Novel Catalases and their Products

描述(申请人提供)：本申请的长期目标是阐明一组在序列和结构上与过氧化氢酶相关的新蛋白质的作用，并确定其反应和新产品的生化和化学。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。人们可以预料到这些新的过氧化氢酶与潜在的氧化代谢和/或在天然过氧化氢的处置中起作用的选择性反应。这一建议的原型酶是丙二烯氧化物合成酶，这种酶催化细胞色素P450类型的反应，但显示出与过氧化氢酶明显的序列同源性。在目标1中，将利用新获得的与过氧化氢酶相关的AOS的X射线晶体结构来揭示催化的机理基础，并与人类过氧化氢酶进行比较。目的是了解在过氧化氢酶折叠中催化P450-型化学的能力。目的2将重点分析其他新的候选酶的催化活性，这些候选酶具有类似的序列特征，即对于~40kD的过氧化氢酶来说，在异常短的多肽中保留了过氧化氢酶的血红素结合特征。这些酶存在于生物体中，包括具有致病性的重要细菌和一种被描述为对世界粮食供应构成主要威胁的作物枯萎病菌。丙二烯氧化物在生物技术中具有重要的作用，它们的环戊酮衍生物也因其强大的抗肿瘤作用而受到研究。目标3将寻求确定天然丙二烯氧化物的结构和精确的立体化学，特别是与其环化有关的结构问题。这对于理解氧化丙烯合成酶反应的性质以及环戊酮的合成化学具有重要意义。这项研究的结果将提供新的见解和新的思维方式来研究一个被长期认可的蛋白质家族的酶功能，该家族被确立为氧化防御前沿的哨兵。

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.