Determining the Molecular Composition of Synaptic Ribbons

Jason Chalifoux
Boston College

The objective of this study was to determine the molecular composition of synaptic ribbons. We developed a purification procedure for synaptic ribbons that facilitates the search for ribbon-related proteins. Results show that the purification is similar to the purification achieved by a previously published purification (Schmitz et al. 1996). In our search for an optimized lysis buffer, it was determined that chaotropic conditions used to solubilize unwanted proteins also solubilized the B16 antigen located on synaptic ribbons. This antigen was named SR118. SR118 is specific to the retina (not found in brain or liver) and can be immunoprecipitated by B16. SR118 injected into BALB/C mice induced antibodies to synaptic ribbons in tissue sections. Protein identification was accomplished with LC/MS/MS. Results showed that SR118 had considerable protein coverage to nucleolin and polypyrimidine tract binding protein-associated splicing factor (PTBSF). SR118 was treated with Ca2+. It was shown that Ca2+ effected the relative mobility of SR118. In summary, we have discovered SR118, a putative synaptic ribbon protein.