is a Gram-negative, facultative anaerobic bacterial species that causes serious disease and can grow on various carbon sources, including chitin polysaccharides. In saltwater, its attachment to chitin surfaces not only serves as the initial step of nutrient recruitment but is also a crucial mechanism underlying cholera epidemics. In this study, we report the first characterization of a chitooligosaccharide-specific chitoporin, ChiP, from the cell envelope of the type strain O1. We modeled the structure of ChiP, revealing a trimeric cylinder that forms single channels in phospholipid bilayers. The membrane-reconstituted ChiP channel was highly dynamic and voltage induced. Substate openings O', O', and O', betwe... More
is a Gram-negative, facultative anaerobic bacterial species that causes serious disease and can grow on various carbon sources, including chitin polysaccharides. In saltwater, its attachment to chitin surfaces not only serves as the initial step of nutrient recruitment but is also a crucial mechanism underlying cholera epidemics. In this study, we report the first characterization of a chitooligosaccharide-specific chitoporin, ChiP, from the cell envelope of the type strain O1. We modeled the structure of ChiP, revealing a trimeric cylinder that forms single channels in phospholipid bilayers. The membrane-reconstituted ChiP channel was highly dynamic and voltage induced. Substate openings O', O', and O', between the fully open states O, O, and O, were polarity selective, with nonohmic conductance profiles. Results of liposome-swelling assays suggested that ChiP can transport monosaccharides, as well as chitooligosaccharides, but not other oligosaccharides. Of note, an outer-membrane porin (omp)-deficient strain of expressing heterologous ChiP could grow on M9 minimal medium supplemented with small chitooligosaccharides. These results support a crucial role of chitoporin in the adaptive survival of bacteria on chitinous nutrients. Our findings also suggest a promising means of vaccine development based on surface-exposed outer-membrane proteins and the design of novel anticholera agents based on chitooligosaccharide-mimicking analogs.
