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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