Tyrosine phosphorylation of synaptophysin in synaptic vesicle recycling

Abstract

The integral SV (synaptic vesicle) protein synaptophysin was one of the first nerve terminal proteins identified. However its role, if any, in the SV life cycle remains undetermined. One of the most prominent features of synaptophysin is that its cytoplasmic C-terminus largely consists of pentapeptide repeats initiated by a tyrosine residue. Synaptophysin is heavily phosphorylated by tyrosine kinases in the nerve terminal, suggesting that this phosphorylation is central to its function. This review will cover the evidence for tyrosine phosphorylation of synaptophysin and how this phosphorylation may control its function in the SV life cycle.

Figure 1

Alignment of the amino acid sequence of the C-termini of synaptophysin (Syp I), synaptophysin II (Syp II) and synaptogyrin (Syg I). Synaptophysin has nine putative tyrosine residues for phosphorylation whereas synaptophysin II contains only five and is not tyrosine phosphorylated (unpublished observations [11]). Synaptogyrin has six possible sites and is tyrosine phosphorylated. Black bars indicate shared amino acid homology between at least 2 protein sequences.