Eric,

Thank you very much for your helpful suggestion. After removing all the disulfide bonds in that chain, I was able to modify the φ/ψ angles successfully. Your advice saved me a lot of time and allowed me to accomplish my goal. I truly appreciate your help.

Best,

Zhen

From: Eric Pettersen <pett@cgl.ucsf.edu>
Date: Wednesday, October 15, 2025 at 15:03
To: Gong, Zhen <zg2234@cumc.columbia.edu>
Cc: chimerax-users@cgl.ucsf.edu <chimerax-users@cgl.ucsf.edu>
Subject: [EXTERNAL] Re: [chimerax-users] Problems adjusting the phi/psi angles with ChimeraX

Hi Zhen,

This probably means that the bond is part of a large cycle of bonds created by cross-chain linkages such as disulphide bonds.  You would have to break one or more of those linkages in order to rotate the bond.

--Eric

Eric Pettersen

UCSF Computer Graphics Lab

On Oct 15, 2025, at 10:54 AM, Gong, Zhen via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:

Dear ChimeraX team,

I was trying to use ChimeraX to change the phi/psi angles of a residue in the loop region but encoured this error: ILE 411 N ↔ CA is part of a ring/cycle and cannot be rotated. There is no ring/cycle in ILE411 or neibouring residues: ASN 410 or THR 412.

I tried ChimeraX daily (version 1.10.dev202504260127 (2025-04-26) and ChimeraX 1.10.1 but the same error happened. I am wondering if it is possible to change the phi/psi angles with ChimeraX. Thank you.

Best,

Zhen

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