Understanding the biosynthesis of cofactors is fundamental to the life sciences, yet to date a few important pathways remain unresolved. One example is the redox cofactor pyrroloquinoline quinone (PQQ), which is critical for C1 metabolism in many microorganisms, a disproportionate number of which are opportunistic human pathogens. While the initial and final steps of PQQ biosynthesis, involving PqqD/E and PqqC, have been elucidated, the precise nature and order of the remaining transformations in the pathway are unknown. Here we show evidence that the remaining essential biosynthetic enzyme PqqB is an iron-dependent hydroxylase catalyzing oxygen-insertion reactions that are proposed to produce the quinone moiety of the mature PQQ cofactor. The demonstrated reactions of PqqB are unprecedented within the metallo β-lactamase protein family and expand the catalytic repertoire of nonheme iron hydroxylases. These new findings also generate a nearly complete description of the PQQ biosynthetic pathway.
Bibliographical noteFunding Information:
This work was supported by National Institutes of Health Grants to J.P.K. (GM118117-015), C.M.W. (GM66569), and A.T.I. (1S10OD020062-01). We thank Prof. Nigel Richards for helpful discussion and the initial suggestion that we explore a molecular oxygen insertion mechanism for PqqB with Cys-DOPA. The work used Advanced Photon Source beamline 19-BM and GM/CA 23-ID-B funded in whole or in part with Federal funds from the National Cancer Institute (ACB-12002) and the National Institute of General Medical Sciences (AGM-12006). This research also used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract no. DE-AC02-06CH11357.
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