Functional analysis and molecular model of the human urate transporter/channel, hUAT.
Recombinant protein, designated hUAT, the human homologue of the rat urate transporter/channel (UAT), functions as a highly selective urate channel in lipid bilayers. Functional analysis indicates that hUAT activity, like UAT, is selectively blocked by oxonate from its cytosolic side, whereas pyrazinoate and adenosine selectively block from the channel's extracellular face. Importantly, hUAT is a galectin, a protein with two beta-galactoside binding domains that bind lactose. Lactose significantly increased hUAT open probability but only when added to the channel's extracellular side. This effect on open probability was mimicked by glucose, but not ribose, suggesting a role for extracellular glucose in regulating hUAT channel activity. These functional observations support a four-transmembrane-domain structural model of hUAT, as previously predicted from the primary structure of UAT. hUAT and UAT, however, are not functionally identical: hUAT has a significantly lower single-channel conductance and open probability is voltage independent. These differences suggest that evolutionary changes in specific amino acids in these highly homologous proteins are functionally relevant in defining these biophysical properties.
Leal-Pinto
Edgar
E
Division of Nephrology, Department of Medicine, Mount Sinai School of Medicine, New York, New York, 10029, USA.
Cohen
B Eleazar
BE
Lipkowitz
Michael S
MS
Abramson
Ruth G
RG
D000241:Adenosine / Q000494:pharmacology; D000595:Amino Acid Sequence; D001665:Binding Sites; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006021:Glycophorins / Q000235:genetics; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D007785:Lactose / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008958:Models, Molecular; D008969:Molecular Sequence Data; D027361:Organic Anion Transporters; D027701:Organic Cation Transport Proteins; D010094:Oxonic Acid / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D011718:Pyrazinamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D012266:Ribose / Q000494:pharmacology; D014503:Urate Oxidase / Q000235:genetics
D002352:Carrier Proteins; D006021:Glycophorins; C491242:Lgals9 protein, rat; D027361:Organic Anion Transporters; D027701:Organic Cation Transport Proteins; C491241:SLC22A12 protein, human; C103862:urate transporter; D011718:Pyrazinamide; C005296:pyrazinoic acid; D010094:Oxonic Acid; D012266:Ribose; D014503:Urate Oxidase; D005947:Glucose; D007785:Lactose; D000241:Adenosine