Molecular mechanisms of type III secretion effector NleL in enterohemorrhagic Escherichia coli O157:H7 pathogenesis
Abstract
EHEC, a member of the attaching and effacing (A/E) pathogen group of bacteria, causes hemorrhagic colitis and may result in potentially fatal hemolytic uremia syndrome. Effective infection of host intestinal epithelial cells by EHEC is a result of coordinated interactions of bacterial effectors and/or host cellular proteins. Several key effectors involved in the process of infection have been identified yet certain aspects of the pathogenicity of EHEC remain unclear. While we understand much of the molecular dynamics of cytoskeletal rearrangements, we still lack comprehensive knowledge of all bacterial effectors involved in pedestal formation. Therefore, identification and functional characterization of novel effectors is important for understanding the mechanism of pedestal formation during EHEC infection and A/E pathogenesis in general. We report discovery of a novel effector protein called Non-LEE encoding Ligase (NleL) encoded by the ECs1560 locus of EHEC. In vitro, we show that NleL translocates into the host cell via the TTSS and is an E3 ubiquitin ligase with the C753 residue being critical for its activity. While E3 ubiquitin ligases have been reported from intracellular animal pathogens like Salmonella and Shigella, NleL is the first E3 ubiquitin ligase identified from an extracellular animal pathogen. Functionally, we show that not only is NleL required but it is its E3 ubiquitin ligase activity that is essential for pedestal formation under conditions of sub optimal expression of TTSS effectors. Furthermore, we report that NleL specifically interacts with another EHEC effector Tir and a host cell derived E3 ubiquitin ligase HsRma1. However, the exact nature and role of these interactions still remains unclear. More significantly, we have discovered a homolog of NleL from Citrobacter rodentium. We show that NleLc is a bona fide E3 ubiquitin ligase and that function of NleLc is required to carry out efficient infection of murine colonic epithelial cells In vivo. Ongoing research focuses on characterization of molecular interactions of NleL with Tir and HsRma1 and identification of other putative binding partners of NleL.
Degree
Ph.D.
Advisors
Zhou, Purdue University.
Subject Area
Microbiology
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