Crystal structure and mechanism of GlpT, the glycerol-3-phosphate transporter from E. coli.
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 A 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.
Lemieux
M Joanne
MJ
Skirball Institute for Biomolecular Medicine, New York University School of Medicine, 540 First Ave., 3-5, New York, NY 10016, USA. mlemieux@ualberta.ca
Huang
Yafei
Y
Wang
Da Neng
da N
D003460:Crystallization; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D021381:Protein Transport; D013329:Structure-Activity Relationship
D029968:Escherichia coli Proteins; C488962:GlpT protein, E coli; D026901:Membrane Transport Proteins