The three known transport modes of GlpT, depending on the availability of Glycerol-3-phosphate (G3P) and P i . GlpT’s G3P and P i antiport is bi-directional, in a concentration-dependent manner. In the first hypothetical scenario, there is more G3P than P i in the periplasm and the main transport direction in G3P import and P i export, by equimolar G3P:P i antiport. In the second hypothetical scenario, there is more Pi than G3P in the periplasm, and the main transport direction is P i import and G3P export, by equimolar P i :G3P antiport. GlpT can additionally import P i by non-equimolar exchange of 2P i :1P i in E. coli , which is shown in the third scenario. The different numbers of representative P i and G3P molecules aim at representing different periplasmic/cytoplasmic concentrations. Created in BioRender. Santamaria de Souza (2025) https://BioRender.com/d47n170
