Biomedical subjects

Hwangseo Park

Publications and source records attributed to Hwangseo Park.

11 recordsLinked to original sources

PubMed2006

Critical assessment of the automated AutoDock as a new docking tool for virtual screening.

A major problem in virtual screening concerns the accuracy of the binding free energy between a target protein and a putative ligand. Here we report an example supporting the outperformance of the AutoDock scoring function in virtual screening in comparison to the other popular docking programs. The original AutoDock program is in itself inefficient to be used in virtual screening because the grids of interaction energy have to be calculated for each putative ligand in chemical database. However, the automation of the AutoDock program with the potential grids defined in common for all putative ligands leads to more than twofold increase in the speed of virtual database screening. The utility of the automated AutoDock in virtual screening is further demonstrated by identifying the actual inhibitors of various target enzymes in chemical databases with accuracy higher than the other docking tools including DOCK and FlexX. These results exemplify the usefulness of the automated AutoDock as a new promising tool in structure-based virtual screening.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed2005

Structural and dynamical basis of broad substrate specificity, catalytic mechanism, and inhibition of cytochrome P450 3A4.

Cytochrome P450 (CYP) 3A4 is responsible for the oxidative degradation of more than 50% of clinically used drugs. By means of molecular dynamics simulations with the newly developed force field parameters for the heme-thiolate group and its dioxygen adduct, we examine the differences in structural and dynamic properties between CYP3A4 in the resting form and its complexes with the substrate progesterone and the inhibitor metyrapone. The results indicate that the broad substrate specificity of CYP3A4 stems from the malleability of a loop (residues 211-218) that resides in the vicinity of the channel connecting the active site and bulk solvent. However, the high-amplitude motion of the flexible loop is found to be damped out upon binding of the inhibitor or the substrate in the active site. In the resting form of CYP3A4, a structural water molecule is bound to the sixth coordination position of the heme iron, stabilizing the octahedral coordination geometry. In addition to the direct coordination of metyrapone to the heme iron, the hydrogen bond interaction between the inhibitor carbonyl group and the side chain of Ser119 also contributes significantly to stabilizing the CYP3A4-metyrapone complex. On the other hand, progesterone is stabilized in the active site by the formation of two hydrogen bonds with Ser119 and Arg106, as well as by the van der Waals interactions with the heme and hydrophobic residues. The structural and dynamic features of the CYP3A4-progesterone complex indicate that the oxidative degradation of progesterone occurs through hydroxylation at the C16 position by the reactive oxygen coordinated to the heme iron.

Cytochrome P-450 CYP3A↗

PubMed2005

Hybrid QM/MM and DFT investigations of the catalytic mechanism and inhibition of the dinuclear zinc metallo-beta-lactamase CcrA from Bacteroides fragilis.

Based on hybrid QM/MM molecular dynamics simulation and density functional theoretical (DFT) calculations, we investigate the mechanistic and energetic features of the catalytic action of dizinc metallo-beta-lactamase CcrA from Bacteroides fragilis. The 200 ps QM/MM simulation of the CcrA enzyme in complex with nitrocefin shows that the substrate beta-lactam moiety is directed toward the active site dizinc center through the interactions of aminocarbonyl and carboxylate groups with the two active site zinc ions and the two conserved residues, Lys167 and Asn176. From the determination of the potential energy profile of a relevant enzymatic reaction model, it is found that the nucleophilic displacement reaction step proceeds with a low-barrier height, leading to the formation of an energetically favored reaction intermediate. The results also show that the high catalytic activity of the CcrA enzyme stems from a simultaneous operation of three catalytic components: activation of the bridging hydroxide nucleophile by zinc-coordinated Asp86; polarization of the substrate aminocarbonyl group by the first zinc ion; stabilization of the negative charge developed on the departing amide nitrogen by the second zinc ion. Consistent with the previous experimental finding that the proton-transfer reaction step is rate-limiting, the activation energy of the second step is found to be 1.6 kcal/mol higher than that of the first step. Finally, through an examination of the structural and energetic features of binding of a thiazolidinecarboxylic acid inhibitor to the active site dizinc center, a two-step inhibition mechanism involving a protonation-induced ligand exchange reaction is proposed for the inhibitory action of a tight-binding inhibitor possessing a thiol group.

Bacterial Proteins↗

PubMed2005

Force field design and molecular dynamics simulations of the carbapenem- and cephamycin-resistant dinuclear zinc metallo-beta-lactamase from Bacteroides fragilis and its complex with a biphenyl tetrazole inhibitor.

