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首页> 外文期刊>Journal of bacteriology >Methionine Sulfoxide Reductase from the Hyperthermophilic Archaeon Thermococcus kodakaraensis, an Enzyme Designed To Function at Suboptimal Growth Temperatures
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Methionine Sulfoxide Reductase from the Hyperthermophilic Archaeon Thermococcus kodakaraensis, an Enzyme Designed To Function at Suboptimal Growth Temperatures

机译：来自超嗜热古细菌热球菌kodakaraensis的蛋氨酸亚砜还原酶，该酶被设计为在最适生长温度下发挥作用的酶

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Methionine sulfoxide reductase (Msr) catalyzes the thioredoxin-dependent reduction and repair of methionine sulfoxide (MetO). Although Msr genes are not present in most hyperthermophile genomes, an Msr homolog encoding an MsrA-MsrB fusion protein (MsrABTk) was present on the genome of the hyperthermophilic archaeon Thermococcus kodakaraensis. Recombinant proteins corresponding to MsrABTk and the individual domains (MsrATk and MsrBTk) were produced, purified, and biochemically examined. MsrATk and MsrBTk displayed strict substrate selectivity for Met-S-O and Met-R-O, respectively. MsrABTk, and in particular the MsrB domain of this protein, displayed an intriguing behavior for an enzyme from a hyperthermophile. While MsrABTk was relatively stable at temperatures up to 80°C (with a half-life of ～30 min at 80°C), a 75% decrease in activity was observed after 2.5 min at 85°C, the optimal growth temperature of this archaeon. Moreover, maximal levels of MsrB activity of MsrABTk were observed at the strikingly low temperature of 30°C, which also was observed for MsrBTk. Consistent with the low-temperature-specific biochemical properties of MsrABTk, the presence of the protein was greater in T. kodakaraensis cells grown at suboptimal temperatures (60 to 70°C) and could not be detected at 80 to 90°C. We found that the amount of intracellular MsrABTk protein increased with exposure to higher dissolved oxygen levels, but only at suboptimal growth temperatures. While measuring background rates of the Msr enzyme reactions, we observed significant levels of MetO reduction at high temperatures without enzyme. The occurrence of nonenzymatic MetO reduction at high temperatures may explain the specific absence of Msr homologs in most hyperthermophiles. Together with the fact that the presence of Msr in T. kodakaraensis is exceptional among the hyperthermophiles, the enzyme may represent a novel strategy for this organism to deal with low-temperature environments in which the dissolved oxygen concentrations increase.
机译：蛋氨酸亚砜还原酶（Msr）催化依赖硫氧还蛋白的还原和修复蛋氨酸亚砜（MetO）。尽管在大多数嗜热嗜热菌基因组中不存在Msr基因，但在嗜热古细菌 Thermococcus kodakaraensis 的基因组中仍存在一个编码MsrA-MsrB融合蛋白（MsrAB Tk ）的Msr同源物。 。产生，纯化和生化检查对应于MsrAB Tk 和各个结构域（MsrA Tk 和MsrB Tk ）的重组蛋白。 MsrA Tk 和MsrB Tk 对Met- S -O和Met- R -O具有严格的底物选择性，分别。 MsrAB Tk ，尤其是该蛋白的MsrB结构域，对嗜热嗜热菌中的酶表现出令人着迷的行为。尽管MsrAB Tk 在高达80°C的温度下相对稳定（在80°C下的半衰期为〜30分钟），但在85°C下2.5分钟后观察到活性降低了75％。 C，这个古细菌的最佳生长温度。此外，在极低的30°C温度下观察到了MsrAB Tk 的最大MsrB活性，MsrB Tk 也观察到了最高水平。与MsrAB Tk 的低温特异性生化特性一致， T中蛋白质的存在更大。 kodakaraensis 细胞在次适温（60至70°C）下生长，在80至90°C下无法检测到。我们发现，细胞内MsrAB Tk 蛋白的量随着暴露于更高的溶解氧水平而增加，但仅在次适生长温度下才增加。在测量Msr酶反应的背景速率时，我们观察到在没有酶的情况下，高温下MetO的还原水平显着。高温下非酶法MetO还原的发生可能解释了大多数嗜热菌中Msr同源物的特定缺失。以及 T中Msr的存在。嗜碱菌在高温嗜热菌中是例外，该酶可能代表了该生物应对溶解氧浓度升高的低温环境的一种新策略。

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