Heme Biosynthesis in Bradyrhizobium japonicum

日本慢生根瘤菌中血红素的生物合成

• 批准号: 0077628
• 负责人: Mark O'Brian
• 金额: $ 37.5万
• 依托单位: SUNY at Buffalo
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-08-01 至 2004-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0077628&HistoricalAwards=false
• 关键词: Heme; Biosynthesis; Bradyrhizobium; japonicum

The long-term aim of this project is to understand the regulation of heme biosynthesis in the symbiotic nitrogen-fixing bacterium Bradyrhizobium japonicum. The iron-containing porphyrin ring (heme) is involved in several enzymatic reactions requiring microanaerobic conditions necessary for efficient nitrogen fixation (free-living or symbiotic). The multienzyme pathway for heme formation ends with the insertion of iron into the protoporphyrin ring in a reaction catalyzed by ferrochelatase. Because iron may be a limiting nutrient and porphyrins are cytotoxic, this suggests the need for coordination of heme biosynthesis with iron availability. A novel protein called Irr has been recently identified and proposed to mediate iron control of heme biosynthesis. Irr is present under iron limitation and negatively regulates the heme biosynthesis gene hemB, preventing protoporphyrin accumulation from exceeding iron availability. Irr is a conditionally stable protein that degrades rapidly when cells are exposed to iron. Heme is an effector molecule in this iron-mediated degradation, binding to a specific motif in Irr. Irr also binds ferrochelatase directly. This proposal will test the hypothesis that Irr mediates iron control of the heme pathway by responding to the status of protoporphyrin and heme at the site of heme synthesis. The role of heme in mediating iron-dependent Irr degradation will be elucidated. Specifically, two plausible mechanisms will be tested: heme catalysis of Irr oxidation leading to degradation, or heme-induced conformational change in Irr, rendering it accessible to proteases. The binding of ferrochelatase to Irr and the effect of this binding on Irr activity will also be studied. This work focuses on a metabolic pathway that is important for energy production and its novel regulation by bacterial cells, and thus should provide insights on the ability of bacteria to adjust to diverse environmental conditions. The environmental adaptability of Bradyrhizobium japonicum is of special interest because this bacterium establishes a nitrogen-fixing symbiotic association with soybeans. Because this relationship is beneficial to a commercially important plant crop, B. japonicum is thus of economic and agricultural interest. These studies will also involve the training of graduate and undergraduate students, including women and underrepresented minority trainees.

本项目的长期目标是了解共生固氮菌日本慢生根瘤菌（Bradyrhizobium japonicum）中血红素生物合成的调控。 含铁卟啉环（血红素）参与了几种酶促反应，需要有效固氮（自由生活或共生）所必需的微厌氧条件。 血红素形成的多酶途径在亚铁螯合酶催化的反应中以铁插入原卟啉环结束。 由于铁可能是一种限制性营养素，而卟啉具有细胞毒性，这表明需要协调血红素生物合成与铁的可用性。 一种新的蛋白质称为Irr最近已被确定，并提出调解血红素生物合成的铁控制。 Irr在铁限制下存在并负调节血红素生物合成基因hemB，防止原卟啉积累超过铁可用性。 Irr是一种条件稳定的蛋白质，当细胞暴露于铁时会迅速降解。 血红素是这种铁介导的降解中的效应分子，与Irr中的特定基序结合。 Irr也直接结合亚铁螯合酶。该提案将测试的假设，Irr介导的血红素途径的铁控制，通过响应原卟啉和血红素在血红素合成的网站的状态。 血红素在介导铁依赖性Irr降解中的作用将得到阐明。 具体而言，两个合理的机制将进行测试：血红素催化Irr氧化导致降解，或血红素诱导的构象变化，Irr，使其接近蛋白酶。 还将研究铁螯合酶与Irr的结合以及这种结合对Irr活性的影响。 这项工作的重点是代谢途径，这是重要的能源生产和其新的调控细菌细胞，因此应该提供洞察细菌的能力，以适应不同的环境条件。日本慢生根瘤菌的环境适应性特别令人感兴趣，因为这种细菌与大豆建立了固氮共生关系。因为这种关系对商业上重要的植物作物B是有益的。因此，日本根瘤菌具有经济和农业利益。这些研究还将涉及培训研究生和本科生，包括妇女和代表性不足的少数民族受训人员。