On the basis of molecular dynamics simulations, we investigate the dynamic properties of the carbapenem- and cephamycin-resistant dinuclear zinc metallo-beta-lactamase from Bacteroides fragilis and its complex with a biphenyl tetrazole inhibitor, 2-butyl-6-hydroxy-3-[2'-(1H-tetrazol-5-yl)biphenyl-4-ylmethyl]-3H-quinazolin-4-one 1 (L-159061). The results obtained with the newly developed force field parameters for the coordination environment of the catalytic zinc ions show that the active site gorge comprising major and minor loops gets deeper and narrower upon binding of the inhibitor, which supports the previous experimental implication that the structural flexibility of the loop structures plays a significant role in enzymatic action. In the presence of the inhibitor, the Trp32 side chain at the apex of the major loop covers the entrance of active site channel, thereby contributing to the stabilization of the enzyme-inhibitor complex. In addition to a direct coordination of the inhibitor tetrazole ring to the second zinc ion in the active site, the hydrogen bonding of Lys167 to the inhibitor carbonyl group and hydrophobic interactions between the inhibitor and side chains of loop residues prove to be significant binding forces of the enzyme-inhibitor complex.

Anti-Bacterial Agents↗

PubMed2005

Peptide-cleaving catalyst selective for peptide deformylase.

A peptide-cleaving catalyst selective for peptide deformylase (PDF) was obtained from a library containing about 15 000 catalyst candidates. The catalyst cleaved the polypeptide backbone of PDF at Gln(152)-Arg(153). Docking simulations suggested multiple modes of interactions in the complex formed between the catalyst and PDF.

Amides↗

PubMed2005

Free energy perturbation approach to the critical assessment of selective cyclooxygenase-2 inhibitors.

The discovery of selective cyclooxygenase-2 (COX-2) inhibitors represents a major achievement of the efforts over the past few decades to develop therapeutic treatments for inflammation. To gain insights into designing new COX-2-selective inhibitors, we address the energetic and structural basis for the selective inhibition of COX isozymes by means of a combined computational protocol involving docking experiment, force field design for the heme prothetic group, and free energy perturbation (FEP) simulation. We consider both COX-2- and COX-1-selective inhibitors taking the V523I mutant of COX-2 to be a relevant structural model for COX-1 as confirmed by a variety of experimental and theoretical evidences. For all COX-2-selective inhibitors under consideration, we find that free energies of binding become less favorable as the receptor changes from COX-2 to COX-1, due to the weakening and/or loss of hydrogen bond and hydrophobic interactions that stabilize the inhibitors in the COX-2 active site. On the other hand, COX-1-selective oxicam inhibitors gain extra stabilization energy with the change of residue 523 from valine to isoleucine because of the formations of new hydrogen bonds in the enzyme-inhibitor complexes. The utility of the combined computational approach, as a valuable tool for in silico screening of COX-2-selective inhibitors, is further exemplified by identifying the physicochemical origins of the enantiospecific selective inhibition of COX-2 by alpha-substituted indomethacin ethanolamide inhibitors.

Amino Acid Sequence↗

PubMed2004

Prediction of the mutation-induced change in thermodynamic stabilities of membrane proteins from free energy simulations.

Comparative protein structure modeling and free energy perturbation simulation have been applied in a consecutive manner to investigate the mutation-induced stabilization of membrane proteins (MPs) in aqueous solution without knowledge of their three-dimensional structures. The calculated difference in protein solvation free energy between the wild type and a mutant compares well with their relative thermodynamic stabilities in solution. For monomeric MPs, a mutant reveals a higher stability than the wild type if the calculated solvation free energy indicates a favorable change. On the contrary, for oligomeric MPs the stability of a mutant increases as the solvation free energy of a mutated monomer becomes less favorable, indicating that the oligomeric MP mutant would be stabilized in solution due to the reduced desolvation cost for oligomerization. The present computational strategy is expected to find its way as a useful tool for assessing the relative stability of a mutant MP with respect to its wild type in solution.

Amino Acid Sequence↗

PubMed2004

Loop flexibility and solvent dynamics as determinants for the selective inhibition of cyclin-dependent kinase 4: comparative molecular dynamics simulation studies of CDK2 and CDK4.

The design and discovery of selective cyclin-dependent kinase 4 (CDK4) inhibitors have been actively pursued in order to develop therapeutic cancer treatments. By means of a consecutive computational protocol involving homology modeling, docking experiments, and molecular dynamics simulations, we examine the characteristic structural and dynamic properties that distinguish CDK4 from CDK2 in its complexation with selective inhibitors. The results for all three CDK4-selective inhibitors under investigation show that the large-amplitude motion of a disordered loop of CDK4 is damped out in the presence of the inhibitors whereas their binding in the CDK2 active site has little effect on the loop flexibility. It is also found that the binding preference of CDK4- selective inhibitors for CDK4 over CDK2 stems from the reduced solvent accessibility in the active site of the former due to the formation of a stable hydrogen-bond triad by the Asp99, Arg101, and Thr102 side chains at the top of the active-site gorge. Besides the differences in loop flexibility and solvent accessibility, the dynamic stabilities of the hydrogen bonds between the inhibitors and the side chain of the lysine residue at the bottom of the active site also correlate well with the relative binding affinities of the inhibitors for the two CDKs. These results highlight the usefulness of this computational approach in evaluating the selectivity of a CDK inhibitor, and demonstrate the necessity of considering protein flexibility and solvent effects in designing new selective CDK4-selective inhibitors.

