Thiamin Metabolism in Plants: Elucidation of the 4-Methyl-5-(b-hydroxyethyl)Thiazole Phosphate (HET) Biosynthetic Pathway in Arabidopsis

植物中的硫胺素代谢：拟南芥中 4-甲基-5-(b-羟乙基)噻唑磷酸酯 (HET) 生物合成途径的阐明

• 批准号: 0236210
• 负责人: David Shintani
• 金额: $ 37.5万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-05-01 至 2006-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0236210&HistoricalAwards=false
• 关键词: Thiamin; Metabolism; Plants; Elucidation; Methyl

Thiamin pyrophosphate (TPP), which is formed through the condensation of two major intermediates, 4-methyl-5-(b-hydroxyethyl)thiazole phosphate (HET) and 2-methyl-4-amino-5-hydroxymethylpyrimidine pyrophosphate (HMP), is an essential enzyme co-factor required for the viability of all organisms. While TPP is only synthesized by bacteria, fungi and photosynthetic organisms, animals and humans must derive TPP from dietary sources of thiamin. Although plants represent a major source of dietary thiamin, surprisingly little is understood about most aspects of its synthesis in plants. This is particularly true for the HET intermediate of TPP. Most of what is known about HET biosynthesis has been derived from genetic and biochemical studies in microorganisms where this compound is derived from different synthetic precursors using different enzymatic machinery. Although a previous study suggested that HET is synthesized as described for E. coli, where deoxy-xylulose-5-phosphate (DXP) is a precursor, the Shintani lab has performed studies showing that plants can synthesize HET in the absence of DXP. This result suggests that plants may possess an alternative pathway to HET that exists in place of or in addition to the previously described "E. coli-like" pathway. The overall goal of this research is to use a combination of molecular and biochemical approaches to determine the biosynthetic pathway(s) leading to formation of HET in plants. To achieve this goal the following research objectives will be performed: 1) Determine the biosynthetic precursors leading to thiamin biosynthesis in plants, 2) Determine the role of the plant orthologue of the yeast Thi4 protein in HET biosynthesis, 3) Identify and functionally analyze additional Arabidopsis HET biosynthetic genes. Thiamin (Vitamin B1) deficiencies in humans can lead to a condition known as Beriberi that is manifested by severe neurological disorders and a general wasting phenomenon. This disease is primarily associated with poverty-stricken populations of developing countries whose diets subsist primarily of polished grain products such as polished rice or bleached wheat flour. A sustainable solution to thiamin deficiencies in humans would be to increase the nutritional content of staple food crops that endogenous populations of the world commonly consume. By genetic engineering such crops for increased thiamin, it should be possible to positively impact the nutritional needs of the global population. Unfortunately, the major impediment to such an effort is a current lack of knowledge pertaining to the biosynthesis of thiamin in plants. The increased biosynthetic knowledge obtained through these studies will be important for the rational design of crops engineered for elevated thiamin levels for improved human and animal nutrition.

硫胺素焦磷酸盐（TPP）是由两种主要中间体4-甲基-5-（b-羟乙基）噻唑磷酸盐（HET）和2-甲基-4-氨基-5-羟甲基嘧啶焦磷酸盐（HMP）缩合而成，是所有生物体生存所必需的酶辅因子。虽然TPP仅由细菌、真菌和光合生物合成，但动物和人类必须从硫胺素的饮食来源中获得TPP。虽然植物代表了膳食硫胺素的主要来源，但令人惊讶的是，对其在植物中合成的大多数方面知之甚少。这对于TPP的HET中间体尤其如此。大多数关于HET生物合成的已知信息来源于微生物中的遗传和生物化学研究，其中该化合物来源于使用不同酶机制的不同合成前体。尽管先前的研究表明HET是如E.大肠杆菌中，其中脱氧木酮糖-5-磷酸（DXP）是前体，Shintani实验室已经进行了研究，表明植物可以在没有DXP的情况下合成HET。这一结果表明，植物可能具有替代途径，以HET存在的地方或除了先前描述的“E。大肠杆菌样”途径。本研究的总体目标是使用分子和生物化学方法的组合来确定导致植物中HET形成的生物合成途径。为了实现这一目标，将进行以下研究目标：1）确定导致植物中硫胺素生物合成的生物合成前体，2）确定酵母Thi 4蛋白的植物直向同源物在HET生物合成中的作用，3）鉴定和功能分析另外的拟南芥HET生物合成基因。人体缺乏硫胺素（维生素B1）会导致一种被称为脚气病的疾病，表现为严重的神经系统疾病和一般的消耗现象。这种疾病主要与发展中国家的贫困人口有关，他们的饮食主要是精米或漂白小麦粉等精加工谷物产品。解决人类维生素B1缺乏症的可持续办法是增加世界本地人口通常消费的主食作物的营养成分。通过对此类作物进行基因工程以增加硫胺素，应该可以对全球人口的营养需求产生积极影响。不幸的是，这种努力的主要障碍是目前缺乏有关植物中硫胺素生物合成的知识。通过这些研究获得的更多的生物合成知识对于合理设计提高硫胺素水平以改善人类和动物营养的作物将是重要的。