CesAB is an enteropathogenic Escherichia coli chaperone for the type-III translocator proteins EspA and EspB

Abstract

Enteropathogenic Escherichia coli (EPEC) are extracellular pathogens that colonize mucosal surfaces of the intestine via formation of attaching and effacing (A/E) lesions. The genes responsible for induction of the A/E lesions are located on a pathogenicity island, termed the locus of enterocyte effacement (LEE), which encodes the adhesin intimin and the type III secretion system needle complex, translocator and effector proteins. One of the major EPEC translocator proteins, EspA, forms a filamentous conduit along which secreted proteins travel before they arrive at the translocation pore in the plasma membrane of the host cell, which is composed of EspB and EspD. Prior to secretion, many type III proteins, including translocators, are maintained in the bacterial cytoplasm by association with a specific chaperone. In EPEC, chaperones have been identified for the effector proteins Tir, Map and EspF, and the translocator proteins EspD and EspB. In this study, CesAB (Orf3 of the LEE) was identified as a chaperone for EspA and EspB. Specific CesAB–EspA and CesAB–EspB protein interactions are demonstrated. CesAB was essential for stability of EspA within the bacterial cell prior to secretion. Furthermore, a cesAB mutant failed to secrete EspA, as well as EspB, to assemble EspA filaments, to induce A/E lesion following infection of HEp-2 cells and to adhere to, or cause haemolysis of, erythrocytes.

Identification of a Third EspA-binding Protein That Forms Part of the Type III Secretion System of Enterohemorrhagic Escherichia coli

“…Secretion of the TTS translocators requires the assistance of cytoplasmic chaperones that have some common properties, namely that they have a low molecular mass (Ͻ15 kDa), have an acidic pI, and contain a C-terminal amphipathic helix (41). Up to now two chaperones (CesAB and CesA2) are reported to act with EspA (20,29,40), two (CesD and CesD2) with EspD (7,31,42), and one (CesAB) with EspB (29,40). CesD, CesD2, CesAB, and CesA2 all have chaperone properties as described above except that CesAB has a basic pI.…”

“…Analysis of EspA Stability-The method of measuring EspA stability has previously been reported (29). An EHEC strain harboring pEspA was cultured in M9 for 4.5 h, then 1 mM isopropyl 1-thio-␤-D-galactopyranoside was added to induce EspA production.…”

A genomic population genetics analysis of the pathogenic enterocyte effacement island in Escherichia coli : The search for the unit of selection

“…The adhesin receptor tir is transferred into host cells, where it is modified by host kinases, and becomes inserted into the plasma membrane to orchestrate cytoskeletal rearrangements; this activity depends on its interaction with the adhesin (eae) and tyrosine phosphorylation (18). The secreted proteins are required for the translocation of other proteins into the host cell; in the specific case of espA, this protein forms a filamentous conduit along which secreted proteins travel before they arrive at the translocation pore in the plasma membrane of the host cell, comprised of espB and espD (19,20). Many secreted proteins before secretion are maintained in the bacterial cytoplasm by association with a specific chaperone (19)(20)(21).…”

“…The secreted proteins are required for the translocation of other proteins into the host cell; in the specific case of espA, this protein forms a filamentous conduit along which secreted proteins travel before they arrive at the translocation pore in the plasma membrane of the host cell, comprised of espB and espD (19,20). Many secreted proteins before secretion are maintained in the bacterial cytoplasm by association with a specific chaperone (19)(20)(21). The 41 genes are organized in five polycystronic operons known as LEE1, LEE2, LEE3, TIR, and LEE4, all of them positively regulated by ler (12), which is localized at LEE1.…”

“…The average size of LEE is Ϸ35 kb with a GC content of 38% (14,15), which is very different from the housekeeping genes of E. coli (GC content ϭ 50%) (4). The locus comprises 41 genes that include a type III secretion system (TTSS) (16), an adhesin-denominated intimin (eae) (17), its receptor (tir) (18), several secreted proteins (espA, espD, espB, and espF), and their chaperones (19). The TTSS apparatus directs the transfer of specific proteins across the bacterial envelope, where the secreted proteins function to transfer effector proteins into host cells (16).…”