The methylaspartate cycle in haloarchaea and its possible role in carbon metabolism
The methylaspartate cycle in haloarchaea and its possible role in carbon metabolism
复制标题
盐古菌中的甲基天冬氨酸循环及其在碳代谢中的可能作用
DOI：
10.1038/ismej.2015.132
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发表时间：
2016-03-01
期刊：
影响因子：
11
通讯作者：
Berg, Ivan A.
中科院分区：
文献类型：
--
作者：
Borjian, Farshad;Han, Jing;Berg, Ivan A.
盐古菌（Halobacteria）生活在极其嗜盐的条件下，并进化出许多独特的代谢特征，这有助于它们适应环境。甲基天冬氨酸循环是最近提出的 Haloarcula marismortui 的一种回补乙酸同化途径，是这些特殊适应之一。在此循环中，乙酰辅酶A通过作为特征中间体的甲基天冬氨酸被氧化为乙醛酸。随后乙醛酸与另一个乙酰辅酶A分子缩合产生苹果酸，这是合成代谢的起始底物。循环功能的提议主要基于体外数据，留下了有关所涉及的酶学和嗜盐古菌中循环的发生的几个悬而未决的问题。使用H的基因缺失突变体。西班牙、酶测定和代谢物分析，我们现在通过明确鉴定编码循环中所有特征酶的基因来缩小这些差距。基于这些结果，我们能够对盐古菌中甲基天冬氨酸循环和替代乙酸同化策略（乙醛酸循环）的分布进行深入研究。我们发现这两个周期在盐古菌中均匀分布。有趣的是，83% 使用甲基天冬氨酸循环的物种还拥有聚羟基脂肪酸酯生物合成的基因，而只有 34% 使用乙醛酸循环的物种能够合成这种储存化合物。这一发现表明，甲基天冬氨酸循环是为了在碳饥饿期间利用聚羟基脂肪酸酯而形成的，而乙醛酸循环可能适合在通过乙酰辅酶A代谢的底物上生长。
Haloarchaea (classHalobacteria) live in extremely halophilic conditions and evolved many unique metabolic features, which help them to adapt to their environment. The methylaspartate cycle, an anaplerotic acetate assimilation pathway recently proposed forHaloarcula marismortui, is one of these special adaptations. In this cycle, acetyl-CoA is oxidized to glyoxylate via methylaspartate as a characteristic intermediate. The following glyoxylate condensation with another molecule of acetyl-CoA yields malate, a starting substrate for anabolism. The proposal of the functioning of the cycle was based mainly onin vitrodata, leaving several open questions concerning the enzymology involved and the occurrence of the cycle in halophilic archaea. Using gene deletion mutants ofH. hispanica, enzyme assays and metabolite analysis, we now close these gaps by unambiguous identification of the genes encoding all characteristic enzymes of the cycle. Based on these results, we were able to perform a solid study of the distribution of the methylaspartate cycle and the alternative acetate assimilation strategy, the glyoxylate cycle, among haloarchaea. We found that both of these cycles are evenly distributed in haloarchaea. Interestingly, 83% of the species using the methylaspartate cycle possess also the genes for polyhydroxyalkanoate biosynthesis, whereas only 34% of the species with the glyoxylate cycle are capable to synthesize this storage compound. This finding suggests that the methylaspartate cycle is shaped for polyhydroxyalkanoate utilization during carbon starvation, whereas the glyoxylate cycle is probably adapted for growth on substrates metabolized via acetyl-CoA.