Essential histidine pairs indicate conserved haem binding in epsilonproteobacterial cytochrome c haem lyases.
Essential histidine pairs indicate conserved haem binding in epsilonproteobacterial cytochrome c haem lyases.
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DOI：
10.1099/mic.0.042838-0
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发表时间：
2010-12
期刊：
影响因子：
--
通讯作者：
Simon J
中科院分区：
文献类型：
--
作者：
Kern M;Scheithauer J;Kranz RG;Simon J
细菌细胞色素c的成熟发生在细胞质膜外，需要通过膜转运haem b，并依赖于膜结合的细胞色素c裂解酶(CCHL)，CCHL是一种催化haem b与凋亡素c共价结合的酶。CcsBA型CCHls被认为是一种血红素转运体，它含有位于膜不同侧面的两个组氨酸配位形成的血红素b配位。琥珀酸假单胞菌细胞含有三种CcsBA型CCHL同工酶(NrfI、CcsA1和CcsA2)，已知它们对细胞色素的特异性不同，并明显识别不同的Hem c结合基序，如CX2CH(由CcsA2)、CX2CK(由NrfI)和CX15CH(由CcsA1)。在本研究中，每一个产琥珀酸假单胞菌CCHL中保守的组氨酸残基分别被丙氨酸取代。对产琥珀酸假单胞菌NrfI和CcsA1变异体的研究表明，一组四种组氨酸对于成熟专门的多毛细胞色素c NRFA和MCCA分别是必不可少的。在大肠杆菌中产生的琥珀酸假单胞菌CcsA2变异体的功能也被发现依赖于这四个保守的组氨酸残基。在产琥珀酸假单胞菌和大肠埃希氏菌的生长介质中，咪唑的存在挽救了大多数组氨酸变异体的细胞色素c生物合成活性，尽管程度不同，从而意味着每个CCHL中存在两个功能不同的组氨酸对。这些数据支持一个模型，在该模型中，两个保守的haem b结合位点参与了CcsBA型CCHL催化的血红素转运。
Bacterial cytochrome c maturation occurs at the outside of the cytoplasmic membrane, requires transport of haem b across the membrane, and depends on membrane-bound cytochrome c haem lyase (CCHL), an enzyme that catalyses covalent attachment of haem b to apocytochrome c. Epsilonproteobacteria such as Wolinella succinogenes use the cytochrome c biogenesis system II and contain unusually large CCHL proteins of about 900 amino acid residues that appear to be fusions of the CcsB and CcsA proteins found in other bacteria. CcsBA-type CCHLs have been proposed to act as haem transporters that contain two haem b coordination sites located at different sides of the membrane and formed by histidine pairs. W. succinogenes cells contain three CcsBA-type CCHL isoenzymes (NrfI, CcsA1 and CcsA2) that are known to differ in their specificity for apocytochromes and apparently recognize different haem c binding motifs such as CX2CH (by CcsA2), CX2CK (by NrfI) and CX15CH (by CcsA1). In this study, conserved histidine residues were individually replaced by alanine in each of the W. succinogenes CCHLs. Characterization of NrfI and CcsA1 variants in W. succinogenes demonstrated that a set of four histidines is essential for maturing the dedicated multihaem cytochromes c NrfA and MccA, respectively. The function of W. succinogenes CcsA2 variants produced in Escherichia coli was also found to depend on each of these four conserved histidine residues. The presence of imidazole in the growth medium of both W. succinogenes and E. coli rescued the cytochrome c biogenesis activity of most histidine variants, albeit to different extents, thereby implying the presence of two functionally distinct histidine pairs in each CCHL. The data support a model in which two conserved haem b binding sites are involved in haem transport catalysed by CcsBA-type CCHLs.
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影响因子：
4.8
作者：
Dreyfuss, BW;Hamel, PP;Merchant, S
通讯作者：
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影响因子：
5.6
作者：
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DOI：
10.1073/pnas.0903132106
发表时间：
2009-06-23
影响因子：
11.1
作者：
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通讯作者：
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影响因子：
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作者：
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