annotate_sse() only works for single chains

[padix-key]

The circumstance that structure.annotate_sse() only annotates a single protein chain makes it usage more complicated for multimers. It would be convenient if the function could annotate multiple chains at once.

Furthermore, DSSPApp.annotate_sse() does not give the correct number of SSEs for a mult-chain structure. For example:

import biotite.structure as struc
import biotite.structure.io.mmtf as mmtf
import biotite.database.rcsb as rcsb
import biotite.application.dssp as dssp


mmtf_file = mmtf.MMTFFile.read(rcsb.fetch("1A3N", "mmtf", "."))
atoms = mmtf.get_structure(mmtf_file, model=1)
atoms = atoms[struc.filter_canonical_amino_acids(atoms)]
sse = dssp.DsspApp.annotate_sse(atoms)
assert len(sse) == struc.get_residue_count(atoms)

gives an AssertionError