Hello Hong, you can limit the contacts calculation to only include histidine residues, or specific atoms in histidine residues (e.g. if you only cared about the sidechain nitrogens, or only the alpha-carbons). Example: contacts :his@nd1,ne2 restrict :his@nd1,ne2 distanceOnly 500 log true ...(plus any other options you wanted) to list all-by-all distances <500 Angstroms between histidine sidechain nitrogens in the Log. I hope this helps, Elaine ----- Elaine C. Meng, Ph.D. UCSF Chimera(X) team Department of Pharmaceutical Chemistry University of California, San Francisco

On Apr 5, 2022, at 9:20 AM, HONG ZHAN via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:

Dear all,

I am interested to get a list of distances between histidine residues in my built model. Because I would like to see which crosslinker can potentially help to maintain the structure better during purification.

I have noticed that I can measure one residue in chain A to all other atoms in chain B using contact function, however, I want to get a list of distances between any histidine imidazole (neighboring distance), is there a way to do that in ChimeraX?

Super thanks in advance.

Best, Hong