Sinha N, Ferguson S J
Department of Biochemistry, University of Oxford, UK.
FEMS Microbiol Lett. 1998 Apr 1;161(1):1-6. doi: 10.1111/j.1574-6968.1998.tb12921.x.
The maturation of Hydrogenobacter thermophilus cytochrome c552 in the cytoplasm of Escherichia coli is unique among bacterial c-type cytochromes. It is now shown to be matured in a strain lacking the whole set of ccm (cytochrome c maturation) genes that are normally required for c-type cytochrome biogenesis in E. coli. As this cytochrome is thermostable we propose that the apocytochrome c552 has sufficient tertiary structure to allow the haem to slot into its binding pocket, which in turn triggers the spontaneous covalent attachment between apocytochrome c552 and haem. The ccm deletion strain of E. coli, derived from a strain that synthesizes elevated levels of endogenous c-type cytochromes, also produces larger amounts of cytoplasmic H. thermophilus cytochrome c552 than a reference strain. This implies that elevated production of c-type cytochromes is not a consequence of high activity of ccm genes but rather an enhanced ability to supply haem, a view that is supported by the increase in thermophilic cytochrome c552 biogenesis that occurs in a reference strain following supplementation of growth media with delta-aminolevulinic acid.
嗜热栖热菌细胞色素c552在大肠杆菌细胞质中的成熟过程在细菌c型细胞色素中是独特的。现已证明，它能在一株缺乏整套ccm（细胞色素c成熟）基因的菌株中成熟，而这些基因通常是大肠杆菌中c型细胞色素生物合成所必需的。由于这种细胞色素具有热稳定性，我们推测脱辅基细胞色素c552具有足够的三级结构，能使血红素嵌入其结合口袋，进而引发脱辅基细胞色素c552与血红素之间的自发共价连接。该大肠杆菌的ccm缺失菌株源自一株内源性c型细胞色素合成水平较高的菌株，与对照菌株相比，它也能产生更多的细胞质嗜热栖热菌细胞色素c552。这意味着c型细胞色素产量的提高并非ccm基因高活性的结果，而是血红素供应能力增强的体现，补充δ-氨基乙酰丙酸的生长培养基后对照菌株中嗜热细胞色素c552生物合成增加这一现象支持了这一观点。
