-association a series of CSP deletion mutants were constructed, expressed, and purified. This analysis revealed an interesting pattern of oligomerization. Amino acids between 83 and 136 were observed to be important for self-association. The recombinant CSP oligomers as well as the CSP monomers directly associate with Ni(2+)-NTA agarose. Thus CSP-CSP interactions may be an important consideration for current working models of CSP chaperone activity at the synapse.