Identification of CDP-DAG and serine binding sites in Candida albicans phosphatidylserine synthase, an antifungal drug target

白色念珠菌是人类真菌感染的最常见原因之一。念珠菌引起口腔 感染免疫功能低下的人，如艾滋病患者，它可以导致更严重的 在贫血患者中的侵入性血流感染，例如那些经历癌症化疗的患者， 器官移植虽然有三类抗真菌药治疗侵袭性真菌感染， 耐药性和毒性的组合限制了它们的有效性。因此，需要新的类别， 抗真菌药Cho 1磷脂酰丝氨酸（PS）合酶代表了三个潜在的新药物靶点 原因：1）PS合酶的丧失阻断了毒力，并导致小鼠模型中真菌的清除。 全身或口腔感染。2)PS合酶与哺乳动物（即人）PS脱氢酶不同源，哺乳动物（即人）PS脱氢酶 使用不同的机制来合成PS。哺乳动物PS酶将头部基团从 磷脂酰乙醇胺（PE）或磷脂酰胆碱（PC）用于丝氨酸以制备PS。真菌PS合成酶 将胞苷二磷酸-二酰基甘油（CDP-DAG）和丝氨酸缩合以产生PS。3)真菌PS酶是 PS合成酶抑制剂在所有真菌病原体中都是保守的，因此PS合成酶抑制剂可能是广谱的。的一种方法 开发酶抑制剂的目的是寻找酶的天然底物的竞争性抑制剂。这 通过更全面地了解Cho 1与其 底物：CDP-DAG和丝氨酸。阐明两种底物的结合基序将使我们能够更好地 设计潜在的竞争性抑制剂，例如丝氨酸类似物，作为抗真菌药物的先导化合物 发展CDP-醇磷酸转移酶中常见的CDP-结合共有基序是 [D-（X）2-D-G-（X）2-A-R-（X）8-G-（X）3-D-（X）3-D]，这在Cho 1中发现。然而，丝氨酸结合基序 Cho 1未知使用同源序列比对和计算工具， 原核CDP-醇磷酸转移酶，一个假定的丝氨酸结合基序的解析结构， 鉴定本研究的两个目的是确定CDP-DAG结合基序和发现丝氨酸结合基序。 母题目标1.遗传分析将用于鉴定Cho 1中对底物结合重要的残基。基于 在已知的CDP结合基序上，丙氨酸扫描诱变将用于测试该基序的重要性 在PS合成中。丙氨酸扫描诱变也将用于测试推定的丝氨酸的功能， 结合基序目的2：利用丝氨酸类似物的化学交联来鉴定丝氨酸结合 域在一种偏差较小的生物化学方法中，已经合成了丝氨酸类似物， 用于PS合成的天然L-丝氨酸。这组类似物将被进一步开发并用于交联 底物的PS合成酶，并遵循这与质谱法，以确定氨基酸与它们 互动.然后使用丙氨酸扫描诱变对相互作用的氨基酸进行遗传分析。

Candida albicans is among the most common causes of fungal infections in humans. Candida causes oral infections in immunocompromised people such as those with AIDS, and it can cause even more serious invasive bloodstream infections in neutropenic patients such as those undergoing cancer chemotherapy and organ transplants. Although there are three classes of antifungals to treat invasive fungal infections, a combination of drug resistance and toxicity limit their effectiveness. Thus, there is a need for new classes of antifungals. The Cho1 phosphatidylserine (PS) synthase represents a potential new drug target for three reasons: 1) Loss of PS synthase blocks virulence, and causes clearance of the fungus in mouse models of systemic or oral infection. 2) PS synthase is not homologous to mammalian (i.e. human) PS synthases, which use a different mechanism to synthesize PS. Mammalian PS synthases exchange head groups from phosphatidylethanolamine (PE) or phosphatidylcholine (PC) for serine to make PS. Fungal PS synthase condenses cytidyldiphosphate-diacylglycerol (CDP-DAG) and serine to make PS. 3) Fungal PS synthases are conserved in all fungal pathogens, so PS synthase inhibitors could be broad spectrum. One approach to developing enzyme inhibitors is to look for competitive inhibitors of the enzyme's natural substrates. This approach would be enhanced by a more comprehensive understanding of Cho1's interactions with its substrates: CDP-DAG and serine. Elucidation of the binding motifs for both substrates would allow us to better design potential competitive inhibitors, such as serine analogs, to act as lead compounds for antifungal development. A common CDP-binding consensus motif that is present in CDP-alcohol phosphotransferases is [D-(X)2-D-G-(X)2-A-R-(X)8-G-(X)3-D-(X)3-D], and this is found in Cho1. However, the serine-binding motif for Cho1 is unknown. Using homology sequence alignments and computational tools that superimpose Cho1 on the solved structure of a prokaryotic CDP-alcohol phosphotransferase, a putative serine binding motif was identified. Two aims will be pursued to confirm the CDP-DAG binding motif and discover the serine-binding motif. Aim 1. Genetic analysis will be used to identify residues important for substrate binding in Cho1. Based on the known CDP binding motif, alanine-scanning mutagenesis will be used to test the importance of this motif in PS synthesis. Alanine-scanning mutagenesis will also be used to test the function of the putative serine binding motif. Aim 2: Chemical cross-linking with serine analogs will be used to identify the serine binding domain. In a less-biased biochemical approach, serine analogs have been synthesized that compete with native L-serine for PS synthesis. This set of analogs will be further developed and used to cross-link the substrates to the PS synthase, and follow this with mass spectrometry to identify amino acids with which they interact. Interacting amino acids will then be genetically analyzed using alanine-scanning mutagenesis.