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1 Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1689; and 2 Department of Animal Cell Biochemistry, A.N. Belozersky Institute of Physico-Chemical Biology, Building A, Moscow State University, 119899 Moscow, Russia
The electroneutral sodium bicarbonate cotransporter 3 (NBC3) coimmunoprecipitates from renal lysates with the vacuolar H+-ATPase. In renal type A and B intercalated cells, NBC3 colocalizes with the vacuolar H+-ATPase. The involvement of the COOH termini of NBC3 and the 56-kDa subunit of the proton pump in the interaction of these proteins was investigated. The intact and modified COOH termini of NBC3 and the 56-kDa subunit of the proton pump were synthesized, coupled to Sepharose beads, and used to pull down kidney membrane proteins. Both the 56- and the 70-kDa subunits of the proton pump, as well as a PDZ domain containing protein Na+/H+ exchanger regulatory factor 1 (NHERF-1), were bound to the intact 18 amino acid NBC3 COOH terminus. A peptide truncated by five COOH-terminal amino acids did not bind these proteins. Replacement of the COOH-terminal leucine with glycine blocked binding of both the proton pump subunits but did not affect binding of NHERF-1. The 18 amino acid COOH terminus of the 56-kDa subunit of the proton pump bound NHERF-1 and NBC3, but the truncated and modified peptide did not. A complex of NBC3, the 56-kDa subunit of the proton pump, and NHERF-1 was identified in rat kidney. The data indicate that the COOH termini of NBC3 and the 56-kDa subunit of the vacuolar proton pump are PDZ-interacting motifs that are necessary for the interaction of these proteins. NHERF-1 is involved in the interaction of NBC3 and the vacuolar proton pump.
sodium; bicarbonate; cotransporters; membrane; binding
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