A novel isoform of syntaxin-binding protein homologous to yeast Sec1 expressed ubiquitously in mammalian cells.
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 beta 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 Saccharomyces cerevisiae 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.
Katagiri
H
H
Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Terasaki
J
J
Murata
T
T
Ishihara
H
H
Ogihara
T
T
Inukai
K
K
Fukushima
Y
Y
Anai
M
M
Kikuchi
M
M
Miyazaki
J
J
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D017124:Conserved Sequence; D017931:DNA Primers; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000737:chemistry; D015870:Gene Expression; D015723:Gene Library; D007515:Islets of Langerhans / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins / Q000096:biosynthesis* / Q000737:chemistry; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D050765:Qa-SNARE Proteins; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D033921:Vesicular Transport Proteins
D017931:DNA Primers; D005656:Fungal Proteins; D008565:Membrane Proteins; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; C497931:SEC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C497941:Stxbp2 protein, mouse; D033921:Vesicular Transport Proteins