Microbial metabolism of aliphatic alkenes & epoxides

描述(由申请人提供)：本提案的目标是调查短链碳氢化合物代谢的微生物途径以及与这些途径相关的酶、辅因子和调节元件的特性。虽然碳氢化合物的活化本身是有趣的，也许更有趣的是对人类健康具有更广泛影响的是剧毒碳氢化合物氧化产物的性质和命运。例如，乙烯、丙烯、苯乙烯和异戊二烯(2-甲基丁二烯)等短链烯烃的普遍氧化导致环氧化物的产生，这些环氧化物是高度亲电的烷基化试剂。短链饱和烃的无处不在的氧化包括末端或亚末端的羟基化，分别产生伯醇或仲醇。这些醇的进一步氧化产生有毒的醛(来自伯醇)或酮(来自仲醇)。环氧化物、醛和酮也可作为其他代谢途径和工业过程的中间体或最终产物。尽管这些化合物有毒性，但一些细菌能够直接或间接地利用脂肪族环氧化物、醛和酮作为碳源和能源(即通过形成它们作为碳氢化合物分解代谢的中间体)而生长。我们实验室的工作揭示了细菌环氧化物和酮代谢中涉及的新的转化、辅因子和酶。具体地说，我们发现了脂肪环氧化物和酮代谢的依赖于二氧化碳的途径和酶，其中环氧化物和酮被羧化为β-酮酸，进入中央代谢。尽管这些转化表面上有相似之处，但羧化反应的机理细节是根本不同的。我们打算通过探索这些过程的生化、结构和遗传特征，进一步研究羧化和新型辅因子/酶在细菌碳氢化合物/环氧化物/酮代谢中的核心作用。

DESCRIPTION (provided by applicant): The objectives of this proposal are to investigate microbial pathways of short-chain hydrocarbon metabolism and the properties of the enzymes, cofactors, and regulatory elements associated with these pathways. While hydrocarbon activation is interesting in its own right, perhaps even more interesting, and with broader implications for human health, are the nature and fate of highly toxic hydrocarbon oxidation products. For example, the ubiquitous oxidation of short-chain alkenes such as ethylene, propylene, styrene and isoprene (2-methybutadiene) results in the production of epoxides, which are highly electrophilic alkylating agents. The ubiquitous oxidation of short-chain saturated hydrocarbons involves either terminal or subterminal hydroxylation to produce primary or secondary alcohols, respectively. The further oxidation of these alcohols produces toxic aldehydes (from primary alcohols) or ketones (from secondary alcohols). Epoxides, aldehydes and ketones are also produced as intermediates or end-products of other metabolic pathways and by industrial processes. In spite of the toxicity of these compounds, a number of bacteria are able to grow using aliphatic epoxides, aldehydes and ketones as carbon and energy sources, either directly or indirectly (i.e. by forming them as intermediates of hydrocarbon catabolism). Work in our laboratory has revealed that novel transformations, cofactors and enzymes are involved in bacterial epoxide and ketone metabolism. Specifically, we discovered CO2-dependent pathways and enzymes for aliphatic epoxide and ketone metabolism, wherein epoxides and ketones are carboxylated to beta-keto acids for entry to central metabolism. In spite of the superficial similarities of these transformations, the mechanistic details of the carboxylation reactions are fundamentally different. We intend to further our work on the central roles of carboxylation and novel cofactors/enzymes in bacterial hydrocarbon/epoxide/ketone metabolism by pursuing the biochemical, structural, and genetic characterization of these processes.