Secretion of early and late substrates of the type III secretion system from Xanthomonas is controlled by HpaC and the C-terminal domain of HrcU.
Bottom Line: T3S substrate specificity is controlled by HpaC, which promotes secretion of translocon and effector proteins but prevents efficient secretion of the early substrate HrpB2.The results of mutant studies showed that cleavage of HrcU contributes to pathogenicity and secretion of late substrates but is dispensable for secretion of HrpB2, which is presumably secreted prior to HrcU cleavage.As HrcU(Y318D) did not interact with HrpB2 and HpaC, we propose that the substrate specificity switch leads to the release of HrcU(C) -bound HrpB2 and HpaC.
Affiliation: Institute of Biology, Department of Genetics, Martin-Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany.Show MeSH
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Mentions: In addition to HpaC, GST–HrcU255–357 also interacts with a C-terminally c-Myc epitope-tagged derivative of the early T3S substrate HrpB2 (Lorenz et al., 2008b). To investigate whether the NPTH motif of HrcU contributes to the interaction between HrcUC and HrpB2, we performed additional pull-down assays with GST or GST–HrcU derivatives as described above. When GST–HrcU fusion proteins were immobilized on glutathione sepharose and incubated with HrpB2-c-Myc, we detected HrpB2-c-Myc in the eluate of GST–HrcU255–357 as expected but not in the eluates of GST–HrcU265–357 and GST–HrcU268–357 (Fig. 6A; Lorenz et al., 2008b). The presence of N264A and P265A point mutations in GST–HrcU255–357, respectively, did not significantly affect the binding of HrpB2-c-Myc (Fig. 6B). In contrast, HrpB2-c-Myc was not detected in the eluate of GST–HrcU255–357/P265G indicating that the P265G exchange abolishes the stable interaction between GST–HrcU255–357 and HrpB2 (Fig. 6B).
Affiliation: Institute of Biology, Department of Genetics, Martin-Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany.