Elucidating the Self-assembly of Lactobacilli surface-Layer Proteins

Surface layers (S-layers) are protein coats displayed on the external surface of many bacterial and archaeal species. They are unique between different species. In pathogenic bacteria, S- layers contribute to virulence as they provide a large surface area for interaction with host cells which implies tremendous implications for the immune response and human disease. Nevertheless, the underlying mechanisms of S-layers are poorly understood, primarily due to lack of structural knowledge. The tendency of wild-type S-layer proteins to form two- dimensional-crystalline lattices makes it very difficult to produce three-dimensional-crystals, which are the prerequisite for crystallographic structure determination. In this project, we focus on the structural and functional characterization of S-layer proteins and their domains from lactobacilli. Lactobacilli belong to the generally recognized as safe (GRAS) microorganism and represent health-promoting factors to their host. As the outermost layer in different species of lactobacilli, the S-layers are in direct contact with the bacterial environment and thus involved in many of their surface properties, e.g. adhesion to epithelial cells and to intestinal components. Therefore, the structural investigation of surface properties of lactobacilli possessing S-layers will provide the basis for understanding both, the mechanism involved in adhesion properties and the biological functions of the S-layer. Novel in our current approach is the structure determination of distinct domains of the S-layer protein in combination with different complimentary methods, such as nuclear magnetic resonance spectroscopy, mass spectrometry, electron microscopy and biochemical methods. Consequently, the outcome of these studies will have a prominent impact on our ability to exploit S-layer proteins, including the development of novel components for vaccines against infectious diseases.