Structural insight into Vibrio cholerae EIIC sugar transporter dimer captured in a substrate-free inward-facing state

The phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) is a central pathway for carbohydrate transport in bacteria and plays a critical role in nutrient acquisition, metabolism, and virulence. In Vibrio cholerae, the glucose-specific EIIC transporter is a key component of the PTS system, mediating the transport of sugars into the bacterial cell, coupled with phosphorylation during translocation. Here, we present the 3.68 Å cryo-electron microscopy (cryo-EM) structure of the dimeric EIIC transporter from Vibrio cholerae in its inward-facing, substrate-free conformation. The structure reveals a detailed arrangement of the scaffold and transport domains, stabilized by extensive inter- and intraprotomer interactions. Comparative analysis with substrate-bound inward-facing structures of EIIC from E. coli highlights conformational changes, providing insights into substrate release and the structural transitions required for alternating access. Notably, the observed substrate-free inward-facing conformation features a larger substrate-binding pocket, which is consistent with a state poised for glucose release into the cytoplasm. The formation of a unique intraprotomer disulfide bond between residues C240 and C254 stabilizes the interface between the scaffold and transport domains, potentially regulating transporter dynamics. These findings elucidate the structural basis for substrate release in the PTS system and underscore the dynamic nature of EIIC-mediated sugar transport. Our study enhances the understanding of PTS system function in Vibrio cholerae and highlights the EIIC transporter as a promising target for antimicrobial drug development. Disruption of sugar transport in this essential pathway could impair bacterial growth and virulence, suggesting a novel therapeutic strategy against cholera. These results provide a foundation for future investigations into the structural and functional dynamics of bacterial sugar transporters.