The obligate anaerobe Porphyromonas gingivalis is the etiological agent responsible for periodontal disease. It must withstand high levels of reactive nitrogen species in the oral cavity generated by the host and other oral flora. The mechanisms allowing for protection against such stress remain poorly understand. HcpR is an FNR-CRP family regulator that has been implicated in regulation of the nitrosative stress response. In this study we characterize the biochemical properties of HcpR. It is a homo-dimer that is composed of 3 domains – a heme-binding domain, dimerization helix, and a DNA-binding domain. Our studies show that HcpR binds the heme cofactor. UV-Vis and Raman spectroscopy reveal that the bound heme is capable of binding the diatomic gas molecule Nitric Oxide (NO)-a source of nitrosative stress. Binding of NO causes a change in the oxidation state of the iron. SAXS reveals the protein bears a structural resemblance to homology models generated from an ortholog. Promoterr studies reveal that mechanisms P. gingivalis-HcpR uses to modulate expression are novel and different than those found in E. coli and P. aeruginosa.