Synaptotagmins in membrane traffic: which vesicles do the tagmins tag?
The aim of this review is to give a broad picture of what is actually known about the synaptotagmin family. Synaptotagmin I is an abundant synaptic vesicle and secretory granule protein in neurons and endocrine cells which plays a key role in Ca(2+)-induced exocytosis. It belongs to the large family of C2 domain-proteins as it contains two internal repeats that have homology to the C2 domain of protein kinase C. Eleven synaptotagmin genes have been described in rat and mouse. Except for synaptotagmin I, and by analogy synaptotagmin II, the functions of these proteins are unknown. In this review we focus on data obtained on the various isoforms without exhaustively discussing the role of synaptotagmin I in neurotransmission. Numerous in vitro interactions of synaptotagmin I with key components of the exocytosis-endocytosis machinery have been reported. Additional data concerning the other synaptotagmins are now becoming available and are reviewed here. Only interactions which have been described for several synaptotagmins, are mentioned. It is unlikely that a single isoform displays all of these potential interactions in vivo and probably the subcellular distribution of the protein will favor some of them and preclude others. Therefore, to discuss the putative role of the various synaptotagmins we have examined in detail published data concerning their localization.
Marquèze
B
B
INSERM U464, Institut Fédératif Jean-Roche, Université de la Méditerranée, Faculté de Médecine, Boulevard Pierre-Dramard, 13916 cedex 20, Marseille, France. marqueze@jean-roche.univ-mrs.fr
Berton
F
F
Seagar
M
M
D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism*; D005089:Exocytosis; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009490:Neurosecretory Systems / Q000502:physiology; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D013572:Synaptic Vesicles / Q000378:metabolism*; D050863:Synaptotagmin I; D050857:Synaptotagmins
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D050863:Synaptotagmin I; D050857:Synaptotagmins