Neisseria gonorrhoeae is an obligate human pathogen that causes the common STI gonorrhea, which presents a growing threat to global health. The WHO estimated 78 million new cases of gonorrhea worldwide in 2017, with estimates of 820,000 new cases in the United States alone according to the CDC. High-frequency phase and antigenic variation inherent in N. gonorrhoeae, coupled with its natural ability to rapidly acquire and stably integrate antimicrobial resistance factors into its genome, have culminated in an infection against which there is no effective vaccine, and for which the list of viable therapeutic options is quickly shrinking. Moreover, no protective immunity against subsequent infections is elicited upon exposure to N. gonorrhoeae, which highlights the need for research of novel antimicrobial and vaccination strategies. Within the human host, N. gonorrhoeae utilizes a unique strategy to overcome host sequestration of essential nutrients – termed nutritional immunity (NI) – such as ions of trace metals. The pathogen produces a family of outer membrane proteins called TonB-dependent transporters (TdTs) capable of binding to host NI factors and stripping them of their nutritional cargo for use by the pathogen. Importantly, these TdTs are very highly conserved and expressed among Neisseria species. TbpA is a well-characterized TdT that allows N. gonorrhoeae to acquire iron from human transferrin, and recent studies from our lab have shown that TdfH is capable of binding to a zinc-sequestering S100 protein called calprotectin and stripping it of its zinc ion. The S100 proteins are EF-hand calcium-binding proteins that naturally play an integral role in Ca2+ homeostasis, but due to their ability to bind transition metals, they have also demonstrated an innate immunity role by participating in nutrient sequestration.
The S100 proteins are expressed in all human cells, and all are capable of binding transition metals including zinc, manganese, and cobalt. Calprotectin, S100A7, and S100A12 have demonstrated an ability to hinder the infection potential of pathogenic E. coli, S. aureus, C. albicans, and various other pathogens via zinc sequestration. Herein, we demonstrate that N. gonorrhoeae is able to overcome this phenomenon and actually utilize these proteins as a zinc source in vitro. Furthermore, we identify S100A7 as the specific ligand for TdfJ, which utilizes this ligand to internalize zinc during infection. S100A7 growth support in vitro is dependent upon a functional TonB, TdfJ, and the cognate ABC transport system ZnuABC, and isogenic mutants incapable of producing znuA or tdfJ recover S100A7 utilization by complementation. Whole-cell binding assays and affinity pulldowns show that S100A7 binds specifically to both gonococcal and recombinant TdfJ, and growth and binding experiments show that these described phenomena are specific to human and not mouse S100A7. Finally, we show that a His-Asn double mutant S100A7 that is incapable of binding zinc cannot be utilized for growth by gonococci. These data illustrate the unique nature of the gonococcus’ ability to co-opt host defense strategies for its own purposes, and further identify the TdTs as promising targets for strategies to combat and prevent gonococcal infection.
| Identifer | oai:union.ndltd.org:vcu.edu/oai:scholarscompass.vcu.edu:etd-6800 |
| Date | 01 January 2019 |
| Creators | Maurakis, Stavros |
| Publisher | VCU Scholars Compass |
| Source Sets | Virginia Commonwealth University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | © The Author |
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