[Chimera-users] Electrostatic potential values at each residue

Elaine Meng meng at cgl.ucsf.edu
Wed Dec 4 09:37:29 PST 2013

Dear TM,
The values are for different locations:  the attributes are values mapped to atomic centers, whereas the surface coloring shows the potential values farther out, at the surface or beyond (even farther from the atom centers).  By default in Chimera, Coulombic or other electrostatic surface coloring shows the values at points 1.4 angstroms outward from the displayed (solvent-excluded) surface, approximating the values at the larger solvent-accessible surface, which is not displayed.  This is the "Distance from surface" parameter in the Coulombic surface coloring dialog, and there is a similar option in the Surface Color tool.

Using the Coulombic coloring tool does not automatically create attributes.  I'm guessing you used the option to create a grid, then read in the grid, and then used Values at Atom Positions to get the attributes assigned. (Your session cannot be restored because it also requires the grid file.)

To summarize, however, you would not expect the values to be the same because the locations where the potential is evaluated are quite different.

I hope this helps,
Elaine C. Meng, Ph.D.                       
UCSF Computer Graphics Lab (Chimera team) and Babbitt Lab
Department of Pharmaceutical Chemistry
University of California, San Francisco

On Dec 2, 2013, at 6:31 PM, Tatsuhito Matsuo wrote:

> Dear All,
> I'd like to get the electrostatic potential (ESP) values at each residue in a protein. I implemented the "Coulombic Surface Coloring", then get the distribution of ESP values at each residue by "Render/Select by Attribute" (Attributes of [residues], Select -> Attribute [value_Coulombic_ESP]). However, The surface plot and the ESP values obtained by "Render/Select by Attribute" do not coincide with each other. For example, there are some residues where the surface plot reports positive ESP values, while "Render/Select by Attribute" gives negative ones (e.g. VAL70 CG2 in the Chimera session file attached.). Could you teach me how to solve this discrepancy?
> Thank you very much in advance,
> T.M.

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