Significance of Knotted Structures for Function of Proteins and Nucleic Acids - September 17-21, 2014

Significance of Knotted Structures for Function of Proteins and Nucleic Acids

Poster Session I

3 – POS Board 3 HcpR of Porphyromonas gingivalis Utilizes Heme to Bind Nitric Oxide Benjamin Belvin , Janina P. Lewis. Virginia Commonwealth University, Richmond, USA.

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 members of the oral flora. HcpR is a putative FNR-CRP family regulator that has been implicated in regulation of the nitrosative stress response in P. gingivalis. Objective : Characterizing the structural and biochemical properties HcpR will garner a better understanding of the mechanisms HcpR utilizes in its role as a regulator of the nitrosative stress resposne P. gingivalis . Methods : To characterize the biochemical and structural properties of HcpR small angle X-ray scattering, analytical ultracentrifugation, circular dichroism, bioinformatics, UV-Vis spectroscopy, and resonance raman spectroscopy were utilized. Results : HcpR is a homo-dimer that is composed of three domains – a heme-binding domain, dimerization helix, and a DNA-binding domain. Our studies show that HcpR binds the heme cofactor. Bound heme is capable of binding the diatomic gas molecule NO. As shown by UV-Vis and Raman specrtroscopy, binding of NO causes a change in the oxidation state of the iron. Finally, our SAXS data shows that the protein bears a structural resemblance to the crystal structure of Dnr, an FNR-CRP regulator of nitrosaitve stress that binds heme in Pseudomonas aeruginosa . Conclusion : HcpR exists as a dimer in solution and bears a structural resemblance to the FNR-CRP family of bacterial regulators. Binding of heme to HcpR allows the protein to specifically bind NO that in turn reduces Fe(3+) to Fe(2+) thus leading to structural rearangment of the protein.

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