Department of Microbiology, University of Illinois, 601 S. Goodwin Ave, Urbana, IL, 61801, USA.
Department of Microbiology, University of Illinois, 601 S. Goodwin Ave, Urbana, IL, 61801, USA.
Free Radic Biol Med. 2019 Aug 20;140:4-13. doi: 10.1016/j.freeradbiomed.2019.01.048. Epub 2019 Feb 6.
Biochemical mechanisms emerged and were integrated into the metabolic plan of cellular life long before molecular oxygen accumulated in the biosphere. When oxygen levels finaly rose, they threatened specific types of enzymes: those that use organic radicals as catalysts, and those that depend upon iron centers. Nature has found ways to ensure that such enzymes are still used by contemporary organisms. In some cases they are restricted to microbes that reside in anoxic habitats, but in others they manage to function inside aerobic cells. In the latter case, it is frequently true that the ancestral enzyme has been modified to fend off poisoning. In this review we survey a range of protein adaptations that permit radical-based and low-potential iron chemistry to succeed in oxic environments. In many cases, accessory domains shield the vulnerable radical or metal center from oxygen. In others, the structures of iron cofactors evolved to less oxidizable forms, or alternative metals replaced iron altogether. The overarching view is that some classes of biochemical mechanism are intrinsically incompatible with the presence of oxygen. The structural modification of target enzymes is an under-recognized response to this problem.
生物化学机制在分子氧在生物圈中积累之前很久就已经出现并融入了细胞生命的新陈代谢计划中。当氧气水平最终上升时，它们会威胁到特定类型的酶：那些使用有机自由基作为催化剂的酶，以及那些依赖铁中心的酶。大自然已经找到了确保这些酶仍然被现代生物利用的方法。在某些情况下，它们仅限于生活在缺氧环境中的微生物，但在其他情况下，它们设法在需氧细胞内发挥作用。在后一种情况下，通常情况下，原始酶已经被修改以抵御中毒。在这篇综述中，我们调查了一系列蛋白质适应机制，这些机制允许基于自由基和低势能铁化学在有氧环境中取得成功。在许多情况下，辅助结构域将易受攻击的自由基或金属中心与氧气隔离。在其他情况下，铁辅因子的结构演变为更不易氧化的形式，或者完全用其他金属替代铁。总的来说，有些类别的生化机制本质上与氧气的存在不相容。目标酶的结构修饰是对这一问题的一种认识不足的反应。
