Estudos teóricos e de modelagem molecular in silico aplicados à interação entre a enzima delta-aminolevulinato desidratase e disselenetos de diarila

Abstract

Delta-aminolevulinic acid dehydratase (δ-ALA-D) is an essential metalloprotein found in several biological processes, since it is able to catalyze the formation of porphobilinogen (PBG), a precursor monopyrol of tetrapyrroles (heme and chlorophyll). This enzyme is sensible to heavy metals and other pro-oxidant agents and, consequently, it has been classically used as a protein marker for lead intoxication. Both in vitro and in vivo studies has shown that the organochalcogen diphenyl diselenide [(PhSe)2] could be a promising drug due to present antioxidant, neuroprotective, anti-inflammatory, anti-atherosclerotic and other activities. Contrariwise, (PhSe)2 could also be toxic because it can inhibit the activity of important sulfhydryl enzymes, including δ-ALA-D. Regarding some experimental data, it has been speculated that mammalian δ-ALA-D inhibition can occur via the oxidation of two vicinal thiols located in it active center site. However, no molecular model had been proposed in order to explain this interaction with details. Thus, we aimed to get a further understanding about the interaction involving δ-ALA-D and diselenides using in silico molecular modeling methods, which are consisted in theoretical methods applied in to represent or mimic the behavior and interaction of ligands and enzymes from their structural and thermodynamic information. Docking simulations indicated an important role for π-π interactions involving Phe208 and cation-π interactions involving Lys199 and Arg209 residues with the aromatic ring of (PhSe)2 and analogs bis 4-(clorophenyl) diselenide, bis 4-(methoxyphenyl)diselenide and bis 3-(trifluorometil(phenyl)diselenide. These interactions allowed an approximation between Se atoms and SH of Cys124 (3.3 3.5 Å). The analogs interacted similarly with the active site of δ-ALAD. According to the quantum method MFCC (Molecular Fractionation with Conjugated Caps), interactions involving (PhSe)2 could occur up to 8.5 Å distance from the centroid of active site. Phe208, Phe79, Cys122, Cys124, Pro125, Asp120, Lys199, Lys252 and Cys132 displayed strong attraction energy to (PhSe)2. The representative molecular model is in accordance with in vitro assays and gives mechanistic support to previous speculative mechanism of inhibition. Phenyl moieties in (PhSe)2 can be strongly attracted by aromatic and positive charged residues from δ-ALA-D active site. This allows the approximation of the reactive electrophile moiety Se-Se to the nucleophile S- groups from Cys122, Cys124 and Cys132, facilitating the release of coordinated Zn(II), thiol oxidation and formation of 2 molecules of phenylselenol (PhSeH). In conclusion, the presence of aromatic moieties in (PhSe)2 and its reactive electrophile moiety Se-Se are crucial to δ-ALA-D inhibition, which leads to thiol oxidation and consequent impairment of its activity.