What is "tomosyn"

In biology, tomosyn is a protein with approximately 1,100 amino acids. Two functional domains were originally identified, including one which binds to syntaxin, but recent crystallization of the yeast homolog Sro7 revealed that tomosyn likely has three functional domains: one WD40 domain and one syntaxin-binding domain, as previously recognized, but also another WD40 domain. The study also suggested that tomosyn's 'syntaxin binding domain' is not the reason tomosyn is inhibitory for neurotransmitter release, as originally proposed. Positional cloning suggested that tomosyn might inhibit neurotransmitter secretion in Caenorhabditis elegans neurons. This hypothesis was tested and confirmed , showing that tomosyn specifically inhibits synaptic vesicle priming—the biochemical step immediately preceding vesicle fusion and neurotransmitter release.