Novel tetrapyrrole biosynthetic routes in prokaryotes: Structure and function of enzymes for the biosynthesis of heme d1 in denitrifying bacteria and heme in archaea

原核生物中新的四吡咯生物合成途径：反硝化细菌中血红素 d1 和古细菌中血红素生物合成酶的结构和功能

• 批准号: 232172969
• 负责人: Professorin Dr. Gunhild Monika Layer
• 金额: --
• 依托单位: Lehrstuhl für Pharmazeutische Biologie und Biotechnologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/232172969?language=en
• 关键词: Novel; tetrapyrrole; biosynthetic; routes; prokaryotes

Cyclic tetrapyrroles such as heme and chlorophyll fulfil important biological functions and are involved in processes like aerobic and anaerobic respiration or photosynthesis. Heme d1 is another cyclic tetrapyrrole, which is important for bacterial denitrification and thus for the global nitrogen cycle. The biosynthesis pathways of heme in sulfate-reducing bacteria and archaea and of heme d1 in denitrifying bacteria are related and were elucidated only recently. One reaction occurring in both pathways is the decarboxylation of two acetate groups of siroheme to the corresponding methyl groups of didecarboxysiroheme catalyzed by the enzyme siroheme decarboxylase. The Radical SAM enzyme AhbD catalyzes the last reaction of the siroheme-dependent biosynthesis route to heme, namely the oxidative decarboxylation of two propionate groups of the intermediate iron-coproporphyrin III yielding the two vinyl groups of heme. Within this project, the catalytic mechanisms of the siroheme decarboxylase and of the heme synthase AhbD will be investigated. In the case of siroheme decarboxylase, there are different isoforms of the enzyme that catalyze either only one or both of the two decarboxylation reactions. Therefore, one aim of this project is to identify the respective amino acid residues, which are involved in substrate binding and catalysis, and to identify the determinants responsible for the substrate and reaction specificity of the different siroheme decarboxylase isoforms. Concerning AhbD, the product of the decarboxylation event will be identified and the radical mechanism of the enzyme will be studied by EPR spectroscopy. Another aim is the determination of the three-dimensional structure of AhbD in particular in complex with its substrate.

像血红素和叶绿素这样的环状四氢化合物具有重要的生物学功能，并参与有氧和无氧呼吸或光合作用等过程。血红素D1是另一种环状四吡咯，它对细菌的反硝化作用非常重要，因此对全球氮循环也很重要。硫酸盐还原菌和古生菌中血红素的生物合成途径和反硝化细菌中的血红素D1的生物合成途径是相关的，直到最近才被阐明。在这两个途径中发生的一个反应是，在西罗铁血红素脱羧酶的催化下，两个醋酸基的西洛铁血红素脱羧基为相应的二脱羧基西罗西铁的甲基。自由基SAM酶ahbd催化依赖于铁血红素的生物合成路线的最后一步反应，即中间体铁-共比例卟啉III的两个丙酸基的氧化脱羧基，生成两个血红素的乙烯基。在这个项目中，将研究siroheme脱羧酶和heme合成酶ahbd的催化机制。在铁血红素脱羧酶的情况下，有不同的酶亚型，只催化两个脱羧基反应中的一个或两个。因此，本项目的目的之一是确定参与底物结合和催化的各个氨基酸残基，并确定决定底物和不同含铁血红素脱羧酶亚型反应专一性的决定因素。对于AHBD，将通过EPR谱鉴定脱羧基事件的产物，并研究该酶的自由基机制。另一个目标是确定AHBD的三维结构，特别是与其底物形成的络合物。