title: Distinct regions of human glycophorin A enhance human red cell anion exchanger (band 3; AE1) transport function and surface trafficking.
abstract: Human red cell glycophorin A (GPA) enhances the expression of band 3 anion transport activity at the cell surface of Xenopus oocytes. This effect of GPA could occur in two ways, enhancement of band 3 anion transport function or enhancement of band 3 trafficking to the cell surface. We have examined the GPA effect using GPA mutants. We compared the sequences of GPA and its homolog glycophorin B (GPB; which does not facilitate band 3 cell-surface activity or trafficking) to identify candidate regions of GPA for study. We constructed several GPA or GPB mutants, including naturally occurring GPA/GPB hybrid molecules and insertion, deletion, and substitution mutants. We analyzed the effects of the mutant proteins on band 3-specific chloride transport and surface presentation using co-expression in Xenopus oocytes. We find that the C-terminal cytoplasmic tail of GPA enhances trafficking of band 3 to the cell surface, whereas the extracellular residues 68-70 increase the specific anion transport activity of band 3. In addition, examination of the oligomerization of GPA mutants showed that single amino acid substitutions N-terminal to the transmembrane domain greatly reduce SDS-stable GPA dimer formation, implying that regions outside the transmembrane domain of GPA are important for GPA dimer formation.
authors.affiliation: Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom. mty24@totalise.co.uk
authors.forename: Mark T
authors.initials: MT
authors.lastname: Young
authors.forename: Michael J A
authors.initials: MJ
authors.lastname: Tanner
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000737:chemistry* / Q000378:metabolism; D000838:Anions; D001692:Biological Transport; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002474:Cell-Free System; D002713:Chlorine / Q000378:metabolism; D002918:Chymotrypsin / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D006021:Glycophorins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D018075:RNA, Complementary / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D014981:Xenopus
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D000838:Anions; D006021:Glycophorins; D018075:RNA, Complementary; D002713:Chlorine; D012313:RNA; D002918:Chymotrypsin