Retain chain and residue numbering in RFdiffusion (#348)
A number of issues (e.g., #103 , #171 ,
https://github.com/RosettaCommons/RFdiffusion/issues/312 , #315 ) have
mentioned that RFdiffusion will change the chain IDs and residue
numbering of the input structure. The designed chain ends up as chain
"A", and the fixed chain(s) end up as chain "B". The numbering is also
reset to start at 1. This can be particularly problematic in cases where
comparisons to structures are needed, as well as multi-chain situations
where all of the chains get fused.
Inspired by @GCS-ZHN 's comment and solution referenced in Issue #103 ,
I've modified the code to maintain chain and residue numbering. In
particular:
Chains that are not "designable" will retain their original chain ID
letters and residue numbers.
Chains that are partially fixed (e.g., motif re-scaffolding) will retain
their original chain ID letters. Residues will be re-numbered from 1 to
length of chain. (It was not clear to me what the "correct" behaviour of
chain residue numbering should be, given that the length of the chain
and the position of any fixed residues might change.)
Chains that are being fully generated de novo will be assigned the first
available chain ID in the alphabet not used by any other chain. Residues
will be numbered from 1 to length of chain.