A story of chelatase evolution -: Identification and characterization of a small 13-15-kda "ancestral" cobaltochelatase (CbiXs) in the archaea
A story of chelatase evolution -: Identification and characterization of a small 13-15-kda "ancestral" cobaltochelatase (CbiXs) in the archaea
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DOI：
10.1074/jbc.m302468200
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发表时间：
2003-06-20
影响因子：
4.8
通讯作者：
Warren, MJ
中科院分区：
文献类型：
--
作者：
Brindley, AA;Raux, E;Warren, MJ
在古生物界合成维生素B-12(钴胺)所需的钴络合酶，通过与巨大芽孢杆菌的CbiX的相似性搜索，被鉴定为CbiX。然而，古细菌中的CbiX蛋白比真细菌中发现的CbiX蛋白要短得多，通常一级结构中的氨基酸数量不到一半。因此，较短的CbiX蛋白被称为CbiX(S)，较长的CbiX(L)被称为CbiX。以重组蛋白的形式在大肠杆菌中高效表达了巴氏甲烷链霉菌和热自养甲烷杆菌的CbiX(S)蛋白，并对其进行了鉴定。通过对一株明确的螯合酶缺陷型大肠杆菌的补充研究和体外直接测定，证实了CbiX(S)作为一种西罗盐酸盐钴螯合酶的功能。根据序列比对和保守的活性中心残基，我们认为CbiX(S)可能是一个原始的螯合酶，通过基因复制和随后的变异和选择产生了更大的螯合酶，如CbiX(L)、sirB、CbiK和hemH。提出了一种螯合酶的分类方案。
The cobaltochelatase required for the synthesis of vitamin B-12 ( cobalamin) in the archaeal kingdom has been identified as CbiX through similarity searching with the CbiX from Bacillus megaterium. However, the CbiX proteins in the archaea are much shorter than the CbiX proteins found in eubacteria, typically containing less than half the number of amino acids in their primary structure. For this reason the shorter CbiX proteins have been termed CbiX(S) and the longer versions CbiX(L). The CbiX(S) proteins from Methanosarcina barkeri and Methanobacter thermoautotrophicum were overproduced in Escherichia coli as recombinant proteins and characterized. Through complementation studies of a defined chelatase- deficient strain of E. coli and by direct in vitro assays the function of CbiX(S) as a sirohydrochlorin cobaltochelatase has been demonstrated. On the basis of sequence alignments and conserved active site residues we suggest that CbiX(S) may represent a primordial chelatase, giving rise to larger chelatases such as CbiX(L), SirB, CbiK, and HemH through gene duplication and subsequent variation and selection. A classification scheme for chelatases is proposed.