Estudo das propriedades estruturais e eletrônicas da forma particulada da enzima metano monooxigenase (pMMO)

Abstract

The particulate form of the enzyme methane monooxygenase (pMMO) is the most abundant form found in methanotrophic organisms (organisms that use methane as an energy source), in addition to the particulate form, this enzyme can also be found in soluble form (sMMO, less abundant). These organisms are responsible for converting methane to methanol under ambient conditions. PMMO even though it is the most abundant form of this class of enzymes, there are still discussions about its catalytic site, such as whether or not there is water in its first coordination sphere (considering that the catalytic site has great exposure to the solvent). The pMMO has a characteristic similar to another class of enzymes called Lytic Polysaccharide Monooxygenases (LPMO) (LPMO acts on the oxidative breakdown of C-H bonds in polysaccharides promoting the degradation of these biopolymers), both have a coordinated histidine residue via "histidine brace" mode. Due to this structural similarity between the active sites of these enzymes, as well as the respective mechanisms of action (oxidation of alkanes and sugars), it has provided a basis for the hypothesis that the catalytic site of pMMO may actually be a mononuclear copper center coordinated by three histidines and not a binuclear copper center, as previously thought. In this work, was investigated at molecular level the structural and electronic properties of the copper mononuclear site of the enzyme pMMO. The combination of molecular dynamics results and calculations of electronic paramagnetic resonance (EPR) parameters performed using the density functional theory, and comparisons with experimental EPR data, led to the proposition that the pMMO catalytic site is a mononuclear copper complex coordinated by the residues His33, His137, and His139 on the equatorial axis and by two water molecules on the axial axis, with one of these water molecules being more labile which may suggest looser coordination to the copper ion, which over time, under the presence of the solvent medium, the pMMO site alternates between a distorted octahedral structure and a pyramid structure with a square base with coordination 5. A study with three exchange-correlation functionals revealed that the BHANDHLYP functional presented the best performance for calculating EPR parameters.