Involved in a secretory pathway responsible for the surface presentation of determinants needed for the entry of Salmonella species into mammalian cells. Chaperone specialized in the storage of effectors within the bacterial cytoplasm, maintaining them in a secretion-competent state, and allowing their immediate delivery to target cells upon contact of the bacterium with the host cells. Has been shown to chaperone SopA, SopE, SopE2 and SipA. Homodimer. Belongs to the SpaK family.