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Am J Physiol Renal Physiol (February 20, 2002). doi:10.1152/ajprenal.00333.2001
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Articles in PresS, published online ahead of print February 19, 2002
Am J Physiol Renal Physiol, 10.1152/ajprenal.00333.2001
Submitted on November 1, 2001
Accepted on February 12, 2002

Functional analysis and molecular model of the human urate transporter/channel, hUAT

Edgar Leal-Pinto1, B. Eleazar Cohen2, Michael S Lipkowitz1, and Ruth G Abramson1*

1 Division of Nephrology, Department of Medicine, Mount Sinai School of Medicine, New York, New York, USA
2 Division of Extramural Activities, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, USA

* To whom correspondence should be addressed. E-mail: raBRAMSON{at}smtplink.mssm.EDU.

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 ß 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.




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