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Abstract:
The Mo-flavo-Fe/S-dependent heterohexameric protein complex 4-hydroxybenzoyl-CoA reductase (4-HBCR, dehydroxylating) is a central enzyme of the anaerobic degradation of phenolic compounds and belongs to the xanthine oxidase (XO) family of molybdenum enzymes. Its X-ray structure was established at 1.6 Å resolution. The most pronounced difference between 4-HBCR and other structurally characterized members of the XO family is the insertion of 40 amino acids within the β subunit, which carries an additional [4Fe-4S] cluster at a distance of 16.5 Å to the isoalloxazine ring of FAD. The architecture of 4-HBCR and concomitantly performed electron transfer rate calculations suggest an inverted electron transfer chain from the donor ferredoxin via the [4Fe-4S] cluster to the Mo over a distance of 55 Å. The binding site of 4-hydroxybenzoyl-CoA is located in an 18 Å long channel lined up by several aromatic side chains around the aromatic moiety, which are proposed to shield and stabilize the postulated radical intermediates during catalysis.