Amino Acid Sequence↗

PubMed2004

Homology modeling, force field design, and free energy simulation studies to optimize the activities of histone deacetylase inhibitors.

As an effort to develop therapeutics for cancer treatments, a number of effective histone deacetylase inhibitors with structural diversity have been discovered. To gain insight into optimizing the activity of an identified lead compound, a computational protocol sequentially involving homology modeling, docking experiments, molecular dynamics simulation, and free energy perturbation calculations was applied for rationalizing the relative activities of known histone deacetylase inhibitors. With the newly developed force field parameters for the coordination environment of the catalytic zinc ion in hand, the computational strategy proved to be successful in predicting the rank orders for 12 derivatives of three hydroxamate-based inhibitor scaffolds with indole amide, pyrrole, and sulfonamide moieties. The results showed that the free energy of an inhibitor in aqueous solution should be an important factor in determining the binding free energy. Hence, in order to enhance the inhibitory activity by adding or substituting a chemical group, the increased stabilization in solution due to the structural changes must be overcome by a stronger enzyme-inhibitor interaction. It was also found that to optimize inhibitor potency, the hydrophobic head of an inhibitor should be elongated or enlarged so that it can interact with Pro29 and His28 that are components of the flexible loop at the top of the active site.

Amino Acid Sequence↗

PubMed2003

Determination of the active site protonation state of beta-secretase from molecular dynamics simulation and docking experiment: implications for structure-based inhibitor design.

Memapsin 2 (BACE) is an aspartyl protease known as beta-secretase that acts on the production of the beta-amyloid peptide in the human brain, a key event in the pathogenesis of Alzheimer's disease. Although it is expected that the net charge of the catalytic Asp diad would be -1 as in other kinds of aspartyl proteases, the exact protonation states of Asp32 and Asp228 have not been known without ambiguity. Two independent molecular dynamics (MD) simulations of BACE in complex with the potent inhibitor OM99-2 are carried out to determine the preferred protonation state of the Asp diad in the context that is consistent with the previous X-ray crystal structure. The results show that a strong hydrogen bond between the inhibitor hydroxyl group and Asp228 can be maintained only when Asp32 is neutral and Asp228 is ionized. The preference of this protonation state is further supported from the energetic and structural features found in the docking experiment of a novel potent inhibitor with the BACE active site. Thus, both MD and docking studies suggest that the role of hydrogen bond acceptor for the hydroxyl and piperazine groups of the inhibitors should be played by Asp228 instead of Asp32. This may be a key piece of information for the structure-based design/discovery of new inhibitor drugs.

Amyloid Precursor Protein Secretases↗

PubMed2003

Molecular dynamics and quantum chemical studies on the catalytic mechanism of Delta5-3-ketosteroid isomerase: the catalytic diad versus the cooperative hydrogen bond mechanism.

To further understand Delta(5)-3-ketosteroid isomerase (KSI) catalysis, we carried out molecular dynamics (MD) simulations of the KSI dimer ligated with a substrate and reaction intermediate analogue and high level ab initio calculations on relevant enzymatic reaction models. Simulation of the enzyme-substrate complex dimer systems showed asymmetric dynamics between the two monomers, in which the hydrogen bond pattern between the substrate and active site residues in the first and the second subunits supported the cooperative hydrogen bond (CH) and the catalytic diad (CD) mechanisms, respectively. On the other hand, only the CH mechanism was supported in the MD simulation of the enzyme-intermediate complex dimer. From MP2/6-31+G**//RHF/6-31G** calculations, we found the kinetic barriers for the two reaction mechanisms were similar. The CH route afforded a greater stabilization to the enolate intermediate than did the CD counterpart. Thus, the present computational studies indicate that the CH mechanism would be favored over the CD one in the catalytic action of KSI. However, the latter could not be ruled out conclusively because of the explicit appearance of a CD configuration in the MD trajectories of the enzyme-substrate complex and because of the similar intrinsic activation barrier for the CH and CD mechanisms. The appearance of configurations that favor the CD pathway is rationalized in terms of a model in which the KSI-substrate complex does not have a strong preference for one hydrogen bonding pattern over another, while the KSI-intermediate complex favors a cooperative hydrogen bond pattern in order to stabilize the reaction intermediate. This hypothesis is supported by the ab initio calculations which indicate that the CH intermediate is more stable than the CD one by approximately 6.3 kcal/mol.

Catalysis↗