| 1. |
- Ersmark, Karolina, et al.
(författare)
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C2-symmetric inhibitors of Plasmodium falciparum plasmepsin II : synthesis and theoretical predictions
- 2003
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Ingår i: Bioorganic & Medicinal Chemistry. - 0968-0896 .- 1464-3391. ; 11:17, s. 3723-3733
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Tidskriftsartikel (refereegranskat)abstract
- A series of C(2)-symmetric compounds with a mannitol-based scaffold has been investigated, both theoretically and experimentally, as Plm II inhibitors. Four different stereoisomers with either benzyloxy or allyloxy P1/P1' side chains were studied. Computational ranking of the binding affinities of the eight compounds was carried out using the linear interaction energy (LIE) method relying on a complex previously determined by crystallography. Within both series of isomers the theoretical binding energies were in agreement with the enzymatic measurements, illustrating the power of the LIE method for the prediction of ligand affinities prior to synthesis. The structural models of the enzyme-inhibitor complexes obtained from the MD simulations provided a basis for interpretation of further structure-activity relationships. Hence, the affinity of a structurally similar ligand, but with a different P2/P2' substituent was examined using the same procedure. The predicted improvement in binding constant agreed well with experimental results.
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| 5. |
- Feierberg, Isabella, et al.
(författare)
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Computational modeling of enzymatic keto-enol isomerization reactions
- 2002
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Ingår i: Theoretical Chemistry accounts. - : Springer Science and Business Media LLC. - 1432-881X .- 1432-2234. ; 108:2, s. 71-84
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Tidskriftsartikel (refereegranskat)abstract
- Catalysis of proton abstraction from nonacidic carbon atoms adjacent to a carbonyl or carboxylate group is a fundamental reaction in enzymology that has been extensively studied during the last few decades. Enzymes catalyzing these reactions, which normally involve labile enolic intermediates, need to overcome large pK a differences between the reacting groups as well as high intrinsic free-energy barriers. Here, we present an overview of results from recent computer simulation studies of keto-enol isomerization reactions catalyzed by the enzymes glyoxalase I, triosephopsphate isomerase and ketosteroid isomerase. For all three enzymes it is found that electrostatic stabilization of the transient enolate intermediates, either by charge–charge interactions or by hydrogen bonding, accounts for the main part of the activation free-energy barrier reduction. Another catalytic effect observed in all cases is the reduction of the reorganization energy by the enzyme active site. Some other factors that have been proposed to be important for these reactions are also discussed and evaluated.
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| 6. |
- Feierberg, Isabella
(författare)
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Computational Studies of Enzymatic Enolization Reactions and Inhibitor Binding to a Malarial Protease
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Enolate formation by proton abstraction from an sp3-hybridized carbon atom situated next to a carbonyl or carboxylate group is an abundant process in nature. Since the corresponding nonenzymatic process in water is slow and unfavorable due to high intrinsic free energy barriers and high substrate pKa s, enzymes catalyzing such reaction steps must overcome both kinetic and thermodynamic obstacles. Computer simulations were used to study enolate formation catalyzed by glyoxalase I (GlxI) and 3-oxo-Δ5-steroid isomerase (KSI). The results, which reproduce experimental kinetic data, indicate that for both enzymes the free energy barrier reduction originates mainly from the balancing of substrate and catalytic base pKas. This was found to be accomplished primarily by electrostatic interactions. The results also suggest that the remaining barrier reduction can be explained by the lower reorganization energy in the preorganized enzyme compared to the solution reaction. Moreover, it seems that quantum effects, arising from zero-point vibrations and proton tunnelling, do not contribute significantly to the barrier reduction in GlxI. For KSI, the formation of a low-barrier hydrogen bond between the enzyme and the enolate, which is suggested to stabilize the enolate, was investigated and found unlikely. The low pKa of the catalytic base in the nonpolar active site of KSI may possibly be explained by the presence of a water molecule not detected by experiments. The hemoglobin-degrading aspartic proteases plasmepsinI and plasmepsin II from Plasmodium falciparum have emerged as putative drug targets against malaria. A series of C2- symmetric compounds with a 1,2-dihydroxyethylene scaffold were investigated for plasmepsin affinity, using computer simulations and enzyme inhibition assays. The calculations correctly predicted the stereochemical preferences of the scaffold and the effect of chemical modifications. Calculated absolute binding free energies reproduced experimental data well. As these inhibitors have down to subnanomolar inhibition constants of the plasmepsins and no measurable affinity to human cathepsin D, they constitute promising lead compounds for further drug development.
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| 7. |
- Feierberg, Isabella, et al.
(författare)
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Computer simulation of primary kinetic isotope effects in the proposed rate-limiting step of the glyoxalase I catalyzed reaction
- 2000
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 275:30, s. 22657-22662
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Tidskriftsartikel (refereegranskat)abstract
- The proposed rate-limiting step of the glyoxalase I catalyzed reaction is the proton abstraction from the C1 carbon of the substrate by Glu172. Here we examine primary kinetic isotope effects and the influence of quantum dynamics on this process by computer simulations. The calculations utilize the empirical valence bond method in combination with the molecular dynamics free energy perturbation technique and path integral simulations. For the enzyme-catalyzed reaction a H/D kinetic isotope effect of 5.0 ± 1.3 is predicted in reasonable agreement with the experimental result of about 3. Furthermore, the magnitude of quantum mechanical effects is found to be very similar for the enzyme reaction and the corresponding uncatalyzed process in solution, in agreement with other studies. The problems associated with attaining the required accuracy in order for the present approach to be useful as a diagnostic tool for the study of enzyme reactions are also discussed.
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| 8. |
- Feierberg, Isabella, et al.
(författare)
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The catalytic power of ketosteroid isomerase investigated by computer simulation
- 2002
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 41:52, s. 15728-15735
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Tidskriftsartikel (refereegranskat)abstract
- Ketosteroid isomerase (KSI) catalyzes the isomerization of Delta(5)-3-ketosteroids and Delta(4)-3-ketosteroids at very high rates. Here we examine the principles underlying the catalytic efficiency of KSI by computer simulations using the empirical valence bond method in combination with molecular dynamics free energy perturbation simulations. The simulations reproduce available kinetic and structural data very well and allow us to examine several features of the catalytic mechanism in detail. It is found that about 60% of the rate enhancement is due to stabilization of the negatively charged dienolate intermediate by hydrogen bonding. The critical H-bond between Tyr16 and the intermediate is found to be a normal ionic H-bond with the preferred proton location on the tyrosine residue. The remaining 40% of the catalytic effect originates from a reduction of the reorganization energy of the reaction. The possibility of an active site water molecule occupying the empty cavity adjacent to the catalytic base (Asp40) is also addressed. The existence of such a water molecule could explain how the enzyme manages to maintain a low pK(a) for the general base residue.
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