The L. monocytogenes protein InIB activates phosphoinositide 3-kinase and induces phagocytosis in several mammalian cell types. The 1.86 Å resolution X-ray crystal structure of the leucine-rich repeat domain of InIB that is both necessary and sufficient to induce phagocytosis is presented here. The structure supports a crucial role for calcium in host cell invasion by L. monocytogenes and supplies a rationale for its function. Calciums are bound to the protein in an unusually exposed manner that suggests that the metals may act as a bridge between InIB and mammalian cell surface receptors. The structure also identifies surfaces on the curved and elongated molecule that may constitute additional interaction sites in forming a bacterial-mammalian signaling complex.
Marino, M., Braun, L., Cossart, P., & Ghosh, P. (1999). Structure of the InIB leucine-rich repeats, a domain that triggers host cell invasion by the bacterial pathogen L. monocytogenes. Molecular Cell, 4(6), 1063–1072. https://doi.org/10.1016/S1097-2765(00)80234-8