Basu Malay K, Koonin Eugene V
National Center for Biotechnology Information, National Institutes of Health, Bethesda, Maryland 20894, USA.
Cell Cycle. 2005 Jul;4(7):947-52. doi: 10.4161/cc.4.7.1786. Epub 2005 Jul 25.
Sufiredoxin (Srx) is a sulfinic acid reductase, a recently identified eukaryotic enzyme, which is involved in the reduction of the hyperoxidized sulfinic acid form of the catalytic cysteine of 2-Cys peroxiredoxins (Prx). This reaction contributes to the oxidative stress response and H2O2 mediated signaling. We show that Srx has significant sequence and structural similarity to a functionally unrelated protein, ParB, a DNA-binding protein with a helix-turn-helix (HTH) domain which is involved in chromosome partitioning in bacteria. Sequence comparison and phylogenetic analysis of the Srx and ParB protein families suggest that Srx evolved via truncation of ParB, which removed the entire C-terminal half of the protein, including the HTH domain, and a substitution of cysteine for a glutamic acid in a highly conserved structural motif of ParB. The latter substitution apparently created the sulfinic acid reductase catalytic site. Evolution of a redox enzyme from a DNA-binding protein, with retention of highly significant sequence similarity, is unusual, even when compared to functional switches accompanying recruitment of other prokaryotic proteins for new functions in eukaryotes.
硫氧还蛋白（Srx）是一种亚磺酸还原酶，是最近发现的一种真核酶，它参与将2-半胱氨酸过氧化物酶（Prx）催化半胱氨酸的高度氧化亚磺酸形式还原。该反应有助于氧化应激反应和H2O2介导的信号传导。我们发现，Srx与一种功能不相关的蛋白质ParB具有显著的序列和结构相似性，ParB是一种具有螺旋-转角-螺旋（HTH）结构域的DNA结合蛋白，参与细菌中的染色体分配。Srx和ParB蛋白家族的序列比较和系统发育分析表明，Srx是通过ParB的截短进化而来的，截短过程去除了蛋白质的整个C端一半，包括HTH结构域，并且在ParB高度保守的结构基序中，半胱氨酸被谷氨酸取代。后一种取代显然创造了亚磺酸还原酶催化位点。从DNA结合蛋白进化出一种氧化还原酶，并保留高度显著的序列相似性，这是不寻常的，即使与真核生物中其他原核蛋白被招募用于新功能时伴随的功能转换相比也是如此。
