Sulfolipid Head Group Biosynthesis in Photosynthetic Organisms

光合生物中的硫脂头基生物合成

• 批准号: 9807943
• 负责人: Christoph Benning
• 金额: $ 24万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-09-01 至 2001-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9807943&HistoricalAwards=false
• 关键词: Sulfolipid; Head; Group; Biosynthesis; Photosynthetic

9807943Benning The abundant non-phosphorous sulfolipid sulfoquinovosyl diacylglycerol is specifically associated with photosynthetic membranes of bacteria and plants. The unique head group consists of a 6-sulfonate derivative of glucose called sulfoquinovose. Three major pathways contribute to the biosynthesis of sulfolipid: carbohydrate metabolism, sulfur assimilation, and fatty acid biosynthesis. There is good evidence for the final assembly of the sulfolipid by the transfer of the sulfoquinovosyl moiety from UDP-sulfoquinovose to the sn-3 position of diacylglycerol. However, very little is still known about the biosynthesis of the precursor UDP-sulfoquinovose and the mechanism for the introduction of the sulfonate group. It is the objective of this project, to elucidate the biosynthesis of UDP-sulfoquinovose, thereby determining the pathway of sulfolipid biosynthesis and possibly discovering a novel biochemical reaction crucial to the synthesis of sulfonates in biological systems. One approach is to characterize the proteins encoded by the sqdB sulfolipid genes of photosynthetic bacteria or by the orthologous SQD1 plant gene, and to elucidate the metabolic reaction catalyzed. These proteins are proposed to be involved in the biosynthesis of UDP-sulfoquinovose from UDP-glucose, because their amino acid sequence is similar to those of sugar nucleotide modifying enzymes. Recombinant SQDB or SQD1 proteins convert UDP-glucose to a new compound in vitro. The structural elucidation of this compound, presumably the sulfur acceptor for the formation of UDP-sulfoquinovose, is expected to provide clues to the reaction catalyzed by the SQDB or SQD1 proteins in vivo. A second approach is aimed at the identification of the possible sulfur donor for UDP-sulfoquinovose biosynthesis and, thus, the branch point between general sulfur metabolism and sulfolipid biosynthesis. For this purpose, four mutants of the cyanobacterium Synechocystis sp. PCC6803 deficient in different steps of sulfate assimilation and reduction will be constructed by targeted gene disruption and will be tested for their capability to synthesize sulfolipid. Sulfolipid is a constituent of photosynthetic membranes of bacteria and plants. The head group of the sulfolipid is unique, consisting of a sulfonic acid derivative of glucose called sulfoquinovose. It is the objective of this project to elucidate the crucial biochemical reaction(s) leading to the biosynthesis of this naturally occurring sulfonic acid. The genes encoding the enzyme thought to catalyze the biosynthesis of the head group are available from bacteria and plants. These genes are used to produce recombinant proteins in E. coli that can be studied in detail to elucidate the reaction mechanism. To address the question for the origin of the sulfur in sulfolipid, genes known to encode proteins involved in different reactions of the general sulfur metabolism in cyanobacteria will be inactivated. The resulting mutants will be tested for their competence for sulfolipid biosynthesis. The newly acquired knowledge about the biosynthesis of the sulfolipid head group will not only solve the pathway of sulfolipid biosynthesis, but may also provide clues towards the production of sulfonic acids by genetic engineering. It has been demonstrated in different laboratory tests that sulfolipid has anti-viral and anti-tumor activities. Thus, it may become desirable to produce large quantities of this compound in an inexpensive way in the near future.

9807943 Benning丰富的非磷硫脂磺基喹诺糖基二酰基甘油与细菌和植物的光合膜特异性相关。独特的头基由葡萄糖的6-磺酸盐衍生物组成，称为磺基喹诺糖。硫脂的生物合成有三条主要途径：碳水化合物代谢、硫同化和脂肪酸生物合成。有充分的证据表明，磺基喹诺糖基部分从UDP-磺基喹诺糖转移到甘油二酯的sn-3位，最终组装成磺基脂质。然而，关于前体UDP-磺基喹诺糖的生物合成和引入磺酸基的机制仍然知之甚少。本项目的目的是阐明UDP-磺基喹诺糖的生物合成，从而确定硫脂生物合成的途径，并可能发现生物系统中磺酸盐合成的新的生物化学反应。一种方法是表征由光合细菌的sqdB硫脂基因或由orthophosphorus SQD 1植物基因编码的蛋白质，并阐明催化的代谢反应。这些蛋白质被认为参与从UDP-葡萄糖合成UDP-磺基喹诺糖，因为它们的氨基酸序列与糖核苷酸修饰酶的氨基酸序列相似。重组SQDB或SQD 1蛋白在体外将UDP-葡萄糖转化为新化合物。该化合物的结构解析，推测为UDP-磺基喹诺糖形成的硫受体，预期将为SQDB或SQD 1蛋白在体内催化的反应提供线索。第二种方法旨在鉴定UDP-磺基喹诺糖生物合成的可能的硫供体，从而鉴定一般硫代谢和硫脂生物合成之间的分支点。为此目的，四个突变体的蓝细菌集胞藻种PCC 6803缺乏硫酸盐同化和还原的不同步骤，将构建有针对性的基因破坏，并将测试其合成硫脂的能力。 硫脂是细菌和植物光合作用膜的组成部分。硫脂质的头部基团是独特的，由称为磺基喹诺糖的葡萄糖的磺酸衍生物组成。本项目的目的是阐明导致这种天然存在的磺酸生物合成的关键生物化学反应。编码被认为催化头基生物合成的酶的基因可从细菌和植物中获得。这些基因用于在大肠杆菌中产生重组蛋白。可以详细研究以阐明反应机制。为了解决硫脂中硫的来源问题，将灭活已知编码参与蓝藻中一般硫代谢的不同反应的蛋白质的基因。将测试所得突变体的硫脂生物合成能力。关于硫脂头部基团的生物合成的新知识不仅将解决硫脂生物合成的途径，而且还可能为通过基因工程生产磺酸提供线索。在不同的实验室试验中已经证明，硫脂具有抗病毒和抗肿瘤活性。因此，在不久的将来以廉价的方式生产大量的这种化合物可能变得合乎需要。