inlB

InlB, or internalin B, is a surface-associated protein produced by the bacterium Listeria monocytogenes. It belongs to the internalin family of virulence factors and plays a key role in promoting the invasion of non-phagocytic host cells, thereby contributing to the organism’s pathogenic spread.

InlB is encoded by the inlB gene and is anchored to the bacterial cell wall via a C-terminal LPXTG motif, requiring the sortase A enzyme for covalent attachment. The protein is exported through the Sec secretion pathway and is presented on the bacterial surface, where its domains mediate interactions with host cells.

The primary mechanism attributed to InlB is binding to the Met receptor (the hepatocyte growth factor receptor) on the surface of host cells. This interaction activates Met signaling and downstream pathways that rearrange the actin cytoskeleton, facilitating bacterial internalization. InlB’s activity can enable Listeria to invade a broader range of cell types, including hepatocytes and endothelial cells, contributing to dissemination during infection. The effectiveness of invasion can vary with host cell type and is modulated by regulatory factors such as PrfA, the master virulence regulator, which controls expression of InlB in response to environmental cues.

InlB functions alongside other virulence factors such as InlA to orchestrate multi-step invasion processes, including crossing the intestinal barrier and subsequent systemic spread. In research settings, InlB is used to study receptor-mediated endocytosis and host–pathogen interactions, and engineered forms have been explored as tools to investigate delivery of cargo into cells.

Overall, InlB is a key virulence determinant that expands Listeria monocytogenes’ ability to invade host cells by engaging the Met receptor and initiating internalization signaling.