title: Human transcobalamin II receptor binds to Staphylococcus aureus protein A: implications as to its structure and function.
abstract: Purified human placental transcobalamin II receptor (TC II-R) dimer of molecular mass 124 kDa bound to Sepharose-linked bacterial immunoglobulin (IgG) binding proteins protein A, protein G, and protein A/G. TC II-R dimer was detected directly, by blotting human placental and rabbit and rat kidney membrane proteins with 125I-protein A, or indirectly, using antiserum to TC II-R or IgG-Fc region and 125I-protein. TC II-R antiserum, but not protein A, protein G, protein A/G, or antiserum to the IgG-Fc region, when added to culture medium of human intestinal epithelial Caco-2 cells or umbilical vein endothelial cells, inhibited ligand binding. However, protein A, protein G, protein A/G, or antiserum to the Fc region inhibited the internalization of the ligand TC II-[57Co]cyanocobalamin. Taken together, these studies strongly suggest TC II-R is an IgG-like molecule that contains an Fc-like region which is important in ligand internalization but not binding.
authors.affiliation: Gastroenterology and Hepatology Division, Department of Medicine, Milwaukee, Wisconsin 53295, USA.
authors.forename: Sravan K
authors.initials: SK
authors.lastname: Vanamala
authors.forename: Shakuntla
authors.initials: S
authors.lastname: Seetharam
authors.forename: Raghunatha R
authors.initials: RR
authors.lastname: Yammani
authors.forename: Bellur
authors.initials: B
authors.lastname: Seetharam
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003429:Cross Reactions; D019281:Dimerization; D004730:Endothelium, Vascular / Q000166:cytology; D005260:Female; D006801:Humans; D007106:Immune Sera / Q000494:pharmacology; D007141:Immunoglobulin Fc Fragments / Q000276:immunology; D007074:Immunoglobulin G / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D008024:Ligands; D010920:Placenta / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D011817:Rabbits; D051381:Rats; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000378:metabolism*; D013205:Staphylococcal Protein A / Q000737:chemistry / Q000378:metabolism*; D014471:Umbilical Veins / Q000166:cytology; D014805:Vitamin B 12 / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C034284:IgG Fc-binding protein, Streptococcus; D007106:Immune Sera; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D008024:Ligands; D011956:Receptors, Cell Surface; D013205:Staphylococcal Protein A; C028176:transcobalamin receptor; D014805:Vitamin B 12