게시판

Principal Investigator
- Myung Hee Kim, Infection and Immunity Research Center / July 2013

R&D Background
- Pathogenic bacteria that colonize the host gut are exposed to an adverse environment and competitors. These bacteria overcome the limited availability of nutrients in the gut by using alternative carbon sources. The mammalian intestinal tract is protected by a mucus layer, which contains heavily glycosylated mucin proteins that comprise up to 85% carbohydrate. Sialic acids, which can be used as an energy source by a variety of microbial pathogens and commensals, are found at the distal ends of the mucin carbohydrate chains. Because the most abundant sialic acid is N-acetylneuraminic acid (Neu5Ac), intestinal commensal and pathogenic bacteria have most likely evolved elaborate systems for the catabolic utilization of this substrate. The correct function of the associated catabolic machinery is particularly crucial for the pathogenesis of enteropathogenic bacteria during infection, although the molecular mechanisms involved with the regulation of the catabolic machinery are unknown.

Research Summary
- We determined the complex structure of NanR, a repressor of the nan genes responsible for Neu5Ac catabolism, and its regulatory ligand, ManNAc-6P, in the human pathogenic bacterium Vibrio vulnificus. Structural studies combined with electron microscopic, biochemical, and in vivo analysis demonstrated that NanR forms a dimer in which the two monomers create an arched tunnel-like DNA-binding space, which contains positively charged residues that interact with the nan promoter. The interaction between the NanR dimer and DNA is alleviated by the ManNAc-6P?mediated relocation of residues in the ligand-binding domain of NanR, which subsequently relieves the repressive effect of NanR and induces the transcription of the nan genes. Survival studies in which mice were challenged with a ManNAc-6P?binding-defective mutant strain of V. vulnificus demonstrated that this relocation of NanR residues is critical for V. vulnificus pathogenesis.
Applied Cases and Effects
- The catabolic utilization of Neu5Ac is important for bacterial pathogenesis, so molecules that target NanR may have several advantages over conventional antibiotics as unique antimicrobial reagents. First, such molecules could reduce the growth rate of invading pathogens, which would help the immune system to eliminate pathogens from the host. Second, the use of antagonists to block the binding of ManNAc-6P to NanR is unlikely to disturb the normal flora of the host because the mechanisms that regulate the nan genes in typical commensal bacteria differ from those in V. vulnificus. Therefore, our results provide a starting point for the design of antibiotics to target life-threatening Vibrio species.




Principal Investigator Myung Hee Kim, Infection and Immunity Research Center / July 2013 R&D Background Pathogenic bacteria that colonize the host gut are exposed to an adverse environment and competitors. These bacteria overcome the limited availability of nutrients in the gut by using alternative carbon sources. The mammalian intestinal tract is protected by a mucus layer, which contains heavily glycosylated mucin proteins that comprise up to 85% carbohydrate. Sialic acids, which can be used as an energy source by a variety of microbial pathogens and commensals, are found at the distal ends of the mucin carbohydrate chains. Because the most abundant sialic acid is N-acetylneuraminic acid (Neu5Ac), intestinal commensal and pathogenic bacteria have most likely evolved elaborate systems for the catabolic utilization of this substrate. The correct function of the associated catabolic machinery is particularly crucial for the pathogenesis of enteropathogenic bacteria during infection, although the molecular mechanisms involved with the regulation of the catabolic machinery are unknown. Research Summary We determined the complex structure of NanR, a repressor of the nan genes responsible for Neu5Ac catabolism, and its regulatory ligand, ManNAc-6P, in the human pathogenic bacterium Vibrio vulnificus. Structural studies combined with electron microscopic, biochemical, and in vivo analysis demonstrated that NanR forms a dimer in which the two monomers create an arched tunnel-like DNA-binding space, which contains positively charged residues that interact with the nan promoter. The interaction between the NanR dimer and DNA is alleviated by the ManNAc-6P?mediated relocation of residues in the ligand-binding domain of NanR, which subsequently relieves the repressive effect of NanR and induces the transcription of the nan genes. Survival studies in which mice were challenged with a ManNAc-6P?binding-defective mutant strain of V. vulnificus demonstrated that this relocation of NanR residues is critical for V. vulnificus pathogenesis. Applied Cases and Effects The catabolic utilization of Neu5Ac is important for bacterial pathogenesis, so molecules that target NanR may have several advantages over conventional antibiotics as unique antimicrobial reagents. First, such molecules could reduce the growth rate of invading pathogens, which would help the immune system to eliminate pathogens from the host. Second, the use of antagonists to block the binding of ManNAc-6P to NanR is unlikely to disturb the normal flora of the host because the mechanisms that regulate the nan genes in typical commensal bacteria differ from those in V. vulnificus. Therefore, our results provide a starting point for the design of antibiotics to target life-threatening Vibrio species.