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J. Biol. Chem., Vol. 282, Issue 35, 25917-25928, August 31, 2007

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Structural and Functional Properties of a Single Domain Hemoglobin from the Food-borne Pathogen Campylobactor jejuni^*

Changyuan Lu, Masahiro Mukai, Yu Lin, Guanghui Wu^¶, Robert K. Poole^¶, and Syun-Ru Yeh¹

From the Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, the Mitsubishi Kagaku Institute of Life Sciences, Minamiooya, Machida, Tokyo 194-8511, Japan, and the ^¶Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, S10 2TN United Kingdom

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 _C-O/_Fe-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.

Received for publication, May 30, 2007 , and in revised form, July 2, 2007.

^* This work is supported by National Institutes of Health Grant HL65465 (to S.-R. Y.) and a Biotechnology and Biological Sciences Research Council (BBSRC, United Kingdom) Grant (to R. K. P.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY 10461. Tel.: 718-430-4234; Fax: 718-430-4230; E-mail: syeh{at}aecom.yu.edu.

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