Build/edit a query using the Wizard

Background information

This tutorial teaches the user to create a new query to either save or to use in ROCS. The wizard creates a query through one of a few predesigned paths.

You have recently been assigned to a trypsin inhibitor project. You are interested in building a query from known ligands in their binding modes, suitable for use in ROCS for vHTS. A set of 19 trypsin inhibitors are available as co-crystal structures from the PDB (see the IDs for trypsin inhibitors in the [PDB-IDs] citation). The dataset has been prepared by aligning the 19 protein crystal structures. The ligands were then extracted to give a set of 19 ligands, aligned in the protein binding pocket frame of reference. The query building wizard will be used to construct a ROCS query to employ only the ligands that are most representative of the set as a whole.

The tutorial will require approximately 10 minutes to complete.

Build models using the wizard

Open a new ROCS session. At the Welcome screen select the option to Create a query with a wizard. This will open up the Create a query dialog.

In the top tab, Create Query, select the radio button for Ligand Model Builder and then click Next.

In the Load Aligned Ligands tab click on the Filename area and browse to the file containing the 19 aligned trypsin ligands. This file is located in the OPENEYE_DIR/data/vrocs/wizard directory and is called pdbmodel_ligands.oeb.gz. Click OK in the file browser to accept the choice of file. The file will be loaded and the first ligand is displayed in the preview. Examine the ligand by rotating (left mouse button) or zooming (mouse wheel) the structure image. Scroll through the list of ligands using the green arrows. When satisfied click Next to continue.

It is not required to change any of the options in the Adjust Parameters tab, as indicated by the green check mark next to the tab name. However, for the purposes of this tutorial we will keep the Max Molecules Per Model as 3 (consider only models containing 1,2 or 3 molecules) but increase the Models to Keep to 3 (keep the best 3 models for further review). Enter Trypsin in the Prefix field and check the box to Merge Color Atoms.

Click Next to begin building the models. A progress dialog will provide information on the model building. When all the 1159 models containing 1, 2 or 3 molecules from the dataset of 19 trypsin inhibitors have been built and compared the top 3 models are listed in the Pick Queries dialog.

Visualize the results

The first model in the list, ‘Trypsin 1’, is displayed in the preview window and is made from three of the ligands: 1G3E.pdb, 1GHZ.pdb and 1QB6.pdb. This is the model that is most representative of the dataset of 19 inhibitors as a whole.

Note that the three ligands align at one end of the model whilst the other end is described by only the single, larger molecule. Where the three ligands align closely the donor/cation/donor triad of color atoms have been merged to a single representation, instead of close color atoms from each ligand (e.g. three partially overlaid cation color atoms). Retaining multiple instances of the color atoms would serve to stress the importance of these features in the model over the other features.

Click on the second model, ‘Trypsin 2’. Its name will be highlighted in blue and it will be displayed in the preview window. This is the second most preferred model and is also made of three ligands: 1H4W.pdb, 1K1I.pdb and 1QB9.pdb. Note that this is a different set of three ligands than Trypsin 1 (although it is possible for some ligands to be used in multiple high ranking models).

The third model, ‘Trypsin 3’ is made of 1C5T.pdb, 1GJ6.pdb and 1QBO.pdb. All three models contain one of the larger, hinged ligands and at least one of the set of smaller ligands.

Save the results

Place a check mark next to the name of each model to select it for export to the main vROCS interface. In this tutorial we will export all three models and save them so they can be used in further validation experiments. However, in your own work you may choose only some of the models for export.

Having checked all three models click Finish to close the Build a new query dialog. Model ‘Trypsin 1’ will be displayed in the main vROCS 3D window and the Welcome panel is to the left of the screen. In the Welcome panel click on Perform a simple ROCS run. The three models are listed as potential queries in the Inputs dialog, with ‘Trypsin 1’ as the active query. To save ‘Trypsin 1’ as a ROCS saved query (*.sq) file select File > Save Query As… from the main File menu. Navigate to your preferred working directory and enter Trypisn_1.sq as the file name. Click OK to save the file. In the query list select model ‘Trypsin 2’ and use File > Save Query As… to save this query as Trypsin_2.sq. Repeat with model ‘Trypsin 3’ to save a query with filename Trypsin_3.sq.

Conclusions

This concludes the tutorial “Build/edit a query using the Query Wizard”. In this tutorial we used a set of 19 aligned known trypsin ligands and built three potential ROCS queries, using up to three of the ligands from the dataset. These queries best describe the dataset as a whole, based on TanimotoCombo scores of all the potential models. These models can be further validated before use, as described in the tutorial Perform a **ROCS** validation run.

If you have time some suggestions for further study are:

• Try changing some of the model building parameters. (Note, it is recommended to keep the maximum number of molecules in a model low (less than or equal to five), to avoid extended run times for model building and overly complex output models/ROCS queries.

• Modify the current force field in the Preferences dialog (Edit > Preferences, vROCS tab) and see whether this changes the models

• Re-run the tutorial steps with your own set of aligned ligands