[Chimera-users] depict hydrophobicity surface in super large molecules in chimera

[Elaine Meng]

Hi Marta,
Two general choices:  use Chimera molmap surface or use ChimeraX, which does not have the molecular surface calculation problems.  Also ChimeraX calculates a molecular lipophilicity potential (MLP) that varies through space analogous to ESP instead of just using amino acid lookup values like Chimera.

The Chimera amino acid lookup values are shown in this table, kdHydrophobicity column.
<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/midas/hydrophob.html>

(1) in Chimera just color the “molmap” surface by hydrophobicity.  In this case it is two steps, though: first you have to color the atoms by amino acid hydrophobicity, and then use color zone to make the surface coloring match the nearby atom coloring.  Also be careful when you make the molmap surface that it is calculated only from protein atoms (not solvent, ligands, …).  Details of the two steps:

     (A) color atoms by hydrophobicity with Render by Attribute (menu: Tools… Depiction… Render by Attribute, and in that dialog choose to color atoms by residue attribute kdHydrophobicity) or “rangecolor” command, e.g.

rangecolor kdHydrophobicity min dodger blue 0 white max orange red #3

<http://www.rbvi.ucsf.edu/chimera/docs/ContributedSoftware/render/render.html#render>
<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/midas/rangecolor.html>

     (B) use Color Zone (menu: Tools… Volume Data… Color Zone) to make the molmap surface coloring match the atom coloring, or command “scolor zone” e.g. if molmap is #3.1 and atoms are #3:

scolor #3.1 zone #3&protein range 5

<http://www.rbvi.ucsf.edu/chimera/docs/ContributedSoftware/colorzone/colorzone.html>
<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/midas/scolor.html#zone>
 
(2) get ChimeraX <http://www.rbvi.ucsf.edu/chimerax/>, open your structure, show surface (e.g. command “surface”), and color by MLP (e.g. command “mlp”).
<http://rbvi.ucsf.edu/chimerax/docs/user/commands/mlp.html>

Alternatively in ChimeraX you can just color by the amino acid kdHydrophobicity values like in Chimera using this script provided in the ChimeraX User Guide as an example of a custom preset (just save the file *.cxc and then open it in ChimeraX to run it):
<http://rbvi.ucsf.edu/chimerax/docs/user/kyte-doolittle_hydrophobicity.cxc>

I hope this helps,
Elaine
-----
Elaine C. Meng, Ph.D.                       
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On Oct 13, 2019, at 7:09 AM, Marta Perez Illana <marta.perez at cnb.csic.es> wrote:
> 
> Hi all
> I was trying to analyze the hydrophobic surface of two very large structures ( 3 chainsx 900 aa each so 2.700aa). As expected the default surface calculation has failed. Normally for electrostatic potential what works for me is making a mol map (molmap  #3  4 gridSpacing  0.5) and then calling the pdb2pqr and apbs servers directly from chimera, which is very convenient.
> 
> However I cannot find an analogous way to make it with hydrophobicity... Since the surface fails for such big molecules, the straight forward way (present-3interactive surface hydrophobicity) does fail as well...
> 
> Then... is there any server than can be called from chimera, to get hydrophobicity as an attribute to be depicted? Or alternatively could you suggest any server that gives output hydrophobic column, compatible  to get it after to chimera attributes? Reading a bit I found that, not as electric fields, that can be computed for structures, hydrophobicity comes just for the sequence, without taking into account the neighbours and context...
> 
> P.D: I have managed to represent in other programs the hydrophobic surface, but I really want to make it in chimera, to make it more consistent and easy to organize myself...
> 
> Thanks a lot! and sorry if the question goes beyond Chimera...
> Marta