Bacterial sphingolipids - revealing hidden biosynthetic pathways of key players in host-microbe interactions.

动物和细菌细胞有一个保护性的、防水的外壳，它是由一个亲水的头基团和一个长而憎水的尾巴组成的。这个大家族的分子被称为脂质，包括常见的东西，如饱和/不饱和脂肪和胆固醇。一种特殊的脂类亚家族被称为鞘脂（SLs）及其更复杂的神经酰胺版本（它们有两条脂肪尾部）。SLs不仅在细胞膜的外壳中起结构作用，使细胞膜抵抗水分，让营养物质进出；它们还能刺激人体免疫系统。SL水平是动态的，但也受到严格控制——细胞SL水平的任何增加或减少都是出了问题的迹象。SL水平的变化与老年和阿尔茨海默氏症、糖尿病、哮喘、癌症和神经损耗性疾病等疾病密切相关。一个对人类健康有直接影响的令人兴奋的研究领域是发现人类是许多不同类型细菌的宿主——这些细菌统称为微生物群/微生物组。目前的估计是，我们身体里的每一个细胞，都有一个细菌细胞。这些细菌可能是“坏的”并导致疾病（例如超级细菌），但大多数是“好”细菌，对我们的健康有益。这些细菌生活在我们的口腔、皮肤和肠道中，帮助我们代谢食物，也被认为起着保护作用。一个令人惊讶的发现是，与我们生活在一起的细菌产生的分子允许细菌和人类细胞进行交流。SLs就是这样一个分子家族——人类细胞和细菌细胞产生相同的分子是非常不寻常的，这表明它们之间存在某种进化联系。此外，据计算，我们的肠道中每时每刻都有几克的SLs，它们对我们的健康起着至关重要的作用。最近的研究将微生物群与糖尿病、肥胖和癌症等疾病联系起来。所有的细胞都是通过一个多步骤的途径来制造SLs的，这些步骤都是由一种叫做酶的分子机器催化（加速）的。研究主要集中在参与人类SL生物合成的酶上，但对微生物群中的SL生物合成知之甚少。为了充分了解我们和细菌之间的关系，我们必须了解细菌是如何制造和运输这些复杂分子的，以及我们是如何代谢它们的。我们将与来自美国和德国的世界专家以及来自英国的合作伙伴一起研究肠道和口腔细菌如何制造SLs。我们将从丝氨酸棕榈酰基转移酶（SPT）的研究开始，SPT使用两个主要组成部分——一种叫做l -丝氨酸的氨基酸和一种长链脂肪酸，来制造第一个SL中间体。我们将确定每种细菌中SPT的三维结构，并比较它们的形状和演化。特别有趣的是，细菌SLs的结构是不寻常的，包含独特的化学指纹，我们将通过给细菌喂食所提出的构建块的重版本并跟踪它们的结合来研究它们的起源。对于微生物群如何制造不寻常的支链氨基酸，我们一无所知，因此我们将研究将支链氨基酸转化为特定构建块的酶。细菌含有神经酰胺和一种不寻常的肌醇糖，所以我们将纯化和表征肌醇磷酸合成酶（MIPS），它使用葡萄糖磷酸作为底物。在我们的研究结束时，我们将开始定义微生物群的生物合成蓝图。我们的研究结果将引起学术微生物学家和化学家以及对人类健康感兴趣的人的兴趣。此外，许多制药和医疗保健公司也对微生物组感兴趣，他们可以利用我们的知识开发可能对疾病和长期健康产生影响的疗法。

Animal and bacterial cells have a protective, water-resistant outer shell that is composed of molecules with a water-loving (hydrophilic) head group and a long, water-hating (hydrophobic) tail. This large family of molecules are called lipids and include common things like saturated/unsaturated fats and cholesterol. One particular sub-family of lipids is called sphingolipids (SLs) and their more complex ceramide versions (which have two fatty tails). The SLs not only play structural roles in the outer shell that allow the cell membrane to resist water and let nutrients in and waste out; they are also able to stimulate the human immune system. SL levels are dynamic but also tightly controlled - any increase or decrease in the cellular SL levels is a sign that something has gone wrong. Changes in SL levels are strongly linked with old age and diseases such as Alzheimer's, diabetes, asthma, cancer and nerve-wasting diseases. An exciting area of research with direct implications for human health is the discovery that humans are hosts for many different types of bacteria - collectively these are known as the microbiota/microbiome. Current estimates are that for every human cell in our body, there is a bacterial one. These bacteria can be "bad" and cause disease (e.g. superbugs) but most are "good" bacteria and are beneficial to our well being. These bacteria live in our mouths, on our skin and in our gut and help us metabolise our food and are also thought to play protective roles. A surprising discovery was that the bacteria that live with us produce molecules that allow bacterial and human cells to communicate. One such family of molecules are the SLs - it is highly unusual that human and bacterial cells both make the same molecule and this suggests some sort of evolutionary link. Moreover, it has been calculated that we have several grams of SLs in our gut at any one time and they are making a vital contribution to our health. Recent studies have linked the microbiota to diseases such as diabetes, obesity and cancer.All cells make SLs by a multi-step pathway using simple building blocks - the steps are catalysed (sped up) by molecular machines called enzymes. Research has focussed on the enzymes involved in human SL biosynthesis but very little is known about SL biosynthesis in the microbiota. To fully understand the relationship between us and bacteria we must learn how bacteria make and transport such complex molecules as well as understanding how we metabolise them. We will study how gut and mouth bacteria make SLs with world experts in America and Germany with a collaborator from the UK. We will begin with a study of the enzyme serine palmitoyltransferase (SPT) that uses two main building blocks - an amino acid called L-serine and a long chain fatty acid, to make the first SL intermediate. We will determine the 3D structure of the SPT in each bacterium and compare their shapes and evolution. Of special interest, the structure of the bacterial SLs is unusual and contains distinctive chemical fingerprints and we will investigate their origins by feeding the bacteria heavy versions of the proposed building blocks and tracking their incorporation. Nothing is known about how the microbiota makes unusual branched chain SLs so we will study enzymes that convert can branch-chain amino acids into specific building blocks. Bacteria contain ceramides with an unsusual inositol sugar so we will purify and characterise the enzyme myo-inositol phosphate synthase (MIPS) that uses glucose phosphate as a substrate. At the end of our study we will have begun to define the biosynthetic blueprint of the microbiota. Our results will be of interest to academic microbiologists and chemists as well as those interested in human health. Moreover, a number of drug and healthcare companies are also interested in the microbiome and they could use our knowledge to develop therapies that may have impact on disease and long term well being.