Transport characteristics of mammalian Rh and Rh glycoproteins expressed in heterologous systems.
The development and use of heterologous expression systems is critical for deciphering the function of mammalian Rh and Rh-glycoproteins. The studies here use Xenopus oocytes, well known for their ability to readily traffic and express difficult membrane proteins, and S. cerevisiae wild-type strains and mutants that are defective in ammonium transport. Data obtained in both of these expression systems revealed that mammalian Rh-glycoprotein-mediated transport (RhAG, RhBG, and RhCG) is an electroneutral process that is driven by the NH4+ concentration and the transmembrane H+ gradient, effectively exchanging NH4+ for H+ in a process that results in transport of net NH3. Homology modeling and functional studies suggest that the more recently evolved erythrocyte blood group proteins, RhCE and RhD, may not function directly in ammonia transport and may be evolving a new function in the RBC membrane. The relationship of Rh and Rh-glycoproteins to the Amt/Mep ammonium transporters is substantiated with functional transport data and structural modeling.
American Red Cross, 700 Spring Garden, Philadelphia, PA 19130, USA. westhoff@mail.med.upenn.edu
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D000818:Animals; D001692:Biological Transport; D001798:Blood Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry; D005260:Female; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008744:Methylamines / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D009865:Oocytes / Q000378:metabolism*; D009994:Osmolar Concentration; D011487:Protein Conformation; D011522:Protons; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012204:Rh-Hr Blood-Group System / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013329:Structure-Activity Relationship; D014162:Transfection; D014982:Xenopus laevis
C111096:AmtB protein, E coli; D001798:Blood Proteins; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D006023:Glycoproteins; C088951:MEP1 protein, S cerevisiae; C107270:MEP2 protein, S cerevisiae; C107271:MEP3 protein, S cerevisiae; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008744:Methylamines; D011522:Protons; C498523:RHAG protein, human; C066468:RHCE protein, human; D011993:Recombinant Fusion Proteins; D012204:Rh-Hr Blood-Group System; C486033:RhBG protein, mouse; C485880:Rhcg protein, mouse; D029701:Saccharomyces cerevisiae Proteins; C027451:methylamine