title: An integral membrane protein antigen associated with the membrane attachment sites of actin microfilaments is identified as an integrin beta-chain.
abstract: A monoclonal antibody (MAb 30B6) was recently described by Rogalski and Singer (J. Cell Biol. 101:785-801, 1985) which identified an integral membrane glycoprotein of chicken cells that was associated with a wide variety of sites of actin microfilament attachments to membranes. In this report, we present a further characterization of this integral protein. An immunochemical comparison was made of MAb 30B6 binding properties with those of two other MAbs, JG9 and JG22, which identify a component of a membrane protein complex that interacts with extracellular matrix proteins including fibronectin. We showed that the 110-kilodalton protein recognized by MAb 30B6 in extracts of chicken gizzard smooth muscle is identical, or closely related, to the protein that reacts with MAbs JG9 and JG22. These 110-kilodalton proteins are also structurally closely similar, if not identical, to one another as demonstrated by 125I-tryptic peptide maps. However, competition experiments showed that MAb 30B6 recognizes a different epitope from those recognized by MAbs JG9 and JG22. In addition, the 30B6 antigen is part of a complex that can be isolated on fibronectin columns. These results together establish that the 30B6 antigen is the same as, or closely similar to, the beta-chain of the protein complex named integrin, which is the complex on chicken fibroblast membranes that binds fibronectin. Although the 30B6 antigen is present in a wide range of tissues, its apparent molecular weight on gels varies in different tissues. These differences in apparent molecular weight are due, in large part, to differences in glycosylation.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex / Q000032:analysis; D000954:Antigens, Surface / Q000032:analysis*; D002478:Cells, Cultured; D002642:Chick Embryo; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes / Q000032:analysis; D006026:Glycoside Hydrolases; D016023:Integrins; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D000199:Actins; D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D000954:Antigens, Surface; D000939:Epitopes; D016023:Integrins; D008562:Membrane Glycoproteins; D006026:Glycoside Hydrolases