Characterisation and Inhibition of Carnitine Biosynthesis Oxygenases

脂肪酸是人类和大多数其他生命形式的主要能量来源。为了使脂肪酸代谢，它们必须被运送到称为线粒体的细胞内隔室中，在那里它们通过依赖氧气的呼吸过程进行代谢，产生对我们所做的一切都至关重要的化学能。然而，当我们摄入的脂肪酸超过代谢能力时，它们就会被储存起来，导致体重增加，最终导致肥胖和相关疾病。脂肪酸运输到线粒体的过程需要它们与一种叫做肉碱的分子结合，这样命名是因为肉碱在动物肌肉中含量很高。我们人类都能制造肉毒碱并从我们的饮食中获取。肉碱被广泛用作膳食补充剂，因为它能促进脂肪代谢。人体产生肉毒碱的起点是蛋白质，这些蛋白质被降解成一种不寻常的氨基酸，叫做三甲基赖氨酸（TML）。TML通过一系列酶催化步骤转化为肉碱，其中两个步骤是由加氧酶催化的，即利用氧进行催化的酶。米屈酸钠是一种临床使用的化合物，它能抑制这些加氧酶中的至少一种。米屈酸钠是在心脏病发作后给病人服用，以抑制脂肪酸的生物合成。这是因为脂肪酸的生物合成会产生有害的活性氧化物质作为副产物，这些物质被认为在心脏病发作后特别危险。我们最近在了解米屈酸钠如何通过解决其目标的晶体结构起作用的工作上取得了突破。我们还发现，米屈酸盐不是一种简单的酶抑制剂，事实上，它是一种底物，正在经历一种前所未有的反应，包括其分子结构的重排。这项工作也使我们处于一个非常有利的位置，来了解米屈酸盐是如何在人体细胞中起作用的，并揭开我们和其他动物如何制造肉毒碱的分子细节。我们对探索肉毒碱生物合成和遗传学之间的联系特别感兴趣，因为当它存在于称为组蛋白的DNA结合蛋白中时，TML还参与调节细胞中哪些基因“打开和关闭”。重要的是，我们有充分的证据表明，我们可以开发出改良版的米屈酸盐，我们将把它提供给对脂肪酸代谢感兴趣的广大研究人员。我们将研究肉毒碱生物合成加氧酶的结构和机制，并开发改进的抑制剂，这些抑制剂将作为肉毒碱生物合成加氧酶生理作用的功能探针。在我们发现肉碱生物合成酶的不寻常化学性质的基础上，我们还将评估它们在生产将用于制药工业的化学品方面的潜力。

Fatty acids are a major energy source for humans and most other life forms. In order for fatty acids to be metabolised they must be transported into intracellular compartments called mitochondria, where they are metabolised by the oxygen dependent process of respiration to generate chemical energy that is essential for absolutely everything we do. However, when we consume more fatty acids than we can metabolise they are stored, leading to weight gain and, ultimately, obesity and related diseases. The process of fatty acid transport into mitochondria requires their conjugation to a molecule called carnitine, so named because it is present at high levels in animal muscle, i.e. meat. We humans both make carnitine and obtain it from our diet. Carnitine is widely used as a dietery supplement because it promotes fat metabolism. The starting points for carnitine production in humans are proteins that are degraded to give an unusual amino acid called trimethyl-lysine or TML. TML is converted into carnitine by a series of enzyme-catalysed steps, two of which are catalysed by oxygenases, i.e. enzymes that use oxygen for catalysis. Mildronate, a clinically used compound, inhibits at least one of these oxygenases. Mildronate is given to patients after they have had a heart attack, in order to inhibit fatty acid biosynthesis. This is because fatty acid biosynthesis produces damaging reactive oxidising species as byproducts and these are thought to be particularly dangerous after heart attacks. We have recently made a breakthrough in work aimed at understanding how Mildronate works by solving crystal structures of its target. We have also found that Mildronate is not a simple enzyme inhibitor but is, in fact, a substrate undergoing an unprecedented reaction involving rearrangement of its molecular structure. This work has also placed us in an exceptionally good position to understand how Mildronate actually works in human cells and to unravel the molecular details of how we and other animals make carnitine. We are particularly interested in exploring links between carnitine biosynthesis and genetics because, when it is present in DNA binding proteins called histones, TML is also involved in regulating which genes are 'turned on and off' in cells. Importantly we have good evidence that we can develop improved versions of Mildronate, which we will make available to the large community of researchers interested in fatty acid metabolism. We will investigate the structure and mechanism of the oxygenases of carnitine biosynthesis and develop improved inhibitors that will be useful as functional probes for the physiological roles of the carnitine biosynthesis oxygenases. Building upon our discovery the unusual chemistry of the carnitine biosynthesis enzymes, we will also evaluate their potential for the production of chemicals that will be of use to the pharmaceutical industry.