Characterization of a novel Escherichia coli exopolysaccharide and its biosynthesis by NfrB

Abstract

Biofilms are made from an association of bacterial cells and extracellular products dominated by a plethora of exopolysaccharides. Accumulating evidence have demonstrated that the bacterial second messenger cyclic-di-guanosine monophosphate (c-di-GMP) promotes the synthesis of these exopolysaccharides through direct allosteric activation of glycosyltransferase enzymes. The Escherichia coli inner membrane protein NfrB, which together with the outer membrane protein NfrA acts as a receptor system for phage N4, contains a N-terminal glycosyltransferase domain and C-terminal c-di-GMP binding domain. Recent research revealed that NfrB is a novel, c-di- GMP controlled glycosyltransferase that is proposed to synthesize a N-acetylmannosamine containing polysaccharide product, though the exact structure and function of this remains unknown. Nfr polysaccharide production impedes bacterial motility, which suggests a possible role of the Nfr proteins in bacterial biofilm formation. Here, we carry out in-vivo synthesis of novelNfr polysaccharide followed by its structural characterization. Preliminary data from MALDI- TOF mass spectrometry and Solid State 13C NMR spectroscopy indicated that the Nfr polysaccharide is mainly a homo polymer of poly-?-(1®4)-N-acetylmannosamine, bound to an aglycone. In addition, we report efforts to develop of a Nfr polysaccharide binding and detection tool, through the mutation of YbcH, a putative Nfr polysaccharide hydrolase enzyme. These studies advance the understanding of Nfr polysaccharide biosynthesis and could offer potential new targets for the development of antibiofilm and antibacterial therapies.