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Showing posts with label Molecular Modeling. Show all posts
Showing posts with label Molecular Modeling. Show all posts

Monday, August 4, 2008

Web-Based Interface For Molecular Docking


Docking Server windows are organized into three modules following the basic steps of docking calculations:

(1) Protein set-up
(2) Ligand set-up
(3) Docking Calculation.

The user can create its own ligand, protein and dockings folder so that the ligands, proteins and dockings can be saved and organized for later use.

Protein set-up

The protein can be uploaded as a pdb file, or can directly be downloaded (after keyword search in the database if needed) from Protein Data Bank (www.rcsb.org). At this step the user can choose whether to include water molecules or any other heteroatoms present in the pdb file in the docking calculation. Add heteroatoms to my ligands command allows the adding of molecules present in the pdb files to the ligand folder. In the next step, the simulation box can be chosen. The simulation box can be either selected to cover only a known ligand binding site, or the whole target protein. Exact coordinates can be given as center of simula¬tion box similarly as in Autodock. In addition, Docking Server allows the user to define amino acids or heteroatoms present in the uploaded pdb file as center or borders of the simulation box.

Ligand set-up

The ligands can be uploaded or directly drawn. Besides single ligands, multiple ligands in sdf files can also be uploaded so that to enable high throughput docking of ligand libraries. The user can chose the desired pH affecting the protonation state of the ligand and whether semiempirical charges and optimization should be carried out during the process of ligand preparation.

Protein Ligand Docking

In the docking window the user can choose multiple ligands and/or dockings for the docking calculation. The docking calculation can be started using the default parameters; moreover, it is also possible to manually set docking parameters for more advanced users.

Finally, docking results are automatically processed in different ways to offer better understanding of the results:

1, resulting docking energies, frequencies and downloadable pdb coordinates are summarized in a table;
2, figures of the calculated ligand-protein complexes are automatically generated by VMD or can be manually rendered using the Jmol applet;
3, ligand-protein interaction tables are automatically generated that helps identify the driving forces of the complexation;
4, HB-plots (Bikadi, et al., 2007) are automatically generated to interpret the effects of the binding on the whole protein structure; 5, The applied methods and the according references are summarized.

Sunday, August 3, 2008

Molecular Docking Server


Analysis of the mode of interaction between ligands and their target proteins is of crucial importance in order to explore different aspects of biochemical processes. Besides laboratory experiments, there is an emerging role of in-silico methods in investigating the interactions of ligands to proteins.

In-silico study of protein-ligand interaction involves molecular docking, where the binding energy and geometry of ligands, substrates or possible drug candidates to target proteins is predicted using computational chemistry methods.

The task in molecular docking assignments is to find the best ligand protein complex geometry. The problem is usually seen as an optimization task where the goal is to minimize the intermolecular interaction energy between the two molecules of interest. Since the possible number of ligand- protein complex geometry is usually very large, different algorithms are used in order to accurately explore the space of possible conformations while decreasing the computational power needed for the docking calculation at the same time.

Thus, a molecular docking calculation consists of the following steps:

(1) Optimization of the ligand geometry, calculate pH-dependent partial charges, identify rotatable bonds and

(2) Calculate electrostatic properties of the protein of interest and define the ligand-binding region,

(3) The ligand-protein interaction is then calculated by a scoring function that includes terms and equations that describe the intermolecular energies. The result of a docking calculation is a ligand-protein complex geometry and the corresponding binding energy. Therefore, for accurate interpretation of the results, a high-quality representation of the complex geometry is of great importance as well

(4)DockingServer integrates a number of computational chemistry software specifically aimed at correctly calculating parameters needed at different steps of the docking procedure, i.e. accurate ligand geometry optimization, energy minimization, charge calculation, docking calculation and protein-ligand complex representation.

Thus, the use of DockingServer allows the user to carry out highly efficient and robust docking calculation, which could not be achieved using single software so far. Since the calculations run on our servers, the use of DockingServer does not require powerful hardware or pre-installed software from the user.

The core of DockingServer web application is our integrating PHP software connected to a MySQL database, where the different tasks are automatically managed by daemons running on our servers and the input data will be read from the database and output data will be directed into the database.

The AutoGrid/AutoDock 4.0 (Morris, et al., 1998) program package is used for docking calculations, allowing docking of flexible ligands to proteins. With the help of Autodock program package the partial charges and atom types of the ligand and proteins can be assigned. However, the results of docking calculations strongly depend on the accuracy of charges calculated in the ligand.

Thus, besides offering ligand partial charge calculation with the Auto-Dock program package DockingServer also integrates calculator plug-ins from Chemaxon (Csizmadia, 2000) and the MOPAC2007 program (Stewart, 2007) for accurate pH-dependent protonation and ligand partial charge calculation. Moreover, geometry optimization, refinement of the ligand geometry using semiempirical methods (PM6) can be carried out. Automatic conversions between necessary file formats are achieved by Chemaxon tools.