Required for invasion of epithelial cells, as well as for survival within host cells, escape from endocytic vesicles and subsequent actin-tail formation. Probably regulates the secretion of effectors BipB and BipC and their final integration into the target cell membrane (By similarity). Secreted via the bsa type III secretion system. Localizes to the tip of the external secretion needle that is part of the secretion apparatus (By similarity). The N-terminal domain is an intra-molecular chaperone that prevents premature oligomerization of the residues on the coiled-coil region that are involved in interactions with the needle and/or itself. The residues in the C-terminal domain probably form oligomeric structures at the tip of the needle that are responsible for the regulation of secretion of other effectors (By similarity). Belongs to the invasin protein D family.