The human Rhesus-associated RhAG protein and a kidney homologue promote ammonium transport in yeast.
The Rhesus blood-group antigens are defined by a complex association of membrane polypeptides that includes the non-glycosylated Rh proteins (RhD and RhCE) and the RHag glycoprotein, which is strictly required for cell surface expression of these antigens. RhAG and the Rh polypeptides are erythroid-specific transmembrane proteins belonging to the same family (36% identity). Despite their importance in transfusion medicine, the function of RhAG and Rh proteins remains unknown, except that their absence in Rh(null) individuals leads to morphological and functional abnormalities of erythrocytes, known as the Rh-deficiency syndrome. We recently found significant sequence similarity between the Rh family proteins, especially RhAG, and Mep/Amt ammonium transporters. We show here that RhAG and also RhGK, a new human homologue expressed in kidney cells only, function as ammonium transport proteins when expressed in yeast. Both specifically complement the growth defect of a yeast mutant deficient in ammonium uptake. Moreover, ammonium efflux assays and growth tests in the presence of toxic concentrations of the analogue methylammonium indicate that RhAG and RhGK also promote ammonium export. Our results provide the first experimental evidence for a direct role of RhAG and RhGK in ammonium transport. These findings are of high interest, because no specific ammonium transport system has been characterized so far in human.
Marini
A M
AM
Laboratoire de Physiologie Cellulaire, Université Libre de Bruxelles, Institut de Biologie et de Médecine Moléculaires, Gosselies, Belgium.
Matassi
G
G
Raynal
V
V
André
B
B
Cartron
J P
JP
Chérif-Zahar
B
B
D000818:Animals; D001798:Blood Proteins; D015153:Blotting, Western; D017173:Caenorhabditis elegans / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D027682:Cation Transport Proteins; D004331:Drosophila melanogaster / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005816:Genetic Complementation Test; D015801:Helminth Proteins / Q000378:metabolism; D006801:Humans; D019476:Insect Proteins / Q000378:metabolism; D017136:Ion Transport; D007668:Kidney / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology*; D008969:Molecular Sequence Data; D009928:Organ Specificity; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012204:Rh-Hr Blood-Group System / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013045:Species Specificity
D001798:Blood Proteins; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D005656:Fungal Proteins; D015801:Helminth Proteins; D019476:Insect Proteins; C088951:MEP1 protein, S cerevisiae; C107270:MEP2 protein, S cerevisiae; C107271:MEP3 protein, S cerevisiae; D008562:Membrane Glycoproteins; D000644:Quaternary Ammonium Compounds; C498523:RHAG protein, human; C413213:RHCG protein, human; D012204:Rh-Hr Blood-Group System; C485880:Rhcg protein, mouse; D029701:Saccharomyces cerevisiae Proteins