In vivo self-hydroxylation of an iron-substituted manganese-dependent extradiol cleaving catechol dioxygenase

Abstract

The homoprotocatechuate 2,3-dioxygenase from Arthrobacter globiformis (MndD) catalyzes the oxidative ring cleavage reaction of its catechol substrate in an extradiol fashion. While this reactivity is more typically associated with nonheme iron enzymes, MndD exhibits an unusual specificity for manganese(II). MndD is structurally very similar to the iron(II)-dependent homoprotocatechuate 2,3-dioxygenase from Brevibacterium fuscum (HPCD), and we have previously shown that both MndD and HPCD are equally active towards substrate turnover with either Fe(II) or Mn(II) [J P Emerson, et al. (2008) Proc Natl Acad Sci USA, 105: 7347–7352]. However, expression of MndD in E. coli under aerobic conditions in the presence of excess iron results in the isolation of inactive blue-green Fe-substituted MndD (BG-FeMndD). Spectroscopic studies indicate that this form of Fe-substituted MndD contains an Fe(III) center with a bound catecholate, which is presumably generated by in vivo self-hydroxylation of a second-sphere tyrosine residue, as found for other self-hydroxylated nonheme iron oxygenases,. The absence of this modification in either the native Mn-containing MndD or Fe-containing HPCD suggests that the metal center of Fe-substituted MndD is able to bind and activate O2 in the absence of its substrate, employing a high-valent oxoiron oxidant to carry out the observed self-hydroxylation chemistry. These results demonstrate that the active site metal in MndD can support two dramatically different O2 activation pathways, further highlighting the catalytic flexibility of enzymes containing a 2-His-1-carboxylate facial triad metal binding motif.

Catechol-Functionalized Chitosan/Iron Oxide Nanoparticle Composite Inspired by Mussel Thread Coating and Squid Beak Interfacial Chemistry

“…These vibrational frequencies have been previously outlined as key features for oxygen−metal chelation, with the 591 and 635 cm −1 indicative of coordination of the metal center by the oxygens on C3 and C4 of the catechol ring, respectively. 6,25,26 The 540 cm −1 band arises upon charge transfer that proceeds only when both phenolic motifs are chelated to a transitional metal as is the case with γ-Fe 2 O 3 -catechol chelation. 26 Upon wetting the samples, the signals associated with chelation remained unchanged even with applied strains 50% that of the strain to failure.…”

Metals, oxidative stress and neurodegeneration: A focus on iron, manganese and mercury

“…There are cases where enzymes, such as epimerases, are thought to use Fe 2+ as a Lewis acid under normal growth conditions but switch to Mn 2+ under oxidative stress. Estradiol dioxygenases have been found to use both Fe 2+ and Mn 2+ (Farquhar et al, 2011). Notably, a specific class of I ribonucleotide reductases (RNRs), which convert nucleotides in deoxynucleotides, have evolved unique biosynthetic pathways to control metallation (Stubbe and Cotruvo, 2011).…”

Role of Secondary Coordination Sphere Residues in Halogenation Catalysis of Non-heme Iron Enzymes

“…Similar observations were seen in ironsubstituted catechol dioxygenase and F208Y ribonucleotide reductase which also purified as a mixture of tyrosine and DOPA containing variants. 43,53 Oxidation of tyrosine to DOPA likely occurs through the formation of the ferryl intermediate. Both hydroxylases and halogenases have evolved to bind their substrates prior to forming the reactive ferryl oxidant.…”