This family represents a chaperone protein for the type III secretion system - TTSS - translocon protein EspA, to prevent the latter's self-polymerisation. The TTSS is a highly specialised bacterial protein secretory pathway, similar in many ways to the flagellar system, that is essential for the pathogenesis of many Gram-negative bacteria. The twenty or so proteins making up the TTSS apparatus, referred to as the needle complex, allow the injection of virulence proteins (known as effectors) directly into the cytoplasm of the eukaryotic host cells they infect; however, the injection process itself is mediated by a subset of extracellular proteins that are secreted by the needle complex to the bacterial surface and assembled into the type III translocon - EspA. EspB and EspD. EspA polymerises into an extracellular filament, and, as with other fibrous proteins, is apt to undergo massive polymerisation when overexpressed. CesA is the secretion chaperone protein that binds to EspA. CesA is dimeric and helical, and it traps EspA in a monomeric state and inhibits its polymerisation.

1: Structural characterization of a type III secretion system filament protein in complex with its chaperone. Yip CK, Finlay BB, Strynadka NC; Nat Struct Mol Biol. 2005;12:75-81. PMID:15619638