Transcriptional activation of in mediated by the XRE family member protein NceR.

Increasing antibiotic resistance of , the causative agent of gonorrhea, is a growing global concern that has renewed vaccine development efforts. The gonococcal OmpA protein was previously identified as a vaccine candidate due to its surface exposure, conservation, stable expression, and involvement in host-cell interactions. We previously demonstrated that the transcription of can be activated by the MisR/MisS two-component system. Interestingly, earlier work suggested that the availability of free iron also influences expression, which we confirmed in this study. In the present study, we found that iron regulation of was independent of MisR and searched for additional regulators. A DNA pull-down assay with the promoter from gonococcal lysates obtained from bacteria grown in the presence or absence of iron identified an XRE (Xenobiotic Response Element) family member protein encoded by . We found that an null mutant of strain FA19 displayed a reduced level of expression compared to the wild-type (WT) parent strain. Given this regulation, and the capacity of this XRE-like protein to regulate a gene involved in peptidoglycan biosynthesis (), along with its presence in other sp., we termed the encoded protein as NceR ( ell nvelope egulator). Critically, results from DNA-binding studies indicated that NceR regulates through a direct mechanism. Thus, expression is subject to both iron-dependent (NceR) and -independent (MisR/MisS) pathways. Hence, levels of the vaccine antigen candidate OmpA in circulating gonococcal strains could be influenced by transcriptional regulatory systems and the availability of iron. IMPORTANCE Herein, we report that the gene encoding a conserved gonococcal surface-exposed vaccine candidate (OmpA) is activated by a heretofore undescribed XRE family transcription factor, which we term NceR. We report that NceR regulation of expression in is mediated by an iron-dependent mechanism, while the previously described MisR regulatory system is iron-independent. Our study highlights the importance of defining the complexity of coordinated genetic and physiologic systems that regulate genes encoding vaccine candidates to better understand their availability during infection.