Abstract
Productive biomolecular recognition requires exquisite control of affinity and specificity. Accordingly, nature has devised many strategies to achieve proper binding interactions. Bacterial multicomponent monooxygenases provide a fascinating example, where a diiron hydroxylase must reversibly interact with both ferredoxin and catalytic effector in order to achieve electron transfer and O2 activation during catalysis. Because these two accessory proteins have distinct structures, and because the hydroxylase-effector complex covers the entire surface closest to the hydroxylase diiron centre, how ferredoxin binds to the hydroxylase has been unclear. Here we present high-resolution structures of toluene 4-monooxygenase hydroxylase complexed with its electron transfer ferredoxin and compare them with the hydroxylase-effector structure. These structures reveal that ferredoxin or effector protein binding produce different arrangements of conserved residues and customized interfaces on the hydroxylase in order to achieve different aspects of catalysis.
Highlights
Productive biomolecular recognition requires exquisite control of affinity and specificity
To gain insight into the protein interface used for electron transfer, we determined the structure of the hydroxylase-ferredoxin complex (T4moHC)
Shape complementarity in the deepest portion of the binding interface allows the ferredoxin [2Fe-2S] centre to achieve the closest possible through-space approach to the hydroxylase diiron active site, whereas the unique 4,5-coordinate geometry produced by T4moC binding (Fig. 4c) likely represents a new diiron centre configuration involved in electron transfer
Summary
Productive biomolecular recognition requires exquisite control of affinity and specificity. Toluene 4-monoxygenase (T4MO) is a member of these enzymes, and high-resolution structures of the hydroxylase T4moH (PDB: 3DHG), effectorhydroxylase T4moHD (PDB: 3DHH) and T4moHD-product (PDB: 3Q14) complexes are available[28,29,30,31] These structures reveal conformational changes driven by T4moD binding occur along the substrate access channel, within the active site, and at the diiron centre[28]. The T4moHD complex uses a larger surface area and specific steric contacts to collapse the substrate access channel and place both diiron ligands and active water molecules into a unique configuration presumably poised for O2 activation In combination, these structures provide unique new insight into the ability of protein–protein interactions to optimize configurations of conserved residues and overlapping binding interfaces to achieve different aspects of catalysis
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