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Tool: Modeller Comparative

The Modeller Comparative modeling tool is an interface to the Modeller program running on a web service hosted by the UCSF RBVI. The command-line implementation is modeller comparative. See also: Rotamers, Build Structure

Comparative modeling (sometimes called “homology modeling”) generates theoretical models of a protein using one or more known related structures and a sequence alignment of the known and unknown structures. The protein chain to be modeled is the target, and a known atomic structure used for modeling is a template.

Modeller is developed by the Šali Lab, and its users should cite:

Comparative protein modelling by satisfaction of spatial restraints. Šali A, Blundell TL. J Mol Biol. 1993 Dec 5;234(3):779-815.

Modeller comparative modeling requires the following for each target chain:

  1. At least one template structure.

  2. A sequence alignment that includes the sequence of the target; other sequences may also be included. The sequence alignment and template structure(s) should be open in ChimeraX and the template(s) associated with sequence(s) in the alignment.

  3. A Modeller license key. Academic users can register free of charge to receive a license key. Commercial entities and government research labs, please see Modeller licensing.

Startup and Input

The Modeller Comparative tool can be opened from the Sequence section of the Tools menu and manipulated like other panels (more...). It is also implemented as the modeller comparative command.

One sequence alignment per target should be chosen (highlighted) in the top section of the dialog. Immediately below, for each chosen alignment, the name of the target sequence should be selected from the pull-down menu.

Basic settings:

Advanced settings:

Modeller Comparative settings including the license key are automatically saved in the preferences. Other than the license key, the remembered settings apply only to the GUI; the command defaults are not changed.

Clicking Cancel simply dismisses the dialog, whereas OK sends information to the web service and initiates the calculation.

Modeller Results

When results are returned, the new models are opened, listed in the Model Panel along with any other models present in ChimeraX, and automatically superimposed on the lowest-model-ID template structure with matchmaker. Scores for the comparative models are shown in a Modeller Results panel:

Clicking a row in the panel shows the corresponding comparative model and hides the others. Clicking elsewhere in the panel shows all of the comparative models at once. Clicking a column header sorts on the values in that column.

The panel's context menu includes an option to Fetch Additional Scores using the SaliLab Model Evaluation Server:

The same Modeller license key as needed for comparative modeling is also required by the evaluation server, but it does not need to be specified again. Fetching additional scores is also implemented as the command modeller scores.

After additional scores have been fetched, the context menu option changes to Refresh Scores to allow re-evaluation after models have been modified (for example, to delete untemplated regions built as extended tails). However, since re-evaluation does not use all of the same information as does scoring during the original modeling process, it may worsen pre-existing GA341 and zDOPE scores and should only be used after making modifications that are expected to improve the scores.

UCSF Resource for Biocomputing, Visualization, and Informatics / August 2020