Single-channel characterization of the chitooligosaccharide transporter chitoporin (SmChiP) from the opportunistic pathogen Serratia marcescens

Serratia marcescens is an opportunistic pathogen that can utilize chitin as a carbon source, through its ability to produce chitin-degrading enzymes to digest chitin and membrane transporters to transport the degradation products (chitooli-gosaccharides) into the cells. Further characterization of these proteins is important to understand details of chitin meta-bolism. Here, we investigate the properties and function of the S. marcescens chitoporin, namely SmChiP, a chitooligo-saccharide transporter. We show that SmChiP is a monomeric porin that forms a stable channel in artificial phospholipid membranes, with an average single-channel conductance of 0.5 +/- 0.02 nS in 1 M KCl electrolyte. Additionally, we demonstrated that SmChiP allowed the passage of small mol-ecules with a size exclusion limit of <300 Da and exhibited substrate specificity toward chitooligosaccharides, both in membrane and detergent-solubilized forms. We found that SmChiP interacted strongly with chitopentaose (Kd = 23 +/- 2.0 mu M) and chitohexaose (Kd = 17 +/- 0.6 mu M) but did not recognize nonchitose oligosaccharides (maltohexaose and cel-lohexaose). Given that S. marcescens can use chitin as a primary energy source, SmChiP may serve as a target for further development of nutrient-based antimicrobial therapies directed against multidrug antibiotic-resistant S. marcescens infections.

Automated summary

Serratia marcescens is an opportunistic pathogen that can utilize chitin as a carbon source. It produces chitin-degrading enzymes and membrane transporters to digest and transport chitin degradation products. In this study, the properties and function of the chitooligosaccharide transporter, SmChiP, were investigated. SmChiP is a monomeric porin that forms a stable channel and exhibits substrate specificity towards chitooligosaccharides. It may serve as a target for the development of antimicrobial therapies against multidrug antibiotic-resistant S. marcescens infections.