The Structure of a Designed Diiron(III) Protein: Implications for Cofactor Stabilization and Catalysis

摘要

The de novo design of model metalloproteins provides a powerful approach to examine the functional consequences ofmetal cofactor–protein interactions.[1, 2] Despite extensivework in this area, to date the structures of designed nonhemeFe proteins with bound cofactors have not been determined, rendering it difficult to fully develop structure–function relationships. Here we investigate structural properties of diiron(III) DF2t.[3] DF2t is a dimeric member of the due-ferri (DF) family of highly simplified models[3] of the more complex natural diiron enzymes. These systems, which include methane monooxygenase (MMOH),[4] ribonucleotide reductase (RNRR2),[5] and stearoyl ACP D9-desaturase (D9D)[6] show highly similar ligand sets (almost invariably, 4-Glu,2-His) and encapsulate the diiron cofactors within fourhelix bundles (Table 1).[7] As shown for the natural enzymes, DF2t binds two iron(II) ions using a 4-Glu,2-His ensemble to generate an O2-reactive binuclear cluster. The spectroscopic properties of the diiron(III) DF2t product implicate an oxobridged cofactor, structurally akin to those presented by thediiron(III) enzymes.[8] The crystallographic structure of thediiron(III) DF2t cofactor is presented here, providing a simplified model of diiron enzymes.