Clathrin‐Coated Vesicle Subtypes in Mammalian Brain Tissue: Detection of Polypeptide Heterogeneity by Immunoprecipitation with Monoclonal Antibodies

Abstract: A panel of monoclonal antibodies (mAbs) was developed to identify polypeptides sorted in subtypes of brain coated vesicles (CVs) and to separate these by immunoprecipitation. The corresponding antigen of some of the mAbs elicited by CV components was present also in synaptosomal plasma membrane, synaptic vesicles, or microsomes. On im‐munoblots the mAbs reacted with constitutive brain CV proteins, with cargo molecules, and with a novel CV component that interacts with the actin cytoskeleton. Analysis of radio‐iodinated brain CVs immunoprecipitated with a tubulin antibody revealed that all brain CVs contained tubulin. The mAb A‐7C11 recognized a 40‐kilodalton (kDa) polypeptide on the clathrin coat and immunoprecipitated one‐quarter of the total brain CVs. The mAb S‐l1 D9 reacted with a 44‐kDa antigen and immunoprecipitated 25% of the CVs. This antigen (44 kDa) was present in synaptic vesicles and synaptosomal membrane as well. Moreover, this mAb (S‐11 D9) reacted with a polypeptide of 56 kDa detected only in synaptosomal membrane. A mAb (C‐10B2) that reacted with one of the clathrin light chains (LC_b) immunoprecipitated 90% of the brain CVs. One of the mAbs immunoprecipitated a CV subtype that displayed a reversed ratio of the clathrin LCs (LC_a > LC_b). Each of the mAbs yielded different im‐munofluorescent staining patterns of vesicles in culture cell types that included nerve growth factor‐differentiated PC 12 cells, neuroblastoma cells, and Madin Darby bovine kidney cells. The data suggest that in brain tissue there is a heterogeneous population of CVs with different polypeptide compositions and subcellular distributions and that each of these subtypes performs a different role in nerve cells.