Structure and Mechanism of the Glycerol-3-Phosphate Transporter from <i>Escherichia coli</i>

TLDR

The major facilitator superfamily is the largest group of secondary membrane transporters in the cell. The authors propose that GlpT operates via a single‑binding site alternating‑access mechanism. This mechanism involves a rocker‑switch type movement that shifts the protein between inward‑ and outward‑facing conformations. The 3.3 Å crystal structure shows GlpT’s pseudo two‑fold symmetry, a central pore with two arginine residues as the binding site, and a compact conformation induced by substrate binding, illustrating its glycerol‑3‑phosphate and inorganic phosphate transport functions.

Abstract

The major facilitator superfamily represents the largest group of secondary membrane transporters in the cell. Here we report the 3.3 angstrom resolution structure of a member of this superfamily, GlpT, which transports glycerol-3-phosphate into the cytoplasm and inorganic phosphate into the periplasm. The amino- and carboxyl-terminal halves of the protein exhibit a pseudo two-fold symmetry. Closed off to the periplasm, a centrally located substrate-translocation pore contains two arginines at its closed end, which comprise the substrate-binding site. Upon substrate binding, the protein adopts a more compact conformation. We propose that GlpT operates by a single–binding site, alternating-access mechanism through a rocker-switch type of movement.