Structural and functional properties of a single domain hemoglobin from the food-borne pathogen Campylobactor jejuni.
Campylobacter jejuni contains two globins, a truncated hemoglobin, Ctb, and a single domain hemoglobin, Cgb. The physiological function of Ctb remains unclear, whereas Cgb has been linked to NO detoxification. With resonance Raman scattering, the iron-histidine stretching mode of Cgb was identified at 251 cm(-1). This frequency is unusually high, suggesting an imidazolate character of the proximal histidine as a result of the H-bonding network linking the catalytic triad involving the F8His, H23Glu, and G5Tyr residues. In the CO-complex, two conformers were identified with the nuC-O/nuFe-CO at 529/1914 cm(-1) and 492/1963 cm(-1). The former is assigned to a "closed" conformation, in which the heme-bound CO is stabilized by the H-bond(s) donated from the B10Tyr-E7Gln residues, whereas the latter is assigned to an "open" conformer, in which the H-bonding interaction is absent. The presence of the two alternative conformations demonstrates the plasticity of the protein matrix. In the O2-complex, the iron-O2 stretching frequency was identified at 554 cm(-1), which is unusually low, indicating that the heme-bound O2 is stabilized by strong H-bond(s) donated by the B10Tyr-E7Gln residues. This scenario is consistent with its low O2 off-rate (0.87 s(-1)). Taken together the data suggest that the NO-detoxifying activity of Cgb is facilitated by the imidazolate character of the proximal F8His and the distal positive polar environment provided by the B10Tyr-E7Gln. They may offer electronic "push" and "pull," respectively, for the O-O bond cleavage reaction required for the isomerization of the presumed peroxynitrite intermediate to the product, nitrate.
Lu
Changyuan
C
Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Mukai
Masahiro
M
Lin
Yu
Y
Wu
Guanghui
G
Poole
Robert K
RK
Yeh
Syun-Ru
SR
D000596:Amino Acids / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins; D001665:Binding Sites; D016123:Campylobacter jejuni / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D005516:Food Microbiology; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D009569:Nitric Oxide / Q000737:chemistry* / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D013059:Spectrum Analysis, Raman; D013329:Structure-Activity Relationship; D054793:Truncated Hemoglobins
D000596:Amino Acids; D001426:Bacterial Proteins; C489659:Cgb protein, Campylobacter jejuni; D006454:Hemoglobins; D054793:Truncated Hemoglobins; D009569:Nitric Oxide; D010100:Oxygen