Aflatoxin Biosynthesis and Iterative Type I Polyketide Synthases

黄曲霉毒素生物合成和迭代 I 型聚酮化合物合成酶

• 批准号: 7561699
• 负责人: CRAIG ARTHUR TOWNSEND
• 金额: $ 41.92万
• 依托单位: JOHNS HOPKINS UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1978
• 资助国家: 美国
• 起止时间: 1978-02-01 至 2013-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7561699
• 关键词: Accounting; Active Sites; Acyl Carrier Protein; Aflatoxins; Africa; Anabolism; Asia; Aspergillus; Biochemical; Biological Factors; Cancer Etiology; Catalysis; Cell Cycle; Central America; Cereals; Cessation of life; Chemicals; Chemistry; Chronic; Complex; Cyclization; Cytochrome P450; DNA; DNA Sequence Rearrangement; Data; Disease; Environmental Carcinogens; Enzymes; Epidemiology; Food; Goals; Grant; Hepatitis; Hot Spot; Incidence; Infection; Ingestion; Lead; Length; Link; Mutation; Mycotoxins; Names; Oxidation-Reduction; Principal Investigator; Process; Proteins; Reaction; Recruitment Activity; Research; Risk Factors; Roentgen Rays; Role; Study models; System; TP53 gene; Toxin; Transacylase; Type I Polyketide Synthase; Work; environmental toxicology; forging; human disease; mimetics; molecular rearrangement; polyketide synthase; preference; premature; programs; public health relevance; research study

DESCRIPTION (provided by applicant): The aflatoxins are a paradigm among mycotoxins and occupy a central place in environmental toxicology. Hepatocarcinomas are the third most common cause of cancer death in the world. Hepatitis infections and dietary aflatoxin are major risk factors contributing to the incidence of this disease. The aflatoxigenic Aspergillus species, A. parasticus, A. flavus and A. nomius, commonly infect grains and food stuffs where clear epidemiological data correlate to human disease. Chronic ingestion is a major cause of premature death in Asia, Africa and Central America. A direct link has been forged between the interaction of the metabolically activated form of the toxin and DNA, particularly in a hot spot in the p53 gene leading to mutation of its important encoded cell cycle regulating protein. Understanding its biosynthesis will lead to control of this environmental carcinogen. The aflatoxins are created by an unusually long and complex biosynthesis. Key molecular rearrangements, some remarkable mechanistically, are catalyzed by cytochromes P450. The mechanisms of these cleavage and rearrangement reactions will be studied and modeled by chemical mimetics to understand their underlying chemistry. The second, and principal, goal is to capitalize upon exciting progress made in the current grant period to understand the function of non-reducing iterative polyketide synthases central to aflatoxin biosynthesis and many other fungal natural products. Of the three principal types of PKSs, least is known about the programming of iterative Type I systems; that is, how are starter units recruited and synthesis begun, how is chain length determined, how is the canonical and intrinsically reactive poly 2-keto intermediate stabilized, how is redox state controlled during chain elongation, and, finally, how are intramolecular cyclizations controlled to specific ring forms in preference to others. Superimposed on this is the fundamental question of iterative catalysis, a rare but impressively efficient process in which active sites in these polydomainal enzymes are used over and over again, accommodating a sequence of growing substrates yet faithfully executing a synthetic program. We have discovered two previously unrecognized domains in these domains we now believe are general to this class of enzymes, a starter unit:acyl-carrier protein transacylase (SAT) domain, which might account for the classical observation of a starter unit effect, and a product template (PT) domain, which in preliminary results clearly has a role in polyketide stabilization and product templating. Biochemical, X-ray crystallographic and mass spectrometric experiments are outlined to understand the functions of these domains individually and working together in what is already emerging as a new picture of iterative catalysis. PUBLIC HEALTH RELEVANCE The aflatoxins occupy a central place in environmental toxicology. Hepatitis infections and dietary aflatoxin from infected grains and foodstuffs are major risk factors for hepatocarcinoma, the third most common cause of cancer death in the world. Understanding its biosynthesis will lead to its control.

说明(申请人提供)：黄曲霉毒素是真菌毒素中的一个范例，在环境毒理学中占有中心地位。肝癌是世界上癌症死亡的第三大常见原因。肝炎感染和饮食中的黄曲霉毒素是导致这种疾病发生的主要危险因素。产生黄曲霉毒素的曲霉，副曲霉、黄曲霉和诺氏曲霉，通常会感染谷物和食品，在这些地方，明确的流行病学数据与人类疾病相关。在亚洲、非洲和中美洲，长期摄入是过早死亡的主要原因。这种毒素的代谢激活形式与DNA之间的相互作用已经形成了直接的联系，特别是在P53基因的热点区域，导致其重要的编码细胞周期调节蛋白的突变。了解其生物合成将有助于控制这种环境致癌物质。黄曲霉毒素是通过异常漫长和复杂的生物合成而产生的。关键的分子重排，一些值得注意的机械，是由细胞色素P450催化的。这些切割和重排反应的机制将通过化学模拟来研究和建模，以了解它们的基本化学。第二个，也是主要的目标是利用在当前赠款期间取得的令人振奋的进展，以了解黄曲霉毒素生物合成和许多其他真菌天然产物所核心的非还原迭代聚酮合成酶的功能。在三种主要类型的PKS中，人们对迭代类型I系统的编程知之甚少；即，起始单元是如何招募和合成开始的，链长度是如何确定的，正则的和内在活性的聚2-酮中间体是如何稳定的，链延伸过程中氧化还原状态是如何控制的，最后，分子内环化反应是如何控制到特定的环形式而不是其他环形式的。叠加在此之上的是迭代催化的基本问题，这是一种罕见但令人印象深刻的高效过程，在这种过程中，这些多区域酶中的活性位点被反复使用，适应一系列生长的底物，同时忠实地执行合成程序。我们在这些结构域中发现了两个以前未被识别的结构域，我们现在认为它们对这类酶是通用的，一个起始单元：酰基载体蛋白转酰基酶(SAT)结构域，它可能解释了经典的起始单元效应观察，以及一个产物模板(PT)结构域，在初步结果中，它显然在聚酮稳定和产物模板中发挥作用。概述了生化、X射线结晶学和质谱学实验，以了解这些区域的功能，并在已经出现的迭代催化的新图景中共同工作。 与公众健康相关黄曲霉毒素在环境毒理学中占有重要地位。肝炎感染和受感染谷物和食品中的黄曲霉毒素是导致肝癌的主要风险因素，肝癌是世界上第三大常见癌症死亡原因。了解其生物合成将有助于对其进行控制。