Synaptotagmin III is a novel isoform of rat synaptotagmin expressed in endocrine and neuronal cells.
Synaptotagmin (p65), an integral membrane protein of synaptic vesicles, is thought to be involved in calcium-dependent exocytosis of synaptic vesicles. Here, we report the cloning and tissue distribution of a novel isoform of synaptotagmin, designated synaptotagmin III. The cDNA clones encoding synaptotagmin III have been isolated from a rat brain cDNA library. Rat synaptotagmin III is a protein of 588 amino acids having 40.5, 38.3, and 64.0% identity with rat synaptotagmin I, rat synaptotagmin II, and o-p65-C, a third synaptotagmin isoform of marine ray Discopyge ommata, respectively. The region of the two internal repeats homologous to the regulatory domain (C2 domain) of protein kinase C is highly conserved among synaptotagmin I, II, and III. RNA blotting studies reveal that synaptotagmin III mRNA is expressed in brain, various endocrine tissues, and hormone-secreting clonal cells. These results suggest that rat synaptotagmin III is a mammalian homolog of o-p65-C and is involved in Ca(2+)-dependent exocytosis of secretory vesicles in endocrine cells, as well as in neurons.
Mizuta
M
M
Division of Molecular Medicine, Chiba University School of Medicine, Japan.
Inagaki
N
N
Nemoto
Y
Y
Matsukura
S
S
Takahashi
M
M
Seino
S
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D003001:Cloning, Molecular; D017931:DNA Primers; D004702:Endocrine Glands / Q000378:metabolism*; D005260:Female; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000096:biosynthesis*; D009474:Neurons / Q000378:metabolism*; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012860:Skates, Fish; D050863:Synaptotagmin I; D050857:Synaptotagmins
D002135:Calcium-Binding Proteins; D017931:DNA Primers; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D050863:Synaptotagmin I; C494312:Syt1 protein, rat; C494291:Syt3 protein, rat; D050857:Synaptotagmins