Structural and functional properties of a single domain hemoglobin from the food-borne pathogen Campylobactor jejuni.
Structural and functional properties of a single domain hemoglobin from the food-borne pathogen Campylobactor jejuni.
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食源性病原体空肠弯曲菌单域血红蛋白的结构和功能特性。
DOI：
10.1074/jbc.m704415200
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Lu C
中科院分区：
文献类型：
--
作者：
Lu C
空肠弯曲菌含有两种球蛋白，一种截短的血红蛋白Ctb和一种单结构域血红蛋白Cgb。Ctb的生理功能尚不清楚，而Cgb与NO解毒有关。利用共振拉曼散射，在251 cm-1处鉴定了Cgb的铁-组氨酸伸缩模式。该频率异常高，表明作为连接涉及F8 His、H23 Glu和G5 Tyr残基的催化三联体的H-键合网络的结果，近端组氨酸具有咪唑特征。在CO络合物中，确定了两种构象，其νC-O/ν Fe-CO在529/1914 cm-1和492/1963 cm-1处。前者被分配到一个“封闭”的构象，其中血红素结合的CO是稳定的H-键（S）捐赠的B10 Tyr-E7 Gln残基，而后者被分配到一个“开放”的构象，其中H-键的相互作用是不存在的。两种不同构象的存在证明了蛋白质基质的可塑性。在O2-复合物中，铁-O2伸缩频率在554 cm-1处，这是异常低的，表明血红素结合的O2通过B10 Tyr-E7 Gln残基提供的强H-键稳定。这种情况与其低O2释放速率（0.87 s-1）一致。总之，数据表明Cgb的NO解毒活性是由近端F8 His的咪唑酯特征和由B10 Tyr-E7 Gln提供的远端正极性环境促进的。它们可以分别为假定的过氧亚硝酸盐中间体异构化为产物硝酸盐所需的O-O键裂解反应提供电子“推”和“拉”。
Campylobacter jejunicontains 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 νC-O/νFe-COat 529/1914 cm-1and 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-O2stretching frequency was identified at 554 cm-1, which is unusually low, indicating that the heme-bound O2is stabilized by strong H-bond(s) donated by the B10Tyr-E7Gln residues. This scenario is consistent with its low O2off-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.