title: IgM antigen receptor complex contains phosphoprotein products of B29 and mb-1 genes.
abstract: Membrane immunoglobulin M (mIgM) and mIgD are major B-lymphocyte antigen receptors, which function by internalizing antigens for processing and presentation to T cells and by transducing essential signals for proliferation and differentiation. Although ligation of mIgM or mIgD results in rapid activation of a phospholipase C and a tyrosine kinase(s), these receptors have cytoplasmic tails of only three amino acid residues (Lys-Val-Lys), which seem ill suited for direct physical coupling with cytoplasmic signal transduction structures. In this report, we identify the alpha, beta, and gamma components of the mIgM-associated phosphoprotein complex, which may play a role in signal transduction. Proteolytic peptide mapping demonstrated that the IgM-alpha chain differs from Ig-beta and Ig-gamma. The chains were purified, and amino-terminal sequencing revealed identity with two previously cloned B-cell-specific genes. One component, IgM-alpha, is a product of the mb-1 gene, and the two additional components, Ig-beta and Ig-gamma, are products of the B29 gene. Immunoblotting analysis using rabbit antibodies prepared against predicted peptide sequences of each gene product confirmed the identification of these mIgM-associated proteins. The deduced sequence indicates that these receptor subunits lack inherent protein kinase domains but include common tyrosine-containing sequence motifs, which are likely sites of induced tyrosine phosphorylation.
authors.affiliation: National Jewish Center for Immunology and Respiratory Medicine, Department of Pediatrics, Denver, CO 80206.
authors.forename: K S
authors.initials: KS
authors.lastname: Campbell
authors.forename: E J
authors.initials: EJ
authors.lastname: Hager
authors.forename: R J
authors.initials: RJ
authors.lastname: Friedrich
authors.forename: J C
authors.initials: JC
authors.lastname: Cambier
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD; D001402:B-Lymphocytes / Q000166:cytology*; D015153:Blotting, Western; D051925:CD79 Antigens; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000737:chemistry*; D051379:Mice; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010750:Phosphoproteins / Q000737:chemistry*; D011947:Receptors, Antigen, B-Cell / Q000737:chemistry*
chemical_list: D015703:Antigens, CD; D051925:CD79 Antigens; C497882:Cd79a protein, mouse; C497884:Cd79b protein, mouse; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D011947:Receptors, Antigen, B-Cell