Thank you Eric for your very detailed answers to my several questions. It will take me a few days to work through the suggestions. If I have any more troubles, I will contact you next week. Thanks very much, Roberta King ******************************** Roberta S. King, Ph.D. Department of Biomedical and Pharmaceutical Sciences College of Pharmacy University of Rhode Island http://www.uri.edu/pharmacy/faculty/king _____ From: Eric Pettersen [mailto:pett@cgl.ucsf.edu] Sent: Tuesday, April 03, 2007 7:57 PM To: Roberta King Cc: Chimera BB Subject: Re: [Chimera-users] viewing & comparison of multiple overlay structures On Apr 3, 2007, at 1:47 PM, Roberta King wrote: First, After overlaying multiple protein (pdb) structures with ligands using MultiAlign based on alignment, how does one easily view only the overlaid ligands? [Note: I have up to 36 structures overlaid, each with 0-2 ligands.] Hi Roberta, Using the command line (Favorites->Command Line), typing "~disp; show ligand" will hide all structures and then show only the ligands. If every structure had a ligand you would only need "show ligand" since the show command hides parts of structures that aren't to be shown, but if no part of a structure matches the show criteria, the structure isn't changed -- so you need the "~disp" also to guarantee that ligand-less structures get hidden. This is also doable with the menus by Select->Structure->ligand followed by Select->Invert Selection (or shift-right-arrow instead to invert the selection in all models) and then Actions->Atoms/Bonds->hide. From there, you will probably want to select the ligand clump by control dragging the mouse across the clump (there will be a green box outline as you drag the mouse) and then use Actions->Focus to zoom in on the clump and make it the center of rotation. Secondly, can chimera then calculate a solvent-accessible closed surface for the protein cavity surrounding each ligand? Alternatively, I could calculate the cavity first, then overlay based on alignment. The goal is to view the overlaid cavities for visual comparison. It depends. If the cavity is actually completely enclosed then Chimera won't depict it. If there is some channel to the binding pocket, then it should be depicted. I say "should" because the surfacing library we are currently using (MSMS) is known to have problems when there are narrow channels in a surface. We are working on a replacement library that should solve both these problems, but it's not ready yet. Providing that MSMS doesn't fail, your pockets should be depicted. It is also sometimes possible to work around the MSMS problem by adding hydrogens to a structure or by slightly changing VDW radii (with the vdwdefine command) -- but you have to do this before any surfaces fail because after a failure surfacing won't work again until you restart Chimera. You create a surface with Actions->Surface->show or the "surf" command. If with experience you know that surfacing certain models is problematic, you can restrict the surfacing to particular models by selecting them before using the menus or providing the model numbers as arguments to the surf command (e.g. "surf #0,3-7,9"). Thirdly, can chimera calculate electrostatic charge on amino acids surrounding a binding cavity and reflect that charge onto the closed cavity surface? Can this surface be included in overlay view? You can use the Add Charge tool (in the Structure Editing category) to add partial charges to all atoms. You can then use the Render By Attribute tool (Structure Analysis category) to color the surface and/or atoms based on the partial charges. For more precise electrostatics, you can use an external tool such as APBS or Delphi to generate an electrostatic grid, and open that in Chimera and then use the Electrostatic Surface Coloring tool (Surface/Binding Analysis category) to color the surface with the grid data. You can certainly show the surface(s) with the ligands overlaid. You would probably only want to show a few surfaces at most simultaneously for understandability (see next answer). Given the number of structures, I would much appreciate any advice on how to make this manageable. If Chimera cannot do the calculations, can it import multiple structures saved by another capable software, then overlay them using MultiAlign (including the surfaces)? Depending on the speed of your computer, its amount of memory and its graphics card, working with 36 structures and their surfaces at once may or may not be satisfactory (and unless you have a real high-end machine my guess would be not). You will want to use the Model Panel (under Favorites) to control which surfaces/structures are being shown -- particularly which surfaces since I imagine that looking at more than a few would be incredibly confusing. Another thing that will help is to delete parts of structures that you aren't interested in. One trick here is to use MultAlign Viewer to select one residue in each structure (create a region by mouse dragging that covers one column in the alignment -- those residues will be selected), then select the corresponding chains by clicking into the main window and hitting the up-arrow key, then right-arrow to invert the selection, and finally Actions->Atoms/Bonds->delete to delete all atoms that are not part of chains in the alignment. Hopefully your ligands will have the same chain ID as the chain in the alignment and therefore will not be deleted. You might want to look at your ligands after you've inverted the selection and make sure none are selected for the following deletion. If some are selected, deselect them with "~select ligand". As a quasi-extreme measure you could prune away parts of the structure more than a certain distance from the ligands. Select the ligand clump and use Select->Zone... to select residues further than a certain distance from the clump and then delete the selected residues. --Eric Eric Pettersen UCSF Computer Graphics Lab pett@cgl.ucsf.edu http://www.cgl.ucsf.edu