[Chimera-users] Values on electrostatic map at mouse locations (in surface-colour-options)

Elaine Meng meng at cgl.ucsf.edu
Mon Feb 5 10:04:48 PST 2018


Other than ESP calculation parameters, my only other idea is to make sure your map is correctly aligned with the surface.  If the map is rotated or translated relative to the displayed surface, that would be another way that the surface vertices could come too close to the near-singularities at atom centers (point charges) within the map.
Best,
Elaine

> On Feb 4, 2018, at 12:57 PM, Boaz Shaanan <bshaanan at bgu.ac.il> wrote:
> 
> Hi Elaine,
> Thanks a lot for your prompt reply and suggestions. I use the default surface offset of 1.4 A.
> I'll look into your other suggestions on the calculation of the potenial.
> The protein is halophilic and hence extremely negative overall with positive patch in the putative dna binding site. 
> Playing with the calculation params is an important factor as you pointed out.
> 
> Best regards,
> Boaz
> 
> Boaz Shaanan, Ph.D.
> Dept. of Life Sciences
> Ben Gurion University
> 
> 
> 
> 
> On Sun, Feb 4, 2018 at 8:36 PM +0200, "Elaine Meng" <meng at cgl.ucsf.edu> wrote:
> 
> Hi Boaz,
> For the most reasonable values, make sure that when you color by electrostatic potential, you use the “Surface offset” (default 1.4 Angstroms) to color the solvent-excluded surface by values measured some distance outside the surface.  The default distance is a “water” probe radius, approximating the location of the solvent-accessible surface. 
> 
> The (displayed) solvent-excluded surface is about that much closer to the atomic centers, the locations of the point charges used to calculate the ESP, than the solvent-accessible surface (not displayed).
> 
> Another potential foible is using some all-atom charge model on a structure that doesn’t have any hydrogens, so the whole thing is overwhelmingly negative.  However, if you are also seeing large magnitudes on positive regions, that probably isn’t an issue for you.
> I hope this helps,
> Elaine
> -----
> Elaine C. Meng, Ph.D.                       
> UCSF Chimera(X) team
> Department of Pharmaceutical Chemistry
> University of California, San Francisco
> 
> > On Feb 3, 2018, at 3:26 PM, Boaz Shaanan 
>  wrote:
> > 
> > Hi,
> > I'm seeing some weird values when I use this option, for example high +ve value when touching a very red area or -ve on a very blue area ( I use 3 colours scheme). I'm running linux alpha version v. 1.13 (build 41653) from 5 Jan 2018. The electrostatic potential was calculated in delphi. I have a vague recollection that this feature behaved more reasonably in the past when I used it (I could of course be wrong).
> > Thanks for your help.
> >         Boaz




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