Structure of human Fe-S assembly subcomplex reveals unexpected cysteine desulfurase architecture and acyl-ACP-ISD11 interactions
Structure of human Fe-S assembly subcomplex reveals unexpected cysteine desulfurase architecture and acyl-ACP-ISD11 interactions
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DOI：
10.1073/pnas.1702849114
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发表时间：
2017-07-03
影响因子：
11.1
通讯作者：
Barondeau, David P.
中科院分区：
文献类型：
--
作者：
Cory, Seth A.;Van Vranken, Jonathan G.;Barondeau, David P.
在真核生物中，硫被半胱氨酸脱硫酶复合体动员并结合到多种生物合成途径中，半胱氨酸脱硫酶复合体由催化亚基(NFS1)、LYR蛋白(ISD11)和酰基载体蛋白(ACP)组成。这种NFS1-ISD11-ACP(SDA)络合物形成铁-硫(Fe-S)组装络合物的核心，并与组装蛋白ISCU2、Frataxin(Fxn)和铁氧还蛋白结合合成Fe-S簇合物。在这里，我们介绍了SDA复合体的结晶学和电子显微镜结构，并结合酶动力学和基于细胞的研究，提供了线粒体半胱氨酸脱硫酶的结构和功能特性。与原核半胱氨酸脱硫酶不同，SDA结构采用了一种意想不到的结构，其中一对ISD11亚基形成了SDA复合体的二聚体核心，这阐明了ISD11在真核组装中的关键作用。不同的四级结构导致底物通道不完全形成和暴露在溶剂中的吡哆醛5‘-磷酸辅因子，为FXN在真核系统中的变构激活剂功能提供了理论基础。结构还揭示了ACP的4‘-磷酸丙氨酸偶联的酰基占据了ISD11的疏水核心，解释了ACP稳定的基础。SDA复合体出人意料的结构为理解含硫生物合成途径与受体蛋白的相互作用、阐明真核生物铁-S簇生物合成的机制细节以及澄清铁-S簇组装缺陷如何导致弗里德里希共济失调等疾病提供了一个框架。此外，我们的结果支持LYR蛋白与酰基-ACP结合作为脂肪酸生物合成的机制来协调呼吸复合体的表达、Fe-S辅因子成熟和活性的锁和钥匙模型。
In eukaryotes, sulfur is mobilized for incorporation into multiple biosynthetic pathways by a cysteine desulfurase complex that consists of a catalytic subunit (NFS1), LYR protein (ISD11), and acyl carrier protein (ACP). This NFS1-ISD11-ACP (SDA) complex forms the core of the iron-sulfur (Fe-S) assembly complex and associates with assembly proteins ISCU2, frataxin (FXN), and ferredoxin to synthesize Fe-S clusters. Here we present crystallographic and electron microscopic structures of the SDA complex coupled to enzyme kinetic and cell-based studies to provide structure-function properties of a mitochondrial cysteine desulfurase. Unlike prokaryotic cysteine desulfurases, the SDA structure adopts an unexpected architecture in which a pair of ISD11 subunits form the dimeric core of the SDA complex, which clarifies the critical role of ISD11 in eukaryotic assemblies. The different quaternary structure results in an incompletely formed substrate channel and solvent-exposed pyridoxal 5'-phosphate cofactor and provides a rationale for the allosteric activator function of FXN in eukaryotic systems. The structure also reveals the 4'-phosphopantetheine-conjugated acyl-group of ACP occupies the hydrophobic core of ISD11, explaining the basis of ACP stabilization. The unexpected architecture for the SDA complex provides a framework for understanding interactions with acceptor proteins for sulfur-containing biosynthetic pathways, elucidating mechanistic details of eukaryotic Fe-S cluster biosynthesis, and clarifying how defects in Fe-S cluster assembly lead to diseases such as Friedreich's ataxia. Moreover, our results support a lock-and-key model in which LYR proteins associate with acyl-ACP as a mechanism for fatty acid biosynthesis to coordinate the expression, Fe-S cofactor maturation, and activity of the respiratory complexes.