Required for translocation of effector proteins via the type III secretion system SPI-1, which is essential for an efficient bacterial internalization. Probably acts by modulating the secretion of SipA, SipB, and SipC. Secreted via the type III secretion system 1 (SPI-1 TTSS). Transcriptionally regulated by SicA and InvF. Also regulated by InvE. 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.