Controlled expression of nif and isc iron-sulfur protein maturation components reveals target specificity and limited functional replacement between the two systems
Controlled expression of nif and isc iron-sulfur protein maturation components reveals target specificity and limited functional replacement between the two systems
复制标题
DOI：
10.1128/jb.01734-06
复制
发表时间：
2007-04-01
影响因子：
3.2
通讯作者：
Dean, Dennis R.
中科院分区：
文献类型：
--
作者：
Dos Santos, Patricia C.;Johnson, Deborah C.;Dean, Dennis R.
固氮生物棕色固氮菌含有至少两个催化[Fe-S]簇形成的系统。其中一个系统是由nif基因编码的，其产物提供固氮酶成熟所需的[Fe-S]簇。另一个系统由isc基因编码，其产物是参与一般代谢过程的[Fe-S]蛋白成熟所必需的。这两种系统的相似之处在于它们包括用于硫的移动的酶（NifS或IscS）和在其上形成[Fe-S]簇的组装支架（NifU或IscU）。Nif系统的正常细胞水平为固氮酶的成熟提供[Fe-S]簇，也不能为其他细胞[Fe-S]蛋白的成熟提供[Fe-S]簇。相反，当在正常生理水平下产生时，Isc系统不能为固氮酶的成熟提供[Fe-S]簇。在目前的工作中，我们发现，这种针对IscU的靶特异性可以通过提高NifU的产量来克服。我们还发现，如果细胞在低氧条件下培养，NifU在正常水平表达时能够部分取代IscU的功能。与IscU的情况相反，我们不能建立IscS的功能可以被NifS取代的条件。我们还发现，升高的表达的Isc组件，作为一个结果的监管iscR基因的缺失，提高了固氮生长的能力，无论是NifU或NifS缺陷的菌株。
The nitrogen-fixing organism Azotobacter vinelandii contains at least two systems that catalyze formation of [Fe-S] clusters. One of these systems is encoded by nif genes, whose products supply [Fe-S] clusters required for maturation of nitrogenase. The other system is encoded by isc genes, whose products are required for maturation of [Fe-S] proteins that participate in general metabolic processes. The two systems are similar in that they include an enzyme for the mobilization of sulfur (NifS or IscS) and an assembly scaffold (NifU or IscU) upon which [Fe-S] clusters are formed. Normal cellular levels of the Nif system, which supplies [Fe-S] clusters for the maturation of nitrogenase, cannot also supply [Fe-S] clusters for the maturation of other cellular [Fe-S] proteins. Conversely, when produced at the normal physiological levels, the Isc system cannot supply [Fe-S] clusters for the maturation of nitrogenase. In the present work we found that such target specificity for IscU can be overcome by elevated production of NifU. We also found that NifU, when expressed at normal levels, is able to partially replace the function of IscU if cells are cultured under low-oxygen-availability conditions. In contrast to the situation with IscU, we could not establish conditions in which the function of IscS could be replaced by NifS. We also found that elevated expression of the Isc components, as a result of deletion of the regulatory iscR gene, improved the capacity for nitrogen-fixing growth of strains deficient in either NifU or NifS.