A Novel Isoform of Syntaxin-binding Protein Homologous to Yeast Sec1 Expressed Ubiquitously in Mammalian Cells

doi:10.1074/jbc.270.10.4963

A Novel Isoform of Syntaxin-binding Protein Homologous to Yeast Sec1 Expressed Ubiquitously in Mammalian Cells (*)

From the (1)Third Department of Internal Medicine and Department of Disease-related Gene Regulation Research (Sandoz), Faculty of Medicine, University of Tokyo, Hongo, Tokyo 113, Japan and the
(2)Institute for Adult Disease, Asahi Life Foundation, Nishishinjuku, Shinjuku, Tokyo 160, Japan

^§To whom correspondence should be addressed. Present address:
Third Dept. of Internal Medicine, Yamaguchi University School of Medicine, Kogushi 1144, Ube, Yamaguchi 755, Japan
. Fax: 81-836-22-2342. The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) D42068[GenBank].

Abstract

munc-18/n-Sec1/rbSec1, a brain homologue of the yeast Sec1p protein, is thought to participate in regulating the docking and fusion of synaptic vesicles. We have screened the mouse cDNA library of an MIN6 cell line, derived from pancreatic β cells, for its novel isoform and have identified a cDNA encoding a 593-amino acid protein having 63, 53, and 30% identity with munc-18/n-Sec1/rbSec1, Caenorhabditis elegans unc18, and Saccharomycescerevisiae Sec1p, respectively. While munc-18/n-Sec1/rbSec1 expression has been reported to be neural-specific, RNA blot analysis has revealed that the novel isoform, which we refer to as muSec1 (mammalian ubiquitous Sec1), is expressed ubiquitously. We have also identified mouse munc-18/n-Sec1/rbSec1 from the MIN6 cDNA library, indicating that different isoforms of a protein participating in vesicular transport exist in a single cell. muSec1 bound to glutathione S-transferase-syntaxin 1A and, although with lower affinity, to glutathione S-transferase-syntaxin 4 fusion protein. These findings suggest that muSec1 is, via its binding to the syntaxin family, involved in the protein trafficking from the Golgi apparatus to the plasma membrane and that the fundamental mechanisms of protein trafficking have been conserved from yeast through virtually all mammalian cells.

Footnotes

↵* This work was supported by a grant-in-aid for scientific research from the Ministry of Education, Science and Culture and also by a grant for diabetes research from the Ministry of Health and Welfare of Japan. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
¹ The abbreviations used are:

SNAP

soluble N-ethylmaleimide-sensitive factor attachment protein

SNARE

SNAP receptor

PCR

polymerase chain reaction

bp

base pair(s).
- Received November 15, 1994.
- Revision received December 28, 1994.