IC_residue's get_angle function gives different results for psi and "N:CA:C:1N" #5113
Description
I am evaluating the angles of the Cif-file https://www.rcsb.org/structure/3BN9 , downloaded in PDBx/mmCIF format.
For chain F, residue 82 I get different values depending on if I evaluate with "N:CA:C:1N" or "psi", despite documentation stating they should be the same.
The exact code is
for res in chain.get_residues():
if res.id[0] != " ":
continue # water or external residue
ic_res = res.internal_coord
if ic_res:
angle_res = ic_res.get_angle(angle_key=angle)
where angle is either "psi" or "N:CA:C:1N". "N:CA:C:1N" gives a None-value, while psi gives around 122 degrees. The chain is BioPython's chain object for chain F.
Having debugged, it seems like the two methods define the 1N atom differently, which probably causes the problem, but I could not figure out which was correct. As I understand it, these two should always be the same, so I hope someone can explain why they are different, or fix the issue if there is a glitch.