title: Rab3a interacting molecule (RIM) and the tethering of pre-synaptic transmitter release site-associated CaV2.2 calcium channels.
abstract: Biochemical and physiological evidence suggest that pre-synaptic calcium channels are attached to the transmitter release site within the active zone by a molecular tether. A recent study has proposed that 'Rab3a Interacting Molecule' (RIM) serves as the tether for CaV2.1 channels in mouse brain, based in part on biochemical co-immunoprecipitation (co-IP) using a monoclonal antibody, mRIM. We previously argued against this idea for CaV2.2 calcium channel at chick synapses based on experiments using a different anti-RIM antibody, pRIM1,2: while staining for the two proteins co-localized and co-varied at the transmitter release face, consistent with an association, they failed to co-IP from a synaptosome membrane lysate. RIM is, however, a family of proteins and we tested the possibility that the mRIM antibody used in the more recent study identifies a particular channel-tethering variant. We find that co-immunostaining with mRIM and anti-CaV2.2 antibody neither co-localized nor co-varied at the transmitter release face and the two proteins did not co-IP, arguing against a common protein complex and a key CaV2.2 scaffolding role for RIM at the active zone. The differing results might be reconciled, however, in a model where a RIM family member contributes to a protein bridge that anchors the pre-fusion secretory vesicle to the calcium channel protein complex.
authors.affiliation: Laboratory of Synaptic Transmission, Toronto Western Research Institute, Toronto Ontario, Canada.
authors.forename: Fiona K
authors.initials: FK
authors.lastname: Wong
authors.forename: Elise F
authors.initials: EF
authors.lastname: Stanley
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D020864:Calcium Channels, N-Type / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D019204:GTP-Binding Proteins / Q000378:metabolism; D005728:Ganglia, Sympathetic / Q000166:cytology; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D013574:Synaptosomes / Q000378:metabolism; D014162:Transfection / Q000379:methods; D020826:rab3A GTP-Binding Protein / Q000378:metabolism*
chemical_list: C503279:Cacna1b protein, rat; D020864:Calcium Channels, N-Type; D009419:Nerve Tissue Proteins; C491490:Rims1 protein, mouse; C484282:Rims2 protein, rat; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D019204:GTP-Binding Proteins; D020826:rab3A GTP-Binding Protein