中国科学院昆明动物研究所机构知识库

The phosphoenolpyruvate-dependent phosphotransferase system(PTS) transports sugar into bacteria and phosphorylates the sugarfor metabolic consumption. The PTS is important for the survival ofbacteria and thus a potential target for antibiotics, but itsmechanism of sugar uptake and phosphorylation remains unclear.The PTS is composed of multiple proteins, and the membrane-embedded Enzyme IIC (EIIC) component transports sugars acrossthe membrane. Crystal structures of two members of the glucosesuperfamily of EIICs, bcChbC and bcMalT, were solved in the inward-facing and outward-facing conformations, and the structures sug-gest that sugar translocation could be achieved by movement ofa structured domain that contains the sugar-binding site. How-ever, different conformations have not been captured on thesame transporter to allow precise description of the conforma-tional changes. Here we present a crystal structure of bcMalT trap-ped in an inward-facing conformation by a mercury ion thatbridges two strategically placed cysteine residues. The structureallows direct comparison of the outward- and inward-facing con-formations and reveals a large rigid-body motion of the sugar-binding domain and other conformational changes that accompanythe rigid-body motion. All-atom molecular dynamics simulationsshow that the inward-facing structure is stable with or withoutthe cross-linking. The conformational changes were further val-idated by single-molecule Föster resonance energy transfer(smFRET). Combined, these results establish the elevator-typemechanism of transport in the glucose superfamily of EIICtransporters.