Regulation of Tetrapyrrole Synthesis in Rhodobacter capsulatus

光合细菌使用单一分支途径合成所有四种四吡咯终产物：血红素、细菌叶绿素、维生素 B-12 和西罗血红素。 这条分支途径之所以如此有趣，是因为这四种产物在细胞代谢中发挥着如此不同的作用，并且需要的量也截然不同。 这项研究的最终目的是了解光合细菌荚膜红杆菌如何协调四种四吡咯产物的合成。 最近的证据表明，PufQ 蛋白与某些四吡咯中间体结合，并参与其向细菌叶绿素的转化。 因此，细菌叶绿素的合成受细胞中存在的 PufQ 蛋白量的调节。 载体蛋白（例如 PufQ）在调节导致血红素和细菌叶绿素的常见四吡咯途径中的作用正在确定。 当粪卟啉从荚膜 R. capsulatus 中分泌出来时，它会与 32kDa 的蛋白质复合，该蛋白质太大而无法成为 PufQ。 该蛋白质正在被部分测序，使用寡核苷酸探针克隆基因，并构建缺乏该蛋白质的突变体。 该突变体的表型可以确定该蛋白质是否是血红素合成、细菌叶绿素合成或两者都需要的。 其他hem突变体正在被分离，以便可以确定哪种四吡咯中间体是第一个结合载体蛋白的。 可以说，导致叶绿素和血红素等四吡咯类化合物产生的生物合成途径是自然界最重要的途径之一。 目前，人们对这一复杂途径的调控机制知之甚少。 光合细菌荚膜红杆菌提供了一个理想的模型系统，因为它合成所有四种四吡咯最终产物，并且适合于遗传和生物化学研究。 本研究旨在了解如何确保这些化合物的充足且平衡的供应。 //

Photosynthetic bacteria use a single branched pathway to synthesize all four tetrapyrrole endproducts: heme, bacteriochlorophyll, vitamin B-12, and siroheme. What makes this branched pathway so interesting is that the four products play such diverse roles in cellular metabolism and are required in vastly different amounts. The ultimate aim of this research is to understand how the photosynthetic bacterium Rhodobacter capsulatus coordinates the synthesis of the four tetrapyrrole products. Recent evidence suggests that the PufQ protein binds to some tetrapyrrole intermediate and is involved in its conversion to bacteriochlorophyll. Synthesis of bacteriochlorophyll is therefore regulated by the amount of PufQ protein present in the cell. The role of carrier proteins such as PufQ in the regulation of the common tetrapyrrole pathway that leads to heme and bacteriochlorophyll is being determined. When coproporphyrin is excreted from R. capsulatus it is complexed with a 32kDa protein which is too large to be PufQ. This protein is being partially sequenced, the gene cloned using oligonucleotide probes, and a mutant constructed that lacks the protein. The phenotype of this mutant allows for a determination of whether this protein is required for heme synthesis, bacteriochlorophyll synthesis, or both. Other hem mutants are being isolated so that it can be determined which tetrapyrrole intermediate is the first to bind a carrier protein. It can be argued that the biosynthetic pathway leading to the production of tetrapyrroles such as chlorophyll and heme is one of the most important pathways in nature. Currently, very little is known about how this complex pathway is regulated. The photosynthetic bacterium Rhodobacter capsulatus provides an ideal model system, in that it synthesizes all four tetrapyrrole endproducts and is amenable to study both genetically and biochemically. This research aims at an understanding of how an adequate yet balanced supply of these compounds is ensured. //