A Carboxylate Shift Regulates Dioxygen Activation by the Diiron Nonheme beta-Hydroxylase CmlA upon Binding of a Substrate-Loaded Nonribosomal Peptide Synthetase.Jasniewski, A.J., Knoot, C.J., Lipscomb, J.D., Que, L.
(2016) Biochemistry 55: 5818-5831
- PubMed: 27668828
- DOI: 10.1021/acs.biochem.6b00834
- Primary Citation of Related Structures:
- PubMed Abstract:
The first step in the nonribosomal peptide synthetase (NRPS)-based biosynthesis of chloramphenicol is the β-hydroxylation of the precursor l-p-aminophenylalanine (l-PAPA) catalyzed by the monooxygenase CmlA. The active site of CmlA contains a dinucle ...
The first step in the nonribosomal peptide synthetase (NRPS)-based biosynthesis of chloramphenicol is the β-hydroxylation of the precursor l-p-aminophenylalanine (l-PAPA) catalyzed by the monooxygenase CmlA. The active site of CmlA contains a dinuclear iron cluster that is reduced to the diferrous state (WT R ) to initiate O 2 activation. However, rapid O 2 activation occurs only when WT R is bound to CmlP, the NRPS to which l-PAPA is covalently attached. Here the X-ray crystal structure of WT R is reported, which is very similar to that of the as-isolated diferric enzyme in which the irons are coordinately saturated. X-ray absorption spectroscopy is used to investigate the WT R cluster ligand structure as well as the structures of WT R in complex with a functional CmlP variant (CmlP AT ) with and without l-PAPA attached. It is found that formation of the active WT R :CmlP AT -l-PAPA complex converts at least one iron of the cluster from six- to five-coordinate by changing a bidentately bound amino acid carboxylate to monodentate on Fe1. The only bidentate carboxylate in the structure of WT R is E377. The crystal structure of the CmlA variant E377D shows only monodentate carboxylate coordination. Reduced E377D reacts rapidly with O 2 in the presence or absence of CmlP AT -l-PAPA, showing loss of regulation. However, this variant fails to catalyze hydroxylation, suggesting that E377 has the dual role of coupling regulation of O 2 reactivity with juxtaposition of the substrate and the reactive oxygen species. The carboxylate shift in response to substrate binding represents a novel regulatory strategy for oxygen activation in diiron oxygenases.
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455.,Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455.,Department of Biochemistry Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455.