iview: an interactive WebGL visualizer for protein-ligand complex
© Li et al.; licensee BioMed Central Ltd. 2014
Received: 23 November 2013
Accepted: 18 February 2014
Published: 25 February 2014
Visualization of protein-ligand complex plays an important role in elaborating protein-ligand interactions and aiding novel drug design. Most existing web visualizers either rely on slow software rendering, or lack virtual reality support. The vital feature of macromolecular surface construction is also unavailable.
We have developed iview, an easy-to-use interactive WebGL visualizer of protein-ligand complex. It exploits hardware acceleration rather than software rendering. It features three special effects in virtual reality settings, namely anaglyph, parallax barrier and oculus rift, resulting in visually appealing identification of intermolecular interactions. It supports four surface representations including Van der Waals surface, solvent excluded surface, solvent accessible surface and molecular surface. Moreover, based on the feature-rich version of iview, we have also developed a neat and tailor-made version specifically for our istar web platform for protein-ligand docking purpose. This demonstrates the excellent portability of iview.
Using innovative 3D techniques, we provide a user friendly visualizer that is not intended to compete with professional visualizers, but to enable easy accessibility and platform independence.
KeywordsStructural bioinformatics Visualization Molecular docking
Visualization of protein-ligand complex plays an important role in elaborating protein-ligand interactions and aiding novel drug design. To date, dozens of visualization tools already exist. VMD , PyMOL (http://www.pymol.org) and Chimera  are very well-known and highly cited. They can interpret multiple file formats and generate multiple representations to supply precise and powerful control. AutoDockTools4  provides native support for the PDBQT file format, which is widely used in various protein-ligand docking software such as AutoDock , AutoDock Vina , and our idock . We also developed our own method  to visualize structures in virtual reality settings and employ fragment-based de novo ligand design strategy for interactive drug design. PoseView  and LigPlot+ , on the other hand, plot 2D diagrams of protein-ligand interactions from 3D coordinates.
Full features of iview
File format input
protein secondary structure
ball & stick
cylinder & plate
C alpha trace
B factor tube
Van der Waals surface
solvent excluded surface
solvent accessible surface
Proteins surface opacity
Protein surface wireframe
Atom and residue labeling
Virtual reality effect
iview is refactored from GLmol 0.47, using three.js as its primary 3D engine with antialiasing support. It is based on WebGL canvas and can be easily integrated into existing HTML5 web pages to display molecular models without requiring Java or browser plugins. It loads a protein-ligand structure from the PDB (Protein Data Bank)  as its data source via a RESTful interface. It renders four standard representations of primary structure, namely line, stick, ball & stick and sphere, and five standard representations of secondary structure, namely ribbon, strand, cylinder & plate, C alpha trace and B factor tube. It colors the structure by either atom spectrum, protein chain, protein secondary structure, B factor, residue name, residue polarity, or atom type, by setting the vertex colors of the geometry object of the corresponding representation. It supports user interactions including rotation, translation, zooming and slab with mouse or hand touch manipulation. It provides both perspective and orthographic cameras, and anaglyph, parallax barrier and oculus rift effects from three.js examples for use in a virtual reality environment.
It is worthwhile to highlight that iview performs all parsing and rendering in the client browser, without any dependency on server side at all, ensuring the data privacy is maintained. This is unlike ChemDoodle Web Components, some of whose functions send data to a dedicated server for processing and wait for retrieval of results.
The differences between iview and GLmol are listed in the Additional file 1.
We take as example the CCR5 chemokine receptor-HIV entry inhibitor maraviroc complex  (PDB code: 4MBS).
We have successfully tested iview in Chrome 30, Firefox 25, Safari 6.1 and Opera 17. Support for IE 11 is experimental because gl_FrontFacing is unsupported in IE 11. Refer to http://caniuse.com/webgl, for compatibility of WebGL support in desktop and mobile browsers.
We emphasize portability and usability, and illustrate that iview can be easily modified to suit one’s particular application, given that iview is free and open source under a permissive license. We take protein-ligand docking as an example. Based on the feature-rich version of iview, our tailor-made version specifically for idock jobs cleans up many dispensable functions, enabling a very neat interface. It only retains the rendering of primary structure of protein and ligand, and the construction of protein surface. Most importantly, it implements new features especially for protein-ligand docking purpose.
In the input phase of a docking job, it merely requires a PDB file, which can be obtained either from the PDB database  or via homology modeling, and then constructs the protein surface asynchronously in a separate web worker to keep the web page responsive. It automatically detects a binding site from the largest co-crystallized ligand first by finding the smallest cubic box that covers the entire ligand and then by extending the box by 50% in all the three dimensions in order to reserve space for conformational sampling. In case of non-existence of co-crystallized ligand, the binding site is defaulted to the geometric center of the protein. The binding site is visually depicted in the form of a cubic box whose center and size can be manually adjusted by users in real time.
We have designed and developed iview to be a simple and straightforward way to visualize protein-ligand complex. It enables non-experts to quickly elucidate protein-ligand interactions in a 3D manner. Furthermore, iview is free and open source, and can be easily integrated into any bioinformatics application that requires interactive protein-ligand visualization.
Availability and requirements
Project name: iview
Project home page: http://istar.cse.cuhk.edu.hk/iview
Operating system: Platform independent
Other requirements: Browser and graphics card with WebGL capability
License: Apache License 2.0
Takanori Nakane thanks Japan Society for the Promotion of Science (JSPS) for scholarship (DC1). This work was partly supported by Grant-in-Aid for JSPS Fellows (Grant Number 11J04341).
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