Chain IDs not written consistently

[Tristan Croll]

The following bug report has been submitted:
Platform:        Windows-10-10.0.19041
ChimeraX Version: 1.3rc202110222254 (2021-10-22 22:54:52 UTC)
Description
The attached file was saved from ChimeraX 1.2 (if I recall correctly) back in July or August, with 2-character chain IDs for everything other than a few wayward waters and detergents (the chain IDs were assigned within ChimeraX). Would have saved as mmCIF, but my collaborator still isn't comfortable with that format. Anyway, on reopening some (but not all) residues have the first character of the chain ID appended to their names, with their chain IDs being the second character of the "true" chain ID. Looking at the PDB file, here's what I think is happening:

- on writing to PDB, residues with two-character residue names *and* two-character chain IDs (in this case MG) are written incorrectly, with the first character of the chain ID becoming the last character of the residue name, e.g.:

HETATM 1978 MG   BCLBH1602     102.222 111.454 119.211  1.00  5.22          Mg
HETATM 1979 MG   MGB H1603      95.040 112.034 108.240  1.00 14.21          Mg
HETATM 1980  O   HOHBH1608      99.357 108.094 151.167  1.00 20.80           O

- on reading, once the parser hits the erroneously-written residue and treats it as residue MGB 1603 of chain H, all residues from the same chain beyond that point are interpreted as 4-character residues from chain H.

So I guess the real bug here is in the writer rather than the parser - but I also think it's a bad idea for the parser to be "mixing and matching" like this. Would be better if a given file is interpreted as *either* hybrid-36 or 4-character residues, not both.


OpenGL version: 3.3.0 NVIDIA 471.11
OpenGL renderer: NVIDIA GeForce RTX 2080/PCIe/SSE2
OpenGL vendor: NVIDIA Corporation
Manufacturer: Notebook                        
Model: P7xxTM1
OS: Microsoft Windows 10 Education (Build 19041)
Memory: 68,654,501,888
MaxProcessMemory: 137,438,953,344
CPU: 16 Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz
OSLanguage: en-GB
Locale: ('en_GB', 'cp1252')
PyQt5 5.15.2, Qt 5.15.2
Installed Packages:
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File attachment: chains_renamed.pdb

chains_renamed.pdb​

[Tristan Croll]

Added by email2trac

[Eric Pettersen]

The code to put spaces around short residue names was wrong. Not strongly inclined to change the parser. Currently it makes the chain ID call on a chain-by-chain basis, which simplifies the already complex parsing code. I prefer just to fix the writer for now.