title: Theoretical studies on the deacylation step of acylated Candida Antarctica lipase B: structural and reaction pathway analysis.
abstract: The deacylation step of acylated Candida Antarctica lipase B, which was acylated with methylcaprylate (MEC) and acetylcholine (ACh), has been studied by using density functional theory method. Free energies of the entire reaction were calculated for enzyme deacylation by water and hydrogen peroxide that represented hydrolysis and perhydrolysis reactions, respectively. The calculations displayed that a stepwise mechanism there was with the enzyme-product complex being a deep minimum on the free energy surfaces of both of two reactions. The tetrahedral intermediate formation was the rate-determining step of all reactions, which needed 8.1 to 10.5kcalmol(-1) for activation in different reactions. In the second stage of the reaction, fewer free energy barriers, between 4.7 and 5.9kcalmol(-1), were identified to enable the proton transfer from His224 to Ser105 and the breakdown of the tetrahedral intermediate. These calculated activation free energies approved theoretical possibility of both of two reactions for two substrates. Finally, an applied tool examined the interactions role in the stability and energy levels of different chemical species.
authors.affiliation: Biophysical Chemistry Laboratory, Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran. Electronic address: sadeghi.mohammadsadegh@gmail.com.
authors.forename: Mohammad Sadegh
authors.initials: MS
authors.lastname: Sadeghi Googheri
authors.affiliation: Biophysical Chemistry Laboratory, Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran; Research and Technology Center of Biomolecules, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran.
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Housaindokht
authors.affiliation: Department of Chemistry, University of Isfahan, Isfahan, Iran.
authors.forename: Hassan
authors.initials: H
authors.lastname: Sabzyan
mesh_terms: D000215:Acylation; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000737:chemistry; D006868:Hydrolysis; D008049:Lipase / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D005656:Fungal Proteins; D014867:Water; D006861:Hydrogen Peroxide; D008049:Lipase; C431349:lipase B, Candida antarctica
keywords: AIM investigation; DFT calculations; Energy profile; Enzymatic catalysis; Hydrogen bond interactions