After refining structures from crystallographic diffractions or cryo-EM data, yet these PDB files don’t have pre-defined structural structure regions. I sometimes found ChimeraX doesn’t display same helices or sheets as PyMOL or Coot does.

In ChimeraX, if we are certain of the secondary structural regions, a simple command called “setattr” lets users manually define helices or sheets, like PyMOL’s “alter”.

Here is a good and short explanation provided by ChimeraX team.

argument: setattr res ss_type 0

examples:

setattr :10-30, 50-56, 90-94 res ss_type 1 (define helices)

setattr /B:23-30 res ss_type 2 (Define B chain, aa 23-30 as sheet)

The ss_type is numerical :

0 = coil

1 = helix

2 = sheet

*update title on Aug. 9. (was wrong title)