Department of Biochemistry, University of Wisconsin, Madison, WI 53706, USA.
Proc Natl Acad Sci U S A. 2012 Jun 26;109(26):10370-5. doi: 10.1073/pnas.1206945109. Epub 2012 Jun 11.
Fe-S clusters are critical prosthetic groups for proteins involved in various critical biological processes. Before being transferred to recipient apo-proteins, Fe-S clusters are assembled on the highly conserved scaffold protein Isu, the abundance of which is regulated posttranslationally on disruption of the cluster biogenesis system. Here we report that Isu is degraded by the Lon-type AAA+ ATPase protease of the mitochondrial matrix, Pim1. Nfs1, the cysteine desulfurase responsible for providing sulfur for cluster formation, is required for the increased Isu stability occurring after disruption of cluster formation on or transfer from Isu. Physical interaction between the Isu and Nfs1 proteins, not the enzymatic activity of Nfs1, is the important factor in increased stability. Analysis of several conditions revealed that high Isu levels can be advantageous or disadvantageous, depending on the physiological condition. During the stationary phase, elevated Isu levels were advantageous, resulting in prolonged chronological lifespan. On the other hand, under iron-limiting conditions, high Isu levels were deleterious. Compared with cells expressing normal levels of Isu, such cells grew poorly and exhibited reduced activity of the heme-containing enzyme ferric reductase. Our results suggest that modulation of the degradation of Isu by the Pim1 protease is a regulatory mechanism serving to rapidly help balance the cell's need for critical iron-requiring processes under changing environmental conditions.
铁硫簇是参与各种关键生物过程的蛋白质的关键辅基。在被转移到受体脱辅基蛋白之前，铁硫簇在高度保守的支架蛋白 Isu 上组装，其丰度在簇生物发生系统被破坏后通过翻译后调控来调节。在这里，我们报告说线粒体基质中的 Lon 型 AAA+ATP 酶蛋白酶 Pim1 会降解 Isu。负责为簇形成提供硫的半胱氨酸脱硫酶 Nfs1 是在从 Isu 上形成或转移簇形成中断后发生的 Isu 稳定性增加所必需的。Isu 和 Nfs1 蛋白之间的物理相互作用，而不是 Nfs1 的酶活性，是增加稳定性的重要因素。对几种情况的分析表明，高 Isu 水平可能有利也可能不利，具体取决于生理状况。在静止期，Isu 水平升高是有利的，导致细胞的chronological 寿命延长。另一方面，在缺铁条件下，高 Isu 水平是有害的。与表达正常水平 Isu 的细胞相比，这些细胞生长不良，血红素酶亚铁还原酶的活性降低。我们的结果表明，通过 Pim1 蛋白酶对 Isu 降解的调节是一种快速帮助平衡细胞在不断变化的环境条件下对关键铁需求过程的需求的调节机制。
