Expression and localization of synaptotagmin I in rat parotid gland.
Synaptotagmins are a gene family of membrane proteins with distinct expression patterns. Synaptotagmin I is an abundant protein of the synaptic vesicle membrane and was implicated as the Ca2+ sensor in fast responding synapses. Yet, its precise role along the synaptic vesicle life cycle is not fully understood. In this report we show that synaptotagmin I is not exclusively confined to neuronal and neuroendocrine systems, rather, it is also expressed in the exocrine system of the parotid gland. The gene for synaptotagmin I was isolated and sequenced from rat parotid cDNA. The identity of synaptotagmin I protein was further confirmed by several independent antibodies. The protein is exclusively found in the membranous fraction of purified granules, similarly to VAMP-2, another major integral membrane protein of synaptic vesicles. Synaptotagmin I represents 0.4% of the total membrane protein mass of the granule. Using immunoelectron microscopy the two proteins were also localized primarily to the granules' membranes. These findings suggest that synaptotagmin I which regulates Ca(2+)-dependent neurotransmitter release also plays a role which is common to all secretory organelles-neuronal, endocrine and exocrine. A role for synaptotagmin I in integrating signals with protein secretion in the parotid gland is suggested.
Levius
O
O
Department of Biological Chemistry, University of Jerusalem, Israel.
Feinstein
N
N
Linial
M
M
D000818:Animals; D002135:Calcium-Binding Proteins; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D004792:Enzyme Precursors / Q000737:chemistry / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000201:enzymology / Q000648:ultrastructure; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D050683:R-SNARE Proteins; D012333:RNA, Messenger / Q000737:chemistry / Q000302:isolation & purification; D051381:Rats; D017207:Rats, Sprague-Dawley; D050863:Synaptotagmin I; D050857:Synaptotagmins; D014158:Transcription, Genetic
D002135:Calcium-Binding Proteins; D004792:Enzyme Precursors; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050683:R-SNARE Proteins; D012333:RNA, Messenger; D050863:Synaptotagmin I; C494312:Syt1 protein, rat; D050857:Synaptotagmins