VAT-1 from Torpedo electric organ forms a high-molecular-mass protein complex within the synaptic vesicle membrane.
VAT-1 is an abundant 41-kDa protein from Torpedo cholinergic synaptic vesicles. Most of VAT-1 immunoreactivity (70%) is localized to the synaptic vesicle membrane while the rest (30%) copurifies with larger membranous fragments. VAT-1 forms a high-molecular-mass complex within the synaptic vesicle membrane. The Stokes radius of the VAT-1 complex is 4.85 nm and the sedimentation coefficient is 8.0 x 10(-13) S. Using these values, the calculated apparent mass of the VAT-1 complex is 176 kDa and the friction coefficient is consistent with that for a globular protein. Electrophoresis of solubilized synaptic vesicle proteins following cross-linking resulted in a 40-kDa ladder which was detected by VAT-1 antibodies. This is in accord with VAT-1 protein complex being composed primarily of VAT-1 subunits. The hydrodynamic characteristics of the VAT-1 protein complex suggest that it is composed of three or four VAT-1 subunits. Synaptophysin, an abundant component of Torpedo synaptic vesicle membranes, which has a similar apparent size as VAT-1, is not part of the VAT-1 protein complex. Interactions between the subunits within the protein complex do not depend on disulfide bonds or on lowering the ionic strength. However, partial dissociation of VAT-1 subunits from the complex occurs by chelating calcium ions.
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Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Israel.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002850:Chromatography, Gel; D004220:Disulfides; D004557:Electric Organ / Q000737:chemistry; D015151:Immunoblotting; D008565:Membrane Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D016622:Silver Staining; D013572:Synaptic Vesicles / Q000737:chemistry / Q000378:metabolism*; D016708:Synaptophysin / Q000032:analysis / Q000737:chemistry; D014101:Torpedo
D004220:Disulfides; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D016708:Synaptophysin; C063277:VAT-1 protein, Torpedo; D002118:Calcium