Evolution of the soluble diiron monooxygenases

Abstract

Based on structural, biochemical, and genetic data, the soluble diiron monooxygenases can be divided into four groups: the soluble methane monooxygenases, the Amo alkene monooxygenase of Rhodococcus corallinus B-276, the phenol hydroxylases, and the fourcomponent alkene/aromatic monooxygenases. The limited phylogenetic distribution of these enzymes among bacteria, together with available genetic evidence, indicates that they have been spread largely through horizontal gene transfer. Phylogenetic analyses reveal that the K-and L-oxygenase subunits are paralogous proteins and were derived from an ancient gene duplication of a carboxylate-bridged diiron protein, with subsequent divergence yielding a catalytic K-oxygenase subunit and a structural L-oxygenase subunit. The oxidoreductase and ferredoxin components of these enzymes are likely to have been acquired by horizontal transfer from ancestors common to unrelated diiron and Rieske center oxygenases and other enzymes. The cumulative results of phylogenetic reconstructions suggest that the alkene/aromatic monooxygenases diverged first from the last common ancestor for these enzymes, followed by the phenol hydroxylases, Amo alkene monooxygenase, and methane monooxygenases.

X-ray Structure of a Hydroxylase−Regulatory Protein Complex from a Hydrocarbon-Oxidizing Multicomponent Monooxygenase, Pseudomonas sp. OX1 Phenol Hydroxylase,

“…Such structural differences are not surprising given the poor sequence conservation for this subunit among the different BMM family members. The function of this subunit, which is absent in some BMMs like alkene monooxygenases, is unclear (2,3,11).…”

“…TMOs and SsoMOs differ slightly since they utilize an additional, Rieske protein to assist with electron transfer between the reductase and hydroxylase components (2,3). The active sites in the resting states of the methane (MMOH) and toluene/o-xylene (ToMOH) monooxygenase hydroxylases contain a diiron(III) center coordinated by four glutamate and two histidine ligands from a four-helix bundle composed of helices B, C, E, and F of the protein α-subunit (8,9).…”

“…A diiron(IV) intermediate has not been detected in any other BMM hydroxylase, but recent work has identified oxygenated diiron(III) species capable of oxidizing aromatic substrates (15). 2 , 3 1 Abbreviations: ACP, acyl carrier protein; AMO, alkene monooxygenase; APS, Advanced Photon Source; BMM, bacterial multicomponent monooxygenase; C2,3O, catechol 2,3-dioxygenase; PH, phenol hydroxylase; PHH, phenol hydroxylase hydroxylase component; PHM, phenol hydroxylase regulatory protein; PHP, phenol hydroxylase reductase; MMOB, methane monooxygenase regulatory protein; MMOH, methane monooxygenase hydroxylase; MMOR, methane monooxygenase reductase; rmsd, root-meansquare deviation; sMMO, soluble methane monooxygenase; SsoMO, hyperthermophilic toluene monooxygenase; SSRL, Stanford Synchrotron Radiation Laboratory; T4MO, toluene 4-monooxygenase; T4MOD, toluene 4-monooxygenase regulatory protein; THFMO, tetrahydrofuran monooxygenase; TMO, toluene monooxygenase; TOM, toluene o-monooxygenase; ToMO, toluene/o-xylene monooxygenase; ToMOD, toluene/o-xylene monooxygenase regulatory protein; ToMOH, toluene/o-xylene monooxygenase hydroxylase. Comparisons between the MMOH and ToMOH structures have provided insight into how the protein scaffold may tune the reactivity and substrate specificity of the diiron center by controlling the access of small molecules to the active site pocket.…”

Kinetic characterization of the soluble butane monooxygenase from Thauera butanivorans, formerly ‘Pseudomonas butanovora’

“…To initiate growth on C 2 -C 9 alkanes, the Gramnegative b-proteobacterium Thauera butanivorans, formerly called 'Pseudomonas butanovora' (Dubbels et al, 2009), expresses a carboxylate-bridged non-haem di-iron monooxygenase, commonly referred to as soluble butane monooxygenase (sBMO) (Sluis et al, 2002;Takahashi et al, 1980). sBMO belongs to a family of bacterial multicomponent monooxygenases which includes soluble methane monooxygenases (sMMOs), phenol hydroxylases (PHs) and aromatic/alkene monooxygenases (TMOs) (Leahy et al, 2003;Sluis et al, 2002). Due to their unusually large substrate ranges, these powerful oxidizers are of particular interest for their potential in bioremediation (Enzien et al, 1994;Halsey et al, 2007;Parales et al, 2002;Smith & Dalton, 2004) and their ability to serve as industrial biocatalysts (Burton, 2003;Parales et al, 2002).…”

Soluble expression and purification of the oxidoreductase component of toluene 4-monooxygenase

“…The BMMs utilize a soluble terminal hydroxylase to oxidize a variety of hydrocarbons as the initial step in their metabolism [4]. The BMM family has been divided into four groups: soluble methane monooxygenases (MMO), alkene monooxygenases, phenol hydroxylases, and alkene/aromatic hydroxylases [4].…”