Institut National de la Recherche Agronomique, Institut Micalis, UMR 1319, 78352 Jouy-en-Josas, France.
J Biol Chem. 2010 May 21;285(21):16032-41. doi: 10.1074/jbc.M109.024505. Epub 2010 Mar 22.
Heme is a redox-reactive molecule with vital and complex roles in bacterial metabolism, survival, and virulence. However, few intracellular heme partners were identified to date and are not well conserved in bacteria. The opportunistic pathogen Streptococcus agalactiae (group B Streptococcus) is a heme auxotroph, which acquires exogenous heme to activate an aerobic respiratory chain. We identified the alkyl hydroperoxide reductase AhpC, a member of the highly conserved thiol-dependent 2-Cys peroxiredoxins, as a heme-binding protein. AhpC binds hemin with a K(d) of 0.5 microm and a 1:1 stoichiometry. Mutagenesis of cysteines revealed that hemin binding is dissociable from catalytic activity and multimerization. AhpC reductase activity was unchanged upon interaction with heme in vitro and in vivo. A group B Streptococcus ahpC mutant displayed attenuation of two heme-dependent functions, respiration and activity of a heterologous catalase, suggesting a role for AhpC in heme intracellular fate. In support of this hypothesis, AhpC-bound hemin was protected from chemical degradation in vitro. Our results reveal for the first time a role for AhpC as a heme-binding protein.
血红素是一种具有重要且复杂功能的氧化还原反应分子，参与细菌的代谢、存活和毒力。然而，迄今为止，只有少数细胞内血红素伴侣被鉴定出来，而且在细菌中也没有很好的保守性。机会性病原体无乳链球菌（B 群链球菌）是一种血红素营养缺陷型细菌，需要从外部获取血红素来激活有氧呼吸链。我们鉴定了烷基氢过氧化物还原酶 AhpC，它是高度保守的硫依赖 2-Cys 过氧化物酶家族的成员，是一种血红素结合蛋白。AhpC 与血红素的结合具有 0.5 微米的 K(d)值和 1:1 的化学计量比。半胱氨酸突变显示，血红素结合与催化活性和多聚化是可分离的。AhpC 还原酶的活性在体外和体内与血红素相互作用时没有变化。B 群链球菌 ahpC 突变体显示出两种血红素依赖性功能的衰减，即呼吸作用和异源过氧化氢酶的活性，这表明 AhpC 在血红素细胞内命运中发挥作用。为了支持这一假设，体外实验表明 AhpC 结合的血红素受到了保护，不会受到化学降解。我们的研究结果首次揭示了 AhpC 作为血红素结合蛋白的作用。
