Dear Patrick, I can't answer the Python question, but I recommend using the Ribbon Style Editor (under Tools... Depiction) to do this instead of changing code. <http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/ribbonstyle/ ribbonstyle.html> In Ribbon Style Editor, see the "Residue Class" section. Instead of changing the Chimera defaults for amino acids and nucleotides, you can make your own new classes, name them, and apply them selectively by name. The documentation also explains more about how ribbon guide and orientation atoms are used: <http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/ribbonstyle/ ribbonstyle.html#class> I believe you cannot use the same atom as both guide and orientation atom. That may be the problem in your case, since the default peptide orientation atom is O. You may want to try some different combinations of which backbone atoms are used as guide and orientation. Some previous posts about ribbon residue class: <http://www.cgl.ucsf.edu/pipermail/chimera-users/2008-July/002809.html> <http://www.cgl.ucsf.edu/pipermail/chimera-users/2007-October/ 001931.html> I hope this helps, Elaine ----- Elaine C. Meng, Ph.D. meng@cgl.ucsf.edu UCSF Computer Graphics Lab (Chimera team) and Babbitt Lab Department of Pharmaceutical Chemistry University of California, San Francisco http://www.cgl.ucsf.edu/home/meng/index.html On Oct 17, 2008, at 3:50 AM, Patrick Ladam wrote:

Hello list,

I'd like to change the guide atom in res.ribbonData to use O instead of CA as an example. Here is what I did:

for r in mol.residues: for a in r.atoms: if a.name == 'O': r.ribbonData.guide = a # Set O as guide Atom if r.isHelix: # Update the display r.ribbonDisplay = True r.ribbonDrawMode = chimera.Residue.Ribbon_Round

This does not seem to redisplay/recompute the helix through O Atoms.

I am not confident with the way I altered the guide Atom or is it another problem like updating the ribbon or so... If someone can help...

Thanks to all PL