Involved in the triggering of intracellular events that lead to microbial internalization. These events include increase in calcium level, redistribution of actin microfilaments, and changes in the normal structure of the microvilli. Encoded within the type III secretion system (SPI-1 TTSS), it is essential for the translocation of protein effectors into host cells. Forms a complex with SipB and SipC in the presence of their chaperone SicA. Positively regulates the secretion of SPI-1 TTSS effector proteins SipB, SipC and SipD and negatively influences the secretion of SipA, SopA and SptP. Probably associated with a bacterial membrane-localized protein.