SV2B regulates synaptotagmin 1 by direct interaction.
SV2 proteins are abundant synaptic vesicle proteins expressed in two major (SV2A and SV2B) and one minor (SV2C) isoform. SV2A and SV2B have been shown to be involved in the regulation of synaptic vesicle exocytosis. Previous studies found that SV2A, but not SV2B, can interact with the cytoplasmic domain of synaptotagmin 1, a Ca2+ sensor for synaptic vesicle exocytosis. To determine whether SV2B can interact with full-length synaptotagmin 1, we performed immunoprecipitations from brain protein extracts and found that SV2B interacts strongly with synaptotagmin 1 in a detergent-resistant, Ca2+ -independent manner. In contrast, an interaction between native SV2A and synaptotagmin 1 was not detectable under these conditions. The SV2B-synaptotagmin 1 complex also contained the synaptic t-SNARE proteins, syntaxin 1 and SNAP-25, suggesting that SV2B may participate in exocytosis by modulating the interaction of synaptotagmin 1 with t-SNARE proteins. Analysis of retinae in SV2B knock-out mice revealed a strong reduction in the level of synaptotagmin 1 in rod photoreceptor synapses, which are unique in that they express only the SV2B isoform. In contrast, other synaptic vesicle proteins were not affected by SV2B knock out, indicating a specific role for SV2B in the regulation of synaptotagmin 1 levels at certain synapses. These experiments suggest that the SV2B-synaptotagmin 1 complex is involved in the regulation of synaptotagmin 1 stability and/or trafficking. This study has demonstrated a new role of SV2B as a regulator of synaptotagmin 1 that is likely mediated by direct interaction of these two synaptic proteins.
WM Keck Center for Learning and Memory, Department of Neurobiology and Anatomy, University of Texas Medical School, Houston, Texas 77030, USA.
Diana R
DR
Lazzell
Roger
R
Belizaire
Pratima
P
Thakur
David M
DM
Sherry
Roger
R
Janz
D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005089:Exocytosis; D006801:Humans; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism; D050600:SNARE Proteins; D013572:Synaptic Vesicles / Q000378:metabolism; D050863:Synaptotagmin I; D050857:Synaptotagmins; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins / Q000378:metabolism
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; D050600:SNARE Proteins; C494212:STX1A protein, human; C494310:SYT1 protein, human; C494214:Stx1a protein, mouse; C489615:Sv2b protein, mouse; D050863:Synaptotagmin I; D050827:Syntaxin 1; C494311:Syt1 protein, mouse; D033921:Vesicular Transport Proteins; D050857:Synaptotagmins; D002118:Calcium