The Neisseria gonorrhoeae cytochrome c2-bacterial peroxidase electron-transfer complex is competent in hydrogen peroxide reduction

Neisseria gonorrhoeae is a pathogenic bacterium responsible for the disease gonorrhea, which has gained increasing attention in recent years due to the emergence of strains resistant to the currently used antibiotics. In the absence of a vaccine, understanding mechanisms that contribute to infection is imperative. One such mechanism is the reduction of hydrogen peroxide by the outer membrane bound bacterial peroxidase. Here, steady-state kinetics shows that cytochrome c₂, previously implicated in nitrite reduction, is an efficient electron donor to this enzyme, proving to be an alternative to the lipid-modified azurin. The cytochrome c₂-mediated peroxidase activity has a K_M of 0.74 ± 0.08 μM and a k_obs of 18 ± 1 s^-1 for hydrogen peroxide, with an optimum pH at 7.7. The pH and ionic-strength dependence of this activity differs from that of azurin, suggesting that the two electron donors can play complementary roles depending on external conditions. Furthermore, the viscosity dependence of the activity suggests that protein-protein interactions are not purely diffusion-controlled but also governed by conformational changes required for complex formation and/or electron transfer, and docking analysis implies that cytochrome c₂ binds near the exposed edge of the electron transferring heme of the bacterial peroxidase. This study improves our understanding of the periplasmic physiology of N. gonorrhoeae by demonstrating how the pathogen's flexibility in using electron donors enables it to maintain peroxidase activity and cope with oxidative stress in different host environments. These insights could inform future strategies aimed at disrupting redox homeostasis to combat antibiotic-resistant strains.