Rh type B glycoprotein is a new member of the Rh superfamily and a putative ammonia transporter in mammals.
Ammonium transporters play a key functional role in nitrogen uptake and assimilation in microorganisms and plants; however, little is known about their structural counterpart in mammals. Here, we report the molecular cloning and biochemical characterization of Rh type B glycoproteins, human RhBG and mouse Rhbg, two new members of the Rh family with distinct tissue specificities. The RhBG orthologues possess a conserved 12-transmembrane topology and most resemble bacterial and archaeal ammonium transporters. Human RHBG resides at chromosome 1q21.3, which harbors candidate genes for medullary cystic kidney disease, whereas mouse Rhbg is syntenic on chromosome 3. Northern blot and in situ hybridization revealed that RHBG and Rhbg are predominantly expressed in liver, kidney, and skin, the specialized organs involving ammonia genesis, excretion, or secretion. Confocal microscopy showed that RhBG is located in the plasma membrane and in some intracellular granules. Western blots of membrane proteins from stable HEK293 cells and from mouse kidney and liver confirmed this distribution. N-Glycanase digestion showed that RhBG/Rhbg has a carbohydrate moiety probably attached at the NHS motif on exoloop 1. Phylogenetic clustering, tissue-specific expression, and plasma membrane location suggest that RhBG homologous proteins are the long sought major ammonium transporters in mammalians.
Liu
Z
Z
Laboratory of Biochemistry and Molecular Genetics, Lindsley F. Kimball Research Institute, New York Blood Center, New York, New York 10021 , USA.
Peng
J
J
Mo
R
R
Hui
C
C
Huang
C H
CH
D000595:Amino Acid Sequence; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001798:Blood Proteins; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D027682:Cation Transport Proteins; D002874:Chromosome Mapping; D002878:Chromosomes, Human, Pair 1; D005819:Genetic Markers; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008322:Mammals; D008562:Membrane Glycoproteins / Q000737:chemistry; D026901:Membrane Transport Proteins; D051379:Mice; D008969:Molecular Sequence Data; D010802:Phylogeny; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012867:Skin / Q000378:metabolism
D001798:Blood Proteins; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D005819:Genetic Markers; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; C498523:RHAG protein, human; C422995:RHBG protein, human; C413213:RHCG protein, human; C486033:RhBG protein, mouse; C401210:Rhag protein, mouse; C485880:Rhcg protein, mouse; D000641:Ammonia