Resolving atomic site interactions of the Y. pestis outer membrane protein Ail with human serum in the bacterial cell envelope

Abstract

Understanding microbe-host interactions at the molecular level is a major goal of fundamental biology and therapeutic drug development. Structural biology strives to capture biomolecular structures in action, but the samples are often highly simplified versions of the complex native environment. Here we present an E. coli model system that allows us to probe the structure and function of Ail, the major surface protein of the deadly pathogen Yersinia pestis. We show that cell surface expression of Ail produces Y. pestis virulence phenotypes in E. coli, including resistance to human serum, co-sedimentation of human vitronectin and pellicle formation. Moreover, isolated bacterial cell envelopes, encompassing inner and outer membranes, yield high-resolution solid-state nuclear magnetic resonance (NMR) spectra that reflect the structure of Ail and reveal Ail sites that are sensitive to the bacterial membrane environment and involved in the interactions with human serum components. The data capture the structure and function of Ail in a bacterial outer membrane and set the stage for probing its interactions with the complex milieu of immune response proteins present in human serum. SIGNIFICANCEAil is a critical virulence factor of Y. pestis, and its interactions with human serum are central for promoting the immune resistance of bacteria to the human host defenses. Here we capture the action of Ail in a functional bacterial environment and set the stage for probing its interactions with the complex milieu of immune response proteins present in human serum. The development of an E. coli model system of Y. pestis for biophysical studies is new and biologically important. Finally, the work extends the range in-situ NMR spectroscopy to include models of microbial infection.