Function and regulation of mitochondrial cytochrome c oxidase using mutant forms of the yeast enzyme

线粒体是我们细胞的主要能量供应者。它们的内膜中嵌入了一条蛋白质链-线粒体呼吸链-将食物新陈代谢产生的产物氧化，并将氧气还原为水。细胞色素c氧化酶(CcO)是催化氧还原反应的这一链的最后一个组成部分；事实上，正是这种酶负责消耗我们呼吸的大部分氧气，它提供了我们能量需求的很大一部分。能量在与氧气反应时释放，CcO能够通过在其所在的线粒体膜上产生电荷差来捕获能量-相当于给电子设备中的电容器充电。这种电荷梯度随后被另一种名为ATP合成酶的酶用来制造ATP。ATP是一种稳定的化学物质，在水解时可以释放能量；它扩散到细胞周围，提供我们细胞和组织健康运作所需的大量反应所需的大部分能量。我们已经知道了大量关于酶的原子结构以及它如何安全地与氧气反应释放能量的知识。我们对它利用能量使电荷梯度的一般方式也有很好的了解。然而，为了阐明耦合机制的具体细节，我们不得不在很大程度上依赖对更简单的细菌形式的酶的研究，特别是通过引入突变来改变这些细菌酶的个别部分的能力。然而，这样的细菌酶研究不能解决我们自己的人类，更复杂的，CcO如何工作的所有方面。几种不同类型的细菌CCOs的结构是已知的，但到目前为止，唯一已被解析的线粒体CcO结构是来自奶牛的心脏。尽管所有形式的CCO在氧气减少的区域周围都有类似的核心结构，但细菌和哺乳动物CCO之间的其他结构差异导致了能量储存反应与细菌CCO不同的说法。一个更显著的区别是线粒体CCOs有多达10个额外的亚基，其中没有一个是在细菌CCOs中发现的，到目前为止，我们对它们的功能知之甚少。也有很好的证据表明，与细菌的CCOs不同，在更复杂的生物体中，这些CCOs可以以不同的形式出现，并在不同组织的细胞环境中受到不同的调节。理解这些方面很重要，因为一系列人类遗传病是由CcO功能障碍引起的。不幸的是，由于缺乏一个好的系统来引入突变，这些独特的线粒体CcO问题的研究严重受阻。值得注意的是，存在于面包酵母细胞线粒体中的CcO在结构上与人类CcO线粒体在核心结构和所有附加亚基的结构上都非常相似。正因为如此，而且因为我们可以用成功处理细菌CCOS的相同方式对酵母CCOS的部分进行改变，所以我们现在可以研究这些线粒体(因此也就是人类)CCOS是如何发挥作用和受到控制的。对更复杂的线粒体酶的独特方面的了解将为测试和了解人类酶在健康和疾病中的功能和故障提供一个平台。

Mitochondria are the major energy providers of our cells. They have a chain of proteins - the mitochondrial respiratory chain - embedded in their inner membrane that oxidise products derived from the metabolism of food and reduce oxygen to water. Cytochrome c oxidase (CcO) is the final component of this chain that catalyses the oxygen reduction reaction; in fact, it is this enzyme that is responsible for consumption of most of the oxygen that we breathe and it provides a significant fraction of our energy needs. Energy is released during its reaction with oxygen and CcO is able to trap it by creating a charge difference across the mitochondrial membrane in which it is located - rather equivalent to charging of a capacitor in electronics. This charge gradient is then be used by another enzyme, called ATP synthase, to make ATP. ATP is a stable chemical that can release energy when it is hydrolysed; it diffuses around the cell and supplies a large part of energy needed by the myriad of reactions required for healthy functioning of our cells and tissues.We already know a great deal about the atomic structure of the enzyme and the way in which it safely reacts with oxygen to release energy. We also have a very good idea of the general way that it uses the energy to make the charge gradient. However, in order to elucidate the specific details of the coupling mechanism we have had to rely heavily on studies of simpler bacterial forms of the enzyme, particularly aided by the ability to change individual parts of these bacterial enzymes by introducing mutations. However, such bacterial enzyme studies cannot address all aspects of how our own human, more complicated, CcO works. The structures of several different types of bacterial CcOs are known but, to date, the only mitochondrial CcO structure that has been resolved is that from cow hearts. Although all forms of CcO share a similar core structure around the region where oxygen in reduced, other structural differences between bacterial and mammalian CcOs have led to suggestions that the energy storage reactions are different from those seen in bacterial CcOs.. An even more striking difference is that mitochondrial CcOs have up to 10 additional subunits, none of which are found in bacterial CcOs and to date we have little understanding of their functions. There is also good evidence that, in contrast to bacterial CcOs, those in more complex organisms can occur in different forms and are regulated differently in the cellular environments of different tissues. It is important to understand these aspects because a range of human genetic diseases arise from malfunctioning of CcO. Unfortunately, studies of these uniquely mitochondrial CcO questions are severely hampered by the lack of a good system to introduce mutations.Remarkably, the CcO that is present in mitochondria of Baker's yeast cells is structurally extremely similar to human CcO mitochondria in terms of both its core structure and the structures of all of its additional subunits. Because of this, and because we can make alterations in parts of yeast CcO in the same way as has been done successfully with bacterial CcOs, we can now investigate just how these mitochondrial (and therefore human) CcOs function and can be controlled. The understanding of the unique aspects of the more complex mitochondrial enzymes will provide a platform for testing and understanding how the human enzyme functions and malfunctions in health and disease.