Novel Catalases and their Products

描述（由申请人提供）：本申请的长期目标是阐明在序列和结构上与过氧化氢酶相关的一组新蛋白质的作用，并定义其反应和新产物的生物化学和化学。过氧化氢酶因其在所有需氧生物的氧化防御中的关键作用而闻名。人们可以预测这些新的过氧化氢酶亲戚与潜在的氧化代谢和/或在处理天然过氧化物中起作用的选择性反应。该提议的原型酶是一种氧化丙烯合成酶，这种酶催化细胞色素p450型反应，但与过氧化氢酶具有明显的序列同源性。在Aim 1中，新获得的与过氧化氢酶相关的AOS的x射线晶体结构将用于揭示催化的机制基础以及与人类过氧化氢酶的比较和对比。目标是提供对过氧化氢酶折叠中催化p450型化学的能力的理解。Aim 2将重点分析其他具有相似序列特征的新型候选酶的催化活性，这些特征被定义为过氧化氢酶在异常短的过氧化氢酶多肽中保留血红素结合特征，仅为~40kD。这些酶存在于生物体中，包括具有重要致病性的细菌和被认为对世界粮食供应构成主要威胁的作物枯萎菌。烯氧化物在生物技术中具有重要意义，其环戊烯酮衍生物也因其有效的抗肿瘤作用而被研究。目标3将寻求建立天然烯氧化物的结构和精确立体化学，特别是与它们的环化有关的结构问题。这对理解氧化烯合酶反应的性质以及环戊酮合成的化学性质具有重要意义。这项研究的结果将提供新的见解和新的方式来思考一个长期公认的蛋白质家族的酶促能力，并在氧化防御的前沿确立了哨兵的角色。

DESCRIPTION (provided by applicant): The long-term objective of this application is to elucidate the roles of a novel group of proteins related in sequence and structure to catalase and to define the biochemistry and chemistry of their reactions and novel products. Catalase is renowned for its key role in the oxidative defense of all aerobic organisms. One can anticipate selective reactions of these new catalase relatives with potential oxidative metabolism and/or functioning in the disposition of natural peroxides. The prototypical enzyme of this proposal is an allene oxide synthase, an enzyme that catalyzes a cytochrome P450-type of reaction yet which exhibits distinct sequence homology to catalase. In Aim 1, a newly available X-ray crystal structure of the catalase-related AOS will be used to reveal the mechanistic basis of catalysis and the comparisons and contrasts with human catalase. The goal is to provide an understanding of the ability to catalyze P450-type chemistry within the catalase fold. Aim 2 will focus on analysis of the catalytic activities of other novel enzyme candidates that have similar sequence characteristics defined as retention of the heme-binding features of a catalase within an unusually short polypeptide for catalases of only ~40kD. These enzymes occur in organisms that include bacteria of importance for their pathogenicity and a crop blight fungus characterized as a major threat to the world's food supply. Allene oxides are of major importance in biotechnology and their cyclopentenone derivatives are also studied for their potent antineoplastic effects. Aim 3 will seek to establish the structure and precise stereochemistry of natural allene oxides and especially structural issues pertinent to their cyclizations. This is of fundamental interest in understanding the nature of allene oxide synthase reactions as well as the chemistry of cyclopentenone synthesis. The results of this study will provide new insights and a new way of thinking about the enzymatic capabilities of a long-recognized protein family with established roles as a sentinel at the forefront of oxidative defense.