GlpT

GlpT is a membrane transporter found in the inner membrane of many Gram-negative bacteria, most notably Escherichia coli. It is the glycerol-3-phosphate transporter, encoded by the glpT gene, and plays a key role in importing glycerol-3-phosphate from the environment for metabolism.

GlpT functions as a secondary active transporter that operates as an antiporter for glycerol-3-phosphate and inorganic phosphate. In typical operation, glycerol-3-phosphate from outside the cell is imported in exchange for inorganic phosphate moving in the opposite direction. The transport process is driven by the electrochemical gradients across the inner membrane and occurs through alternating access of the substrate-binding site, a hallmark of many major facilitator superfamily transporters. GlpT is predicted to contain about 12 transmembrane helices, a common architecture among MFS transporters.

Physiologically, GlpT enables bacteria to utilize glycerol-3-phosphate as a carbon and energy source. Imported glycerol-3-phosphate can be oxidized by glycerol-3-phosphate dehydrogenase (GlpD) to dihydroxyacetone phosphate, which feeds into glycolysis. This pathway supports growth when glycerol-3-phosphate is available in the environment and links to broader carbon metabolism.

Genetically, glpT is part of the glp regulon, often co-regulated with glpD. Expression of glpT can be influenced by global regulatory networks that respond to carbon source availability, such as Crp-cAMP in enteric bacteria, aligning transporter production with metabolic needs.

Research on GlpT has contributed to understanding the mechanisms of MFS antiporters and substrate exchange. While detailed high-resolution structures are less common than for some other transporters, GlpT remains a reference point for studying glycerol-3-phosphate metabolism and inner-m membrane transport in bacteria.