Stomatin modulates the activity of the Anion Exchanger 1 (AE1, SLC4A1).

Anion Exchanger 1 (AE1) and stomatin are integral proteins of the red blood cell (RBC) membrane. Erythroid and kidney AE1 play a major role in HCO and Cl exchange. Stomatins down-regulate the activity of many channels and transporters.

Evidence of a structural and functional ammonium transporter RhBG·anion exchanger 1·ankyrin-G complex in kidney epithelial cells.

The renal ammonium transporter RhBG and anion exchanger 1 kAE1 colocalize in the basolateral domain of α-intercalated cells in the distal nephron. Although we have previously shown that RhBG is linked to the spectrin-based skeleton through ankyrin-G and that its NH3 transport activity is dependent on this association, there is no evidence for an interaction of kAE1 with this adaptor protein. We report here that the kAE1 cytoplasmic N terminus actually binds to ankyrin-G, both in yeast two-hybrid analysis and by coimmunoprecipitation in situ in HEK293 cells expressing recombinant kAE1.

Rapid Cl⁻/HCO⁻₃exchange kinetics of AE1 in HEK293 cells and hereditary stomatocytosis red blood cells.

Anion exchanger 1 (AE1) or band 3 is a membrane protein responsible for the rapid exchange of chloride for bicarbonate across the red blood cell membrane. Nine mutations leading to single amino-acid substitutions in the transmembrane domain of AE1 are associated with dominant hereditary stomatocytosis, monovalent cation leaks, and reduced anion exchange activity. We set up a stopped-flow spectrofluorometry assay coupled with flow cytometry to investigate the anion transport and membrane expression characteristics of wild-type recombinant AE1 in HEK293 cells, using an inducible expression system.

Phosphorylation and ankyrin-G binding of the C-terminal domain regulate targeting and function of the ammonium transporter RhBG.

RhBG, a human member of the Amt/Mep/Rh/superfamily of ammonium transporters, has been shown to facilitate NH(3) transport and to be anchored to the basolateral plasma membrane of kidney epithelial cells, via ankyrin-G. We showed here that triple alanine substitution of the (419)FLD(421) sequence, which links the cytoplasmic C-terminal domain of RhBG to ankyrin-G, not only disrupted the interaction of RhBG with the spectrin-based skeleton but also delayed its cell surface expression, decreased its plasma membrane stability, and abolished its NH(3) transport function in epithelial cell lines. Similarly, we demonstrated that both anchoring to the membrane skeleton and ammonium transport activity are regulated by the phosphorylation status of the C-terminal tail of RhBG.

Different transport mechanisms in plant and human AMT/Rh-type ammonium transporters.

The conserved family of AMT/Rh proteins facilitates ammonium transport across animal, plant, and microbial membranes. A bacterial homologue, AmtB, forms a channel-like structure and appears to function as an NH3 gas channel. To evaluate the function of eukaryotic homologues, the human RhCG glycoprotein and the tomato plant ammonium transporter LeAMT1;2 were expressed and compared in Xenopus oocytes and yeast.

Human Rhesus B and Rhesus C glycoproteins: properties of facilitated ammonium transport in recombinant kidney cells.

The mammalian Rh (Rhesus) protein family belongs to the Amt/Mep (ammonia transporter/methylammonium permease)/Rh superfamily of ammonium transporters. Whereas RhCE, RhD and RhAG are erythroid specific, RhBG and RhCG are expressed in key organs associated with ammonium transport and metabolism. We have investigated the ammonium transport function of human RhBG and RhCG by comparing intracellular pH variation in wild-type and transfected HEK-293 (human embryonic kidney) cells and MDCK (Madin-Darby canine kidney) cells in the presence of ammonium (NH4+/NH3) gradients.

The ammonium transporter RhBG: requirement of a tyrosine-based signal and ankyrin-G for basolateral targeting and membrane anchorage in polarized kidney epithelial cells.

RhBG is a nonerythroid member of the Rhesus (Rh) protein family, mainly expressed in the kidney and belonging to the Amt/Mep/Rh superfamily of ammonium transporters. The epithelial expression of renal RhBG is restricted to the basolateral membrane of the connecting tubule and collecting duct cells. We report here that sorting and anchoring of RhBG to the basolateral plasma membrane require a cis-tyrosine-based signal and an association with ankyrin-G, respectively.

RhBG and RhCG, the putative ammonia transporters, are expressed in the same cells in the distal nephron.

Two nonerythroid homologs of the blood group Rh proteins, RhCG and RhBG, which share homologies with specific ammonia transporters in primitive organisms and plants, could represent members of a new family of proteins involved in ammonia transport in the mammalian kidney. Consistent with this hypothesis, the expression of RhCG was recently reported at the apical pole of all connecting tubule (CNT) cells as well as in intercalated cells of collecting duct (CD). To assess the localization along the nephron of RhBG, polyclonal antibodies against the Rh type B glycoprotein were generated.