The mechanistic enzymology of thiamin biosynthesis

硫胺素是人类饮食的重要组成部分，每日推荐摄入量为1.2毫克。它也是一种重要的商业化学品，被广泛用作食品添加剂和调味剂。化学合成的年产量约为3300吨。硫胺素依赖性酶在碳水化合物和支链氨基酸代谢中起重要作用。目前，我们对这类酶的机理理解是复杂的。相比之下，虽然硫胺素是第一个被发现的维生素，但我们对其生物合成的理解仍然不完整，因为生物合成途径非常复杂，涉及前所未有的反应化学。我们研究的长期目标是全面了解所有生命形式中硫胺素生物合成、回收和分解代谢的酶学机制，并阐明硫胺素代谢与细胞生理学其他方面之间的联系。在下一个资助期，我们将描述旨在阐明细菌和真核生物中硫胺素、噻唑和嘧啶的生物合成的研究。这些杂环形成反应涉及新的生物化学。我们的策略是结合动力学，改良底物，蛋白质

Thiamin is an essential component of the human diet with an RDA of 1.2 mg. It is also an important commercial chemical and it is widely used as a food additive and flavoring agent. Annual production, by chemical synthesis, is on the order of 3,300 tons. Thiamin-dependent enzymes play an important role in carbohydrate and branched-chain amino acid metabolism. At this time, our mechanistic understanding of this class of enzymes is sophisticated. In contrast, while thiamin was the first vitamin identified, our understanding of its biosynthesis is still incomplete because the biosynthetic pathway is complex and involves unprecedented reaction chemistry. The long-term goal of our research is the complete mechanistic understanding of the enzymology of thiamin biosynthesis, salvage and catabolism, in all forms of life and the elucidation of connections between thiamin metabolism and other aspects of cellular physiology. In the next grant period, we describe studies designed to elucidate the biosynthesis of the thiamin thiazole and pyrimidine in both bacteria and eukaryotes. These heterocycle forming reactions involve novel biological chemistry. Our strategy will involve a combination of kinetics, modified substrates, protein mutagenesis and structural studies. We will also identify the genes involved in thiamin breakdown and salvage. Bacteria, in the human digestive tract, containing these genes are likely to play an important role in controlling the human thiamin RDA. Finally, we will explore the use of 18F-thiamin as a PET imaging agent, ultimately to determine the global thiamin distrubution in healthy and diseased humans. RELEVANCE (See instructions): Thiamin (vitamin B1) is essential for all forms of life. Our studies will facilitate the commercial production of thiamin by fermentation and have potential applications in the design of new antibiotics. Understanding thiamin catabolism and salvage will enable us to evaluate the importance of these activities in the human digestive tract. 18F-thiamin has potential use, as an imaging agent, in basic human biology and in tumor detection.