Acts as a negative regulator of the type III secretion regulon (T3SS) expression (PubMed:15911752). In the absence of inducing signals such as low Ca(2+) or host cell contact, the T3SS/injectisome is expressed at a low basal level and exists in a quiescent state due to ExsA sequestration by ExsD. ExsE binding to ExsC disrupts the complex between ExsC and ExsD, thereby allowing free ExsD to bind ExsA (PubMed:15911752, PubMed:15985546). Upon inducing signal, ExsE is secreted allowing ExsC to bind ExsD. In turn, ExsD cannot bind ExsA and prevent ExsA-mediated transcriptional activation of the type III secretion system (PubMed:15911752, PubMed:15985546). Interacts with ExsC. Secreted under low-calcium conditions. Deletion mutant deregulates expression of the type III secretion genes.