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Crystal structure of SznF from Streptomyces achromogenes var. streptozoticus NRRL 2697 with a diiron(II) central domain cofactor
Structural highlights
FunctionPublication Abstract from PubMedIn biosynthesis of the pancreatic cancer drug streptozotocin, the tridomain nonheme-iron oxygenase SznF hydroxylates N(delta) and N(omega)' of N(omega)-methyl-l-arginine before oxidatively rearranging the triply modified guanidine to the N-methyl-N-nitrosourea pharmacophore. A previously published structure visualized the monoiron cofactor in the enzyme's C-terminal cupin domain, which promotes the final rearrangement, but exhibited disorder and minimal metal occupancy in the site of the proposed diiron cofactor in the N-hydroxylating heme-oxygenase-like (HO-like) central domain. We leveraged our recent observation that the N-oxygenating micro-peroxodiiron(III/III) intermediate can form in the HO-like domain after the apo protein self-assembles its diiron(II/II) cofactor to solve structures of SznF with both of its iron cofactors bound. These structures of a biochemically validated member of the emerging heme-oxygenase-like diiron oxidase and oxygenase (HDO) superfamily with intact diiron cofactor reveal both the large-scale conformational change required to assemble the O(2)-reactive Fe(2)(II/II) complex and the structural basis for cofactor instability-a trait shared by the other validated HDOs. During cofactor (dis)assembly, a ligand-harboring core helix dynamically (un)folds. The diiron cofactor also coordinates an unanticipated Glu ligand contributed by an auxiliary helix implicated in substrate binding by docking and molecular dynamics simulations. The additional carboxylate ligand is conserved in another N-oxygenating HDO but not in two HDOs that cleave carbon-hydrogen and carbon-carbon bonds to install olefins. Among approximately 9,600 sequences identified bioinformatically as members of the emerging HDO superfamily, approximately 25% conserve this additional carboxylate residue and are thus tentatively assigned as N-oxygenases. Structure and assembly of the diiron cofactor in the heme-oxygenase-like domain of the N-nitrosourea-producing enzyme SznF.,McBride MJ, Pope SR, Hu K, Okafor CD, Balskus EP, Bollinger JM Jr, Boal AK Proc Natl Acad Sci U S A. 2021 Jan 26;118(4):e2015931118. doi: , 10.1073/pnas.2015931118. PMID:33468680[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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