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Journal of Electron Microscopy 2005 54(supplement 1):i43-i46; doi:10.1093/jmicro/54.suppl_1.i43
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© The Author 2005. Published by Oxford University Press on behalf of Japanese Society of Microscopy. All rights reserved. For permissions, please email: journals.permissions@oupjournals.org

Article

Crystal structure and mechanism of GlpT, the glycerol-3-phosphate transporter from E. coli

M. Joanne Lemieux1,2,*, Yafei Huang1 and Da Neng Wang1

1 Skirball Institute for Biomolecular Medicine, New York University School of Medicine, 540 First Ave., 3-5, New York, NY 10016, USA

* To whom correspondence should be addressed. E-mail: mlemieux{at}ualberta.ca

Abstract

The major facilitator superfamily represents the largest group of secondary active membrane transporters in prokaryotic and eukaryotic cells. They transport a vast variety of substrates, presumably via similar mechanisms, yet the details of these mechanisms remain unclear. Here we report the 3.3 Å resolution structure of a member of this superfamily—GlpT, the glycerol-3-phosphate transporter from the E. coli inner membrane, in the absence of a substrate. The antiporter mediates the exchange of glycerol-3-phosphate for inorganic phosphate across the membrane. Its N- and C-terminal domains exhibit a pseudo 2-fold symmetry along an axis perpendicular to the membrane. Eight of the twelve transmembrane {alpha}-helices are arranged around a centrally located substrate translocation pore that is closed off at the periplasmic surface. Present at the beginning of the pore are two arginine residues that presumably comprise the substrate-binding site which is accessible only from the cytosol, suggesting an inward-facing conformation for the transporter. The central loop connecting the N- and C-terminal domains is partially disordered and exhibits reduced susceptibility to trypsin in the presence of substrate, indicating conformational changes. We propose that GlpT operates via a single binding-site, alternating-access mechanism.

Keywords     GlpT, transporter, membrane protein, crystallization, MFS

Received      1 March 2004, accepted 15 October 2004


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