Three splicing variants of tomosyn and identification of their syntaxin-binding region

We have recently isolated a neural tissue-specific syntaxin-1-binding prote in, named tomosyn, which is capable of dissociating Munc18/n-Sec1/rbSec1 fr om syntaxin-1 to form a 10S tomosyn complex, an intermediate complex conver ted to the 7S SNARE complex. We isolated here two splicing variants of tomo syn: one had 36 amino acids (aa) insertion and another had 17 aa deletion. We named original one m-tomosyn, big one b-tomosyn, and small one s-tomosyn . s-Tomosyn as web as m-tomosyn was mainly expressed in brain whereas b-tom osyn was ubiquitously expressed. All the isoforms bound to syntaxin-1, but not to syntaxin-2, -3, or -4, and had a region highly homologous to VAMP, a nother syntaxin-binding protein. This region was necessary but not sufficie nt for high-affinity binding of tomosyn to syntaxin-1. (C) 1999 Academic Pr ess.