The coiled-coil domain of EspA is essential for the assembly of the type III secretion translocon on the surface of enteropathogenic Escherichia coli

Enteropathogenic E. coli (EPEC) utilize a type III secretion system to deli ver virulence-associated effector proteins to the host cell. Four proteins, EspA, EspE, EspD, and Tir, which are integral to the formation of characte ristic "attaching and effacing" (A/E) intestinal lesions, are known to be e xported via the EPEC type III secretion system. Recent work demonstrated th at EspA is a major component of a filamentous structure, elaborated on the surface of EPEC, which is required for translocation of EspB and Tir, The c arboxyl terminus of EspA is predicted to comprise an alpha-helical region, which demonstrates heptad periodicity whereby positions a and d in the hept ad repeat unit abcdefg are occupied by hydrophobic residues, indicating a p ropensity for coiled-coil interactions. Here we demonstrate multimeric EspA isoforms in EPEC culture supernatants and EspA:EspA interaction on solid p hase. Non-conservative amino acid substitution of specific EspA heptad resi dues generated EPEC mutants defective in filament assembly but which retain ed the ability to induce A/E lesions; additional mutation totally abolished EspA filament assembly and A/E lesion formation. These results demonstrate a similarity to flagellar biosynthesis and indicate that the coiled-coil d omain of EspA is required for assembly of the EspA filament-associated type III secretion translocon.