Synaptophysin is the major integral membrane protein of small synaptic vesicles. It belongs to a family of proteins which includes synaptogyrin and synaptoporin. The protein contains 4 transmembrane domains and cytoplasmic N- and C-termini. There are two intravesicular loops that contain disulfide bonds. The protein is N-glycosylated on the first intravesicular loop, a modification important for the synaptic vesicle targeting of synaptophysin. Indeed, a mutant form of the protein, unable to undergo glycolysation, leads to the accumulation of the protein in the cell body of neurons indicating that N-glycosylation is required for the synaptic localization of synaptophysin5. The C-terminal tail is extensively phosphorylated on Tyr residues. However, the biological significance of the post-translational modification is not yet determined
