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Biophys. J. BioFAST: First Published August 31, 2004. doi:10.1529/biophysj.104.049320
© 2004 by the Biophysical Society.

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BIOENERGETICS

Structure and transport mechanism of the bacterial oxalate transporter OxlT

Teruhisa Hirai 1 and Sriram Subramaniam 1*

1 NCI

* To whom correspondence should be addressed. E-mail: ss1{at}nih.gov.

Submitted on July 8, 2004
Revised on August 4, 2004
Accepted on 20 August 2004


  Abstract
Membrane proteins that belong to the Major Facilitator Superfamily (MFS) are found in organisms across the evolutionary spectrum and mediate the transport of a variety of substrates ranging from small metabolites to neurotransmitters. The oxalate transporter (OxlT) is a representative MFS protein, and exchanges formate for oxalate across the cytoplasmic membrane of the organism Oxalobacter formigenes. Here, we present a structural model for the protein conformational changes that occur during oxalate transport by combining a three-dimensional map of the oxalate-bound, "closed" state of OxlT at 6.5 Å; determined by cryo-electron microscopy with a model of the "open" state of OxlT based on the atomic structures of the related transporters Glycerol-3-phosphate transporter (GlpT) and Lactose permease (LacY). We demonstrate that the principal structural change associated with substrate transport is a concerted rocking movement of the two structurally similar halves of the protein relative to each other. Our structural model places two positively charged residues, Arg 272 and Lys 355 in the central cavity, suggesting that electrostatic interactions between these residues and the oxalate anion is a key step in generating the conformational change between the open and closed states of the transporter.

Key Words: conformational change, electron microscopy, membrane protein, secondary transporter




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Copyright © 2004 by the Biophysical Society.