Crystal Structure of Bacillus cereus Class Ib Ribonucleotide Reductase Di-iron NrdF in Complex with NrdI

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• 作者：Marta Hammerstad ; Hans-Petter Hersleth ; Ane B. Tomter ; ?smund K. R?hr ; K. Kristoffer Andersson
• 刊名：ACS Chemical Biology
• 出版年：2014
• 出版时间：February 21, 2014
• 年：2014
• 卷：9
• 期：2
• 页码：526-537
• 全文大小：674K
• ISSN：1554-8937

文摘

Class Ib ribonucleotide reductases (RNRs) use a dimetal-tyrosyl radical (Y鈥? cofactor in their NrdF (尾₂) subunit to initiate ribonucleotide reduction in the NrdE (伪₂) subunit. Contrary to the diferric tyrosyl radical (Fe^III₂-Y鈥? cofactor, which can self-assemble from Fe^II₂-NrdF and O₂, generation of the Mn^III₂-Y鈥?cofactor requires the reduced form of a flavoprotein, NrdI_hq, and O₂ for its assembly. Here we report the 1.8 脜 resolution crystal structure of Bacillus cereus Fe₂-NrdF in complex with NrdI. Compared to the previously solved Escherichia coli NrdI-Mn^II₂-NrdF structure, NrdI and NrdF binds similarly in Bacillus cereus through conserved core interactions. This protein鈥損rotein association seems to be unaffected by metal ion type bound in the NrdF subunit. The Bacillus cereus Mn^II₂-NrdF and Fe₂-NrdF structures, also presented here, show conformational flexibility of residues surrounding the NrdF metal ion site. The movement of one of the metal-coordinating carboxylates is linked to the metal type present at the dimetal site and not associated with NrdI-NrdF binding. This carboxylate conformation seems to be vital for the water network connecting the NrdF dimetal site and the flavin in NrdI. From these observations, we suggest that metal-dependent variations in carboxylate coordination geometries are important for active Y鈥?cofactor generation in class Ib RNRs. Additionally, we show that binding of NrdI to NrdF would structurally interfere with the suggested 伪₂尾₂ (NrdE-NrdF) holoenzyme formation, suggesting the potential requirement for NrdI dissociation before NrdE-NrdF assembly after NrdI-activation. The mode of interactions between the proteins involved in the class Ib RNR system is, however, not fully resolved.