Functional analysis and molecular modeling of a cloned urate transporter/channel.
Recombinant protein, designated UAT, prepared from a cloned rat renal cDNA library functions as a selective voltage-sensitive urate transporter/channel when fused with lipid bilayers. Since we previously suggested that UAT may represent the mammalian electrogenic urate transporter, UAT has been functionally characterized in the presence and absence of potential channel blockers, several of which are known to block mammalian electrogenic urate transport. Two substrates, oxonate (a competitive uricase inhibitor) and pyrazinoate, that inhibit renal electrogenic urate transport also block UAT activity. Of note, oxonate selectively blocks from the cytoplasmic side of the channel while pyrazinoate only blocks from the channel's extracellular face. Like oxonate, anti-uricase (an electrogenic transport inhibitor) also selectively blocks channel activity from the cytoplasmic side. Adenosine blocks from the extracellular side exclusively while xanthine blocks from both sides. These effects are consistent with newly identified regions of homology to uricase and the adenosine A1/A3 receptor in UAT and localize these homologous regions to the cytoplasmic and extracellular faces of UAT, respectively. Additionally, computer analyses identified four putative alpha-helical transmembrane domains, two beta sheets, and blocks of homology to the E and B loops of aquaporin-1 within UAT. The experimental observations substantiate our proposal that UAT is the molecular representation of the renal electrogenic urate transporter and, in conjunction with computer algorithms, suggest a possible molecular structure for this unique channel.
Leal-Pinto
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E
Division of Nephrology, Department of Medicine, Mount Sinai School of Medicine, Box #1243, One Gustave L. Levy Place, New York, NY 10029, USA.
Cohen
B E
BE
Abramson
R G
RG
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D002417:Cattle; D003001:Cloning, Molecular; D008051:Lipid Bilayers / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D027361:Organic Anion Transporters; D010094:Oxonic Acid / Q000378:metabolism; D011718:Pyrazinamide / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D018047:Receptors, Purinergic P1 / Q000032:analysis; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D014503:Urate Oxidase / Q000378:metabolism; D014527:Uric Acid / Q000378:metabolism*; D019820:Xanthine / Q000378:metabolism
D002352:Carrier Proteins; C491242:Lgals9 protein, rat; D008051:Lipid Bilayers; D027361:Organic Anion Transporters; D018047:Receptors, Purinergic P1; C103862:urate transporter; D019820:Xanthine; D014527:Uric Acid; D011718:Pyrazinamide; C005296:pyrazinoic acid; D010094:Oxonic Acid; D014503:Urate Oxidase