ATPase activity of magnesium chelatase subunit I is required to maintain subunit D in vivo
ATPase activity of magnesium chelatase subunit I is required to maintain subunit D in vivo
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DOI：
10.1111/j.1432-1033.2004.04143.x
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发表时间：
2004-06-01
期刊：
影响因子：
--
通讯作者：
Hansson, M
中科院分区：
文献类型：
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作者：
Lake, V;Olsson, U;Hansson, M
在叶绿素的生物合成过程中，Mg 2+通过镁螯合酶插入到原卟啉IX中。这种酶由三种不同的亚基组成，分别约为40、70和140 kDa。分析了7个大麦突变体中40 kDa镁螯合酶亚基的缺陷，发现该亚基对于维持70 kDa亚基而不是140 kDa亚基是必不可少的。40 kDa亚基已被证明属于称为“与各种细胞活性相关的ATP酶”的蛋白质家族，已知其形成作为分子伴侣起作用的环状寡聚复合物。七个大麦突变体中有三个是半显性错义突变，导致40 kDa蛋白中保守氨基酸残基的变化。使用红细菌荚膜40和70 kDa镁螯合酶亚基，我们分析了这些突变的影响。虽然没有ATP酶活性，但缺陷的40 kDa亚基仍然可以与70 kDa蛋白结合。结合依赖于Mg ~（2+）和ATP或ADP。我们的研究表明，40 kDa的亚基作为一个伴侣的功能，是必不可少的70 kDa的亚基在体内的生存。我们的结论是，40 kDa的亚基的ATP酶活性是必不可少的这一功能，这两个亚基之间的结合是不足以维持70 kDa的亚基在细胞中。ATP酶缺陷的40 kDa蛋白未能参与螯合后的40和70 kDa亚基的协会的步骤。这一步骤可能涉及响应ATP水解的复合物的构象变化。
During biosynthesis of chlorophyll, Mg2+ is inserted into protoporphyrin IX by magnesium chelatase. This enzyme consists of three different subunits of approximate to 40, 70 and 140 kDa. Seven barley mutants deficient in the 40 kDa magnesium chelatase subunit were analysed and it was found that this subunit is essential for the maintenance of the 70 kDa subunit, but not the 140 kDa subunit. The 40 kDa subunit has been shown to belong to the family of proteins called 'ATPases associated with various cellular activities', known to form ring-shaped oligomeric complexes working as molecular chaperones. Three of the seven barley mutants are semidominant mis-sense mutations leading to changes of conserved amino acid residues in the 40 kDa protein. Using the Rhodobacter capsulatus 40 and 70 kDa magnesium chelatase subunits we have analysed the effect of these mutations. Although having no ATPase activity, the deficient 40 kDa subunit could still associate with the 70 kDa protein. The binding was dependent on Mg2+ and ATP or ADP. Our study demonstrates that the 40 kDa subunit functions as a chaperon that is essential for the survival of the 70 kDa subunit in vivo. We conclude that the ATPase activity of the 40 kDa subunit is essential for this function and that binding between the two subunits is not sufficient to maintain the 70 kDa subunit in the cell. The ATPase deficient 40 kDa proteins fail to participate in chelation in a step after the association of the 40 and 70 kDa subunits. This step presumably involves a conformational change of the complex in response to ATP hydrolysis.