Assignment of EPR transitions in a manganese-containing lipoxygenase and prediction of local structure

Abstract

A new variant of lipoxygenases, one containing manganese instead of iron, is characterized by electron paramagnetic resonance (EPR) at two frequencies. In the manganous state (S(e) = 5/2), maganese lipoxygenase (MnLO) yields very broad X-band (9.2 GHz) EPR signals, extending over about 800 mT. In contrast, at W-band (94 GHz), the signal is much simplified, consisting of nested transitions centered near the free electron g-value. Computer simulation has been employed to derive estimates of the zero-field splittings for MnLO, with data from these two EPR frequencies. The general features of both X- and W-band spectra are fit, first, by simulations with S(e) = 5/2, but no nuclear hyperfine splitting. The simulations are then refined by inclusion of the hyperfine splitting. On the basis of the simulations, the ranges of zero-field splitting parameters are D = +0.07 to +0.10 cm(-1), and E/D = 0.13 to 0.23. Comparison of the value of D for MnLO with that of other manganese-containing proteins suggests that MnLO has three N-ligands to the metal center and O-ligands in the remainder of 6 coordination positions. The coordination environment of MnLO is similar to that in iron lipoxygenases.

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

“…(1a) (1b) Other examples of such mononuclear redox-active enzymes include the manganese peroxidase responsible for lignin degradation by white-rot fungus [10][11][12]; a unique Mndependent form of lipoxygenase [13][14][15][16]; oxalate decarboxylase [17,18]; as well as an extradiol catechol dioxygenase [19][20][21]. …”

“…Many Mn-dependent enzymes take advantage o f the rich redox chemistry available to the metal, accessing the +2, +3, +4, and perhaps even the +5 oxidation states during their turnover. For example, Mn-superoxide dismutase (MnSOD), which detoxifies the cell of the superoxide radical , cycles between the Mn(II) and Mn(III) oxidation states via the ping-pong type mechanism shown below [5][6][7][8][9].(1a) (1b) Other examples of such mononuclear redox-active enzymes include the manganese peroxidase responsible for lignin degradation by white-rot fungus [10][11][12]; a unique Mndependent form of lipoxygenase [13][14][15][16]; oxalate decarboxylase [17,18]; as well as an extradiol catechol dioxygenase [19][20][21]. …”

Manganese lipoxygenase of F. oxysporum and the structural basis for biosynthesis of distinct 11-hydroperoxy stereoisomers

“…The prototype of the MnLOX family is 13 R -MnLOX of the take-all fungus of wheat, Gaeumannomyces graminis (21)(22)(23)(24). Other members are 9 S -MnLOX of the rice stem root fungus, Magnaporthe salvinii ( 25 ), Mo-MnLOX of the rice blast fungus, Magnaporthe oryzae (A. Wennman et al, unpublished observation), and 13-MnLOX of Aspergillus fumigatus and homologs within Fusarium, Colletotrichum, Aspergillus, and Penicillium ( 11,12,22,23 ) ( Fig.…”

Factors influencing the rearrangement of bis-allylic hydroperoxides by manganese lipoxygenase

“…At the end of lipoxygenation, 11-HPODE is transformed to 13-HPODE by Mn-LOX (15). Electron paramagnetic resonance analysis suggests that the catalytic metal redox cycles (Mn 21 /Mn 31 ) between the resting and active forms of the enzyme, in analogy with Fe-lipoxygenases, and that the metal coordinating residues are virtually identical (16)(17)(18)(19). To date, the oxygenation of bis-allylic carbons by Fe-lipoxygenases has only been reported for the recombinant lipoxygenase domain of allene oxide synthase of Plexaura homomalla, which transforms 20:3n-6 to the bis-allylic hydroperoxide at C-10 (?5%) and to the allylic hydroperoxide at C-8 (20).…”