Untagged Selleckchem Androgen Receptor Antagonist cis-complemented sepD::escU(N262A) and sepD::escU(P263A) strains (expressing the respective escU allele from the chromosome) were generated by allelic exchange and were found to produce the same secretion profile as the respective plasmid complemented strains (Figure 4A). Immunoblotting with monoclonal anti-Tir antibodies revealed that Tir secretion occurred at variable levels

when EscU or EscU variants were expressed although for EscU(N262A), a novel lower molecular weight polypeptide was detected with anti-Tir antibodies (Figure 4B). This novel polypeptide species was consistently absent from ΔsepDΔescU/pJLT21 or pJLT23 and the parent ΔsepD strain. Figure 4 EscU auto-cleavage is required for efficient and stable effector secretion in an EPEC Δ sepD genetic background. (A) Left: Trans-complementation of ΔsepDΔescU with pJLT21 restored secretion Tubastatin A mouse of effectors to ΔsepD

levels while ΔsepDΔescU/pJLT22 did not restore normal effector secretion. ΔsepDΔescU/pJLT23 secreted a protein with an apparent molecular mass similar to Tir (asterisk). The dominant effector proteins are labelled and have been previously identified using mass spectrometry analyses [35]. Purified BSA was added to collected secreted fractions and served to aid in protein precipitation. Right: genomic integration of mutant escU alleles (cis-complementation, single copy) produces the same secretion phenotypes as the plasmid trans-complemented escU strains. Total secreted proteins were visualized by Coomassie G-250 staining. (B) Secreted protein preparations were analyzed by immunoblot with anti-Tir antibodies. Due

to the abundance of secreted Tir in ΔsepD and ΔsepDΔescU/pJLT21, (see Coomassie stain in panel A), only these samples were diluted 20 fold for immunoblotting purposes while the others were undiluted. A ΔsepDΔtir strain Orotidine 5′-phosphate decarboxylase (undiluted) was included to show the specificity of the anti-Tir antibodies. Lower molecular weight protein species are therefore Tir breakdown products that were consistently observed and recognized by the anti-Tir antibodies. A novel Tir polypeptide, indicated by an arrow, was exclusively detected in the lane containing secreted proteins derived from ΔsepDΔescU/pJLT22. CesT membrane localization is altered in the absence of EscU auto-cleavage In a previous report, we have demonstrated that the multicargo type III chaperone CesT mediates effector ‘docking’ at the inner membrane in an EscN-dependent manner [39]. CesT is also required for Tir stability in the EPEC cytoplasm [46, 47] and mediates efficient secretion of at least 9 type III effectors [39]. It has also been demonstrated that CesT contributes to effector translocation [42, 43].