Ezraty Benjamin, Grimaud Régis, El Hassouni Mohammed, Moinier Daniéle, Barras Frédéric
Laboratoire de Chimie Bactérienne, Institut Fédératif de Recherche Biologie Structurale et Microbiologie, Centre National de la Recherche Scientifique, Marseille Cedex, France.
EMBO J. 2004 Apr 21;23(8):1868-77. doi: 10.1038/sj.emboj.7600172. Epub 2004 Apr 1.
In proteins, methionine residues are primary targets for oxidation. Methionine oxidation is reversed by methionine sulfoxide reductases A and B, a class of highly conserved enzymes. Ffh protein, a component of the ubiquitous signal recognition particle, contains a methionine-rich domain, interacting with a small 4.5S RNA. In vitro analyses reported here show that: (i) oxidized Ffh is unable to bind 4.5S RNA, (ii) oxidized Ffh contains methionine sulfoxide residues, (iii) oxidized Ffh is a substrate for MsrA and MsrB enzymes; and (iv) MsrA/B repairing activities allow oxidized Ffh to recover 4.5S RNA-binding abilities. In vivo analyses reveal that: (i) Ffh synthesized in the msrA msrB mutant contains methionine sulfoxide residues and is unstable, (ii) msrA msrB mutant requires high levels of Ffh synthesis for growth and (iii) msrA msrB mutation leads to defects in Ffh-dependent targeting of MalF. We conclude that MsrA and MsrB are required to repair Ffh oxidized by reactive oxygen species produced by aerobic metabolism, establishing an as-yet undescribed link between protein targeting and oxidation.
在蛋白质中，甲硫氨酸残基是氧化的主要靶点。甲硫氨酸氧化可被甲硫氨酸亚砜还原酶A和B逆转，这是一类高度保守的酶。Ffh蛋白是普遍存在的信号识别颗粒的一个组成部分，含有一个富含甲硫氨酸的结构域，可与一种小的4.5S RNA相互作用。本文报道的体外分析表明：（i）氧化的Ffh无法结合4.5S RNA，（ii）氧化的Ffh含有甲硫氨酸亚砜残基，（iii）氧化的Ffh是MsrA和MsrB酶的底物；以及（iv）MsrA/B修复活性使氧化的Ffh能够恢复4.5S RNA结合能力。体内分析显示：（i）在msrA msrB突变体中合成的Ffh含有甲硫氨酸亚砜残基且不稳定，（ii）msrA msrB突变体生长需要高水平的Ffh合成，以及（iii）msrA msrB突变导致Ffh依赖的MalF靶向缺陷。我们得出结论，MsrA和MsrB是修复由有氧代谢产生的活性氧氧化的Ffh所必需的，这在蛋白质靶向和氧化之间建立了一个尚未描述的联系。
