2021 DOCK tutorial 2 with PDBID 2ZD1
This tutorial will allow the student to perform a virtual screen of a large number of ligands to a target through the use of molecular docking. The student will also learn how to visualize the starting ligand and receptor along with the resulting docked ligand poses.
The DOCKING program specifically computes the interaction energy between the receptor and candidate ligand at different orientations. The ligand with the highest activity (usually the ideal candidate for a synthetic ligand or drug) would have the lowest computed energy.
Docking algorithms can be broadly classified as flexible (anchor and grow) or rigid. A rigid docking algorithm begins with a fully-formed ligand (whose structure is obtained from experiment) and allows for sampling of the rigid placement of the given experimental pose in the binding site of the receptor while varying the translational and rotational degrees of freedom of the whole ligand within the three spatial dimensions. Internal angle rotational degrees of freedom are not explicitly sampled with basic rigid docking.
Traditional flexible docking starts with a ligand scaffold, which is usually the largest substructure in a ligand, identified as such after the molecule is divided into substructures at its rotatable bonds. By a chosen method, such as Monte Carlo sampling or simulated annealing, multiple poses of this “anchor” substructure are then generated within the receptor binding pocket and scored. The next substructure’s layers of atoms are then added to the most favorable subset of initial anchor poses, and the process repeats until all the molecule is fully rebuilt within the receptor. This on-the-fly flexible conformer growth and minimization process is known as “anchor and grow.”
'Conformal space search' A sequence of complexes of receptors and ligands in specific poses are constructed for subsequent evaluation by a set of scoring functions.
Tools and Platforms
Protein DataBank https://www.rcsb.org/structure/2zd1
DOCK 6.9 is one of the many tools available to computational biologists that predicts ligand binding geometries and interactions. The functions of DOCK 6.9 are diverse and have several general applications. A primary use of the program involves a virtual screening of thousands of molecules for an intended purpose. These purposes can include database screenings for molecules that inhibit enzyme activity, bind a particular protein, or even bind to larger complexes. As more versions of the program are released, new features are added such as the inclusion of solvation and receptor flexibility considerations in its calculations.
2ZD1 is the PDB code for the catalytic complex between human HMG-CoA reductase (HMGR) and Simvastatin. HMGR is considered a rate-controlling enzyme in the metabolic pathway responsible for the biosynthesis of cholesterol. Inhibitors of HMGR, known as statins, are often prescribed as treatment therapies for high cholesterol patients. While statins inhibit the catalytic effect of HMGR, they also provide other positive biochemical effects such as the stimulation of bone growth and anti-inflammatory responses. Studying statin binding using this complex can potentially aid in the discovery of drugs capable of producing these off-target effects.
File and Directory Preparation
Before begining the actual docking procedure, we will create a set of directories to store the various files we will be generating in an organized manner. We will also download the initial PDB file for our complex from the RCSB PDB.
Note: The nomenclature used below is not required but is recommended for most efficient use of the tutorial.
- Navigate to your personal student directory for AMS 536:
- Create a directory to store all files used and generated in this tutorial:
- Navigate into this new directory:
- Create all the directories for docking:
mkdir 01_structure 02_surface_spheres 03_gridbox 04_dock 05_virtual_screen 06_virtual_screen_mpi 07_cartesianmin 08_rescore
- Download the PDB file to a local directory
- Copy the PDB file to
scp or rsync
You can confirm the presence of these directories within 2ZD1 by using the "ls" command.
Receptor and Ligand Preparation
We will exract the individual receptor and ligand structure from our PDB file and add hydrogens and charges where appropriate.
We will verify that the protein structure downloaded from the PDB aligns with the description in the submitted experimental paper.
- Open the Chimera application
- Open the PDB file in Chimera:
file -> open, navigate to PDB file and select open
You should now be able to visualize the complex as shown below
- Begin to prepare the receptor by deleting all the non-receptor atoms. This also includes delete any chains in the receptor that are not of interest and or do not coordinate with the ligand.
Select -> Chain -> (Undesired chain) Actions -> Atoms/Bonds -> Delete.
Select -> Residue -> All-nonstandard Actions -> Atoms/Bonds -> Delete.
- Save the prepared receptor locally in .mol2 format.
File -> Save mol2... -> "2ZD1_rec_nH.mol2"
- Copy the mol2 file to
scp or rsync
Note that the file that we created does not contain any hydrogen atoms, we will now save a second receptor file with hydrogens and charge added to the molecule.
Select -> Chain -> (Undesired chain)
Actions -> Atoms/Bonds -> Delete.
Select -> Residue -> All-nonstandard
Actions -> Atoms/Bonds -> Delete.
File -> Save mol2... -> "2ZD1_rec_nH.mol2"using
Copy the mol2 file to <code> 01_structure
scp or rsync</ol>