RhAG protein of the Rhesus complex is a CO₂channel in the human red cell membrane

Abstract

We have determined CO2 permeabilities, P(CO2), of red cells of normal human blood and of blood deficient in various blood group proteins by a previously described mass spectrometric technique. While P(CO2) of normal red cells is approximately 0.15 cm/s, we find in red blood cells (RBCs) lacking the Rh protein complex (Rh(null)) a significantly reduced P(CO2) of 0.07 cm/s +/-0.02 cm/s (P<0.02). This value is similar to the value we have reported previously for RBCs lacking aquaporin-1 protein (AQP-1(null)), suggesting that each of the Rh and AQP-1 proteins is responsible for approximately 1/2 of the normal CO2 permeability of the RBC membrane. Four other blood group deficiencies tested lack diverse membrane proteins but exhibit normal CO2 permeability. The CO2 pathway constituted by Rh proteins was inhibitable at pH(e)= 7.4 by NH4Cl with an I50 of approximately 10 mM corresponding to an I50 for NH3 of approximately 0.3 mM. The pathway independent of Rh proteins, presumably that constituted by AQP-1, was not inhibitable by NH4Cl/NH3. However, both pathways were strongly inhibited by DIDS, which accounts for the marked inhibitory effect of DIDS on normal P(CO2), while in contrast another AE1 inhibitor, DiBAC, does not inhibit P(CO2), although it markedly reduces P(HCO3-). We conclude that Rh protein, presumably the Rh-associated glycoprotein RhAG, possesses a gas channel that allows passage of CO2 in addition to NH3.

The hereditary stomatocytoses

“…9 RhAG is a member of the band 3 macrocomplex and there is evidence that in normal cells it may function as an ammonium transporter, and/or gas channel. 10,11 The mutations identified (Phe65Ser, Ile61Arg) occur in the predicted transmembrane span 2 of the protein and are thought to widen the pore, allowing passage of cations. 9 This condition is unusual, in that it is characterized by a large reduction or even absence of the membrane lipid raft protein, stomatin.…”

Alterations of red blood cell metabolome in overhydrated hereditary stomatocytosis

“…2 RhAG may function as an ammonium transporter and/or a gas channel. [3][4][5] When expressed in Xenopus laevis oocytes, the human wild-type RhAG induces a monovalent cation leak considerably enhanced when mutated RhAG transporters are expressed instead. 2 Among membrane abnormalities, OHSt RBCs display a sharp reduction or an absence of stomatin, 6 an integral RBC membrane protein.…”

4.1R-deficient human red blood cells have altered phosphatidylserine exposure pathways and are deficient in CD44 and CD47 glycoproteins

“…As mentioned above, CD47 forms part of the Rh-band 3 supercomplex of the human erythrocyte membrane which may function to regulate CO2 and bicarbonate transport. [24][25][26] CD47 is substantially diminished in p4.2-deficient erythrocytes, which are also deficient in major components of the Rh complex, thus it is likely that CD47 interacts directly with protein 4.2 in human erythrocyte membranes, which does not appear to be the case in mice. 15,17 The Rh-band 3 complex includes the RhAG2-Rh protein trimer, 27,28 CD47, ICAM-4 and band 3 dimers/tetramers.…”