Contributions of Zur-Controlled Ribosomal Proteins to Growth under Zinc Starvation Conditions
Contributions of Zur-Controlled Ribosomal Proteins to Growth under Zinc Starvation Conditions
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DOI：
10.1128/jb.00802-09
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发表时间：
2009-10-01
影响因子：
3.2
通讯作者：
Helmann, John D.
中科院分区：
文献类型：
--
作者：
Gabriel, Scott E.;Helmann, John D.
维持细胞内锌水平至关重要，因为锌是许多必需酶的辅助因子，过量会产生毒性。枯草芽孢杆菌 Zur 是一种 Fur 家族阻遏蛋白，控制锌饥饿反应，包括与 L31 和 S14 旁系同源的两种核糖体蛋白（r 蛋白）。生化分析表明，Zur 控制的 r 蛋白（缺少两个 CXXC 金属结合基序）可能在锌限制期间功能性地取代其同源的需锌蛋白。我们在此证明 Zur 调节另一种 r 蛋白旁系同源物 RpmGC (L33c) 的表达，并且使用锌摄取缺陷的菌株，我们研究了所有三种 Zur 调节的 r 蛋白的生理学贡献。在168谱系中，rpmGC是一个含有移码突变的假基因。纠正该突变允许表达功能性 L33c，该功能性 L33c 可以抑制 rpmGA rpmGB（编码 L33a、L33b）双突变体的不良生长表型。类似地，我们提供了支持“故障安全”模型的生理学证据（Y. Natori 等人，Mol. Microbiol. 63: 294-307, 2007），其中 Zur 调节的 S14 旁系同源物 YhzA 在没有足够的锌来支持 S14 功能时允许继续核糖体合成。 L31旁系同源物YtiA可以替代L31并补充rpmE突变体的生长缺陷(Nanamiya等人，Mol.Microbiol.52:273-283)。我们发现，在锌饥饿条件下，YtiA 的去抑制显着增加了细胞的生长，在这些细胞中，预先存在的核糖体携带唯一的 L31 蛋白 RpmE（含锌），但如果它们携带 YtiA（缺乏锌）则不会。这些结果支持 YtiA 在从核糖体中调动锌方面具有直接的生理相关作用。
Maintaining intracellular zinc levels is critical, because zinc serves as a cofactor for many required enzymes and is toxic in excess. Bacillus subtilis Zur, a Fur family repressor, controls the zinc starvation response including two ribosomal proteins (r-proteins) paralogous to L31 and S14. Biochemical analyses suggest that Zur-controlled r-proteins (which lack the two CXXC metal-binding motifs) may functionally replace their cognate zinc-requiring proteins during zinc limitation. We demonstrate here that Zur regulates the expression of an additional r-protein paralog, RpmGC (L33c), and, using strains defective in zinc uptake, we investigate the physiological contributions of all three Zur-regulated r-proteins. In the 168 lineage, rpmGC is a pseudogene containing a frameshift mutation. Correction of this mutation allows expression of a functional L33c that can suppress the poor growth phenotype of an rpmGA rpmGB (encoding L33a, L33b) double mutant. Similarly, we provide physiological evidence in support of the "failsafe" model (Y. Natori et al., Mol. Microbiol. 63: 294-307, 2007) in which the Zur-regulated S14 paralog YhzA allows continued ribosome synthesis when there is insufficient zinc to support S14 function. The L31 paralog YtiA can replace L31 and complement the growth defect of an rpmE mutant (Nanamiya et al., Mol. Microbiol. 52:273-283). We show that, under zinc starvation conditions, derepression of YtiA significantly increases the growth of cells in which preexisting ribosomes carry, as the sole L31 protein, RpmE (containing zinc), but not if they carry YtiA (which lacks zinc). These results support a direct and physiologically relevant role for YtiA in mobilizing zinc from ribosomes.