一种来自结核分枝杆菌的具有协同氧结合能力的血红蛋白。
A cooperative oxygen-binding hemoglobin from Mycobacterium tuberculosis.
作者信息
Couture M, Yeh S R, Wittenberg B A, Wittenberg J B, Ouellet Y, Rousseau D L, Guertin M
机构信息
Department of Biochemistry, Faculty of Sciences and Engineering, Laval University, Quebec, QC Canada G1K 7P4.
出版信息
Proc Natl Acad Sci U S A. 1999 Sep 28;96(20):11223-8. doi: 10.1073/pnas.96.20.11223.
Two putative hemoglobin genes, glbN and glbO, were recently discovered in the complete genome sequence of Mycobacterium tuberculosis H37Rv. Here, we show that the glbN gene encodes a dimeric hemoglobin (HbN) that binds oxygen cooperatively with very high affinity (P(50) = 0.013 mmHg at 20 degrees C) because of a fast combination (25 microM(-1).s(-1)) and a slow dissociation (0.2 s(-1)) rate. Resonance Raman spectroscopy and ligand association/dissociation kinetic measurements, along with mutagenesis studies, reveal that the stabilization of the bound oxygen is achieved through a tyrosine at the B10 position in the distal pocket of the heme with a conformation that is unique among the globins. Physiological studies performed with Mycobacterium bovis bacillus Calmette-Guérin demonstrate that the expression of HbN is greatly enhanced during the stationary phase in aerobic cultures but not under conditions of limited oxygen availability. The results suggest that, physiologically, the primary role of HbN may be to protect the bacilli against reactive nitrogen species produced by the host macrophage.
最近在结核分枝杆菌H37Rv的全基因组序列中发现了两个假定的血红蛋白基因，即glbN和glbO。在此，我们表明glbN基因编码一种二聚体血红蛋白（HbN），它以非常高的亲和力协同结合氧气（20℃时P(50)=0.013 mmHg），这是由于其快速结合（25 μM⁻¹·s⁻¹）和缓慢解离（0.2 s⁻¹）速率。共振拉曼光谱、配体结合/解离动力学测量以及诱变研究表明，结合氧的稳定是通过血红素远端口袋中B10位置的酪氨酸实现的，其构象在球蛋白中是独特的。用卡介苗进行的生理学研究表明，HbN的表达在需氧培养的稳定期大大增强，但在氧气供应有限的条件下则不然。结果表明，在生理上，HbN的主要作用可能是保护杆菌免受宿主巨噬细胞产生的活性氮物质的侵害。
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