Molecular Dynamics Studies Support Elevator Type Transport Mechanisms in the Glucose EIIC Superfamily Transporters

Abstract

The phosphoenolpyruvate-dependent phosphotransferase system (PTS) provides a distinct sugar transportation pathway in bacteria. Because PTS does not exist in eukaryotes, it is considered a novel target for antibiotics development. Among the components of PTS, the enzyme IIC (EIIC), a membrane transporter protein, is particularly important since it transports a sugar through the bacterial cell membrane. In 2011, Cao et al. first determined the crystal structure of chitobiose-specific EIIC (bcChbC) in an inward-facing occluded state. In addition, we have recently determined the crystal structure of maltose-specific EIIC (bcMalT) in an outward-facing occluded state. The crystal structures suggest an “Elevator” type transportation mechanism, but the accurate mechanism of how EIIC transports a sugar has not been clearly demonstrated yet. To investigate more detailed and accurate transportation mechanisms, we performed collective variable-based steered molecular dynamics (CVSMD) simulations. Our simulation shows the spontaneous transportation of the sugar toward the opposite side of the membrane with the preserved H-bonding interactions, supporting the “Elevator” type transport mechanism. A set of cross-linking experiments was carried out on the basis of the CVSMD model structures, and we were able to acquire a few of stable cross-linked structures.