title: Erythrocyte Mr 28,000 transmembrane protein exists as a multisubunit oligomer similar to channel proteins.
abstract: A novel Mr 28,000 erythrocyte transmembrane protein was recently purified and found to exist in two forms, "28kDa" and "gly28kDa," the latter containing N-linked carbohydrate (Denker, B. M., Smith, B. L., Kuhajda, F. P., and Agre, P. (1988) J. Biol. Chem. 263, 15634-15642). Although 28kDa protein resembles the Rh polypeptides biochemically, structural homologies were not identified by immunoblot or two-dimensional iodopeptide maps. The NH2-terminal amino acid sequence for the first 35 residues of purified 28kDa protein is 37% identical to the 26-kDa major intrinsic protein of lens (Gorin, M. B., Yancey, S. B., Cline, J., Revel, J.-P., and Horwitz, J. Cell 39, 49-59). Antisera to a synthetic peptide corresponding to the NH2-terminus of 28kDa protein gave a single reaction of molecular mass 28kDa on immunoblots of erythrocyte membranes. Selective digestions of intact erythrocytes and inside-out membrane vesicles with carboxypeptidase Y indicated the existence of a 5-kDa COOH-terminal cytoplasmic domain. Multiple studies indicated that 28kDa and gly28kDa proteins exist together as a multisubunit oligomer: 1) similar partial solubilizations in Triton X-100; 2) co-purification during ion exchange and lectin affinity chromatography; 3) cross-linking in low concentrations of glutaraldehyde; and 4) physical analyses of purified proteins and solubilized membranes in 1% (v/v) Triton X-100 showed 28kDa and gly28kDa proteins behave as a large single unit with Stokes radius of 61 A and sedimentation coefficient of 5.7 S. These studies indicate that the 28kDa and gly28kDa proteins are distinct from the Rh polypeptides and exist as a multisubunit oligomer. The 28kDa protein has NH2-terminal amino acid sequence homology and membrane organization similar to major intrinsic protein and other members of a newly recognized family of transmembrane channel proteins.
authors.affiliation: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
authors.forename: B L
authors.initials: BL
authors.lastname: Smith
authors.forename: P
authors.initials: P
authors.lastname: Agre
mesh_terms: D000595:Amino Acid Sequence; D001798:Blood Proteins / Q000737:chemistry* / Q000235:genetics; D015153:Blotting, Western; D002846:Chromatography, Affinity; D002918:Chymotrypsin; D003432:Cross-Linking Reagents; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000737:chemistry*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016415:Sequence Alignment; D014357:Trypsin
chemical_list: D001798:Blood Proteins; D003432:Cross-Linking Reagents; D008565:Membrane Proteins; C068043:erythrocyte transmembrane protein 28kDa, human; D002918:Chymotrypsin; D014357:Trypsin