Bio.PDB.Polypeptide module¶
Polypeptide-related classes (construction and representation).
Simple example with multiple chains,
>>> from Bio.PDB.PDBParser import PDBParser
>>> from Bio.PDB.Polypeptide import PPBuilder
>>> structure = PDBParser().get_structure('2BEG', 'PDB/2BEG.pdb')
>>> ppb=PPBuilder()
>>> for pp in ppb.build_peptides(structure):
... print(pp.get_sequence())
LVFFAEDVGSNKGAIIGLMVGGVVIA
LVFFAEDVGSNKGAIIGLMVGGVVIA
LVFFAEDVGSNKGAIIGLMVGGVVIA
LVFFAEDVGSNKGAIIGLMVGGVVIA
LVFFAEDVGSNKGAIIGLMVGGVVIA
Example with non-standard amino acids using HETATM lines in the PDB file, in this case selenomethionine (MSE):
>>> from Bio.PDB.PDBParser import PDBParser
>>> from Bio.PDB.Polypeptide import PPBuilder
>>> structure = PDBParser().get_structure('1A8O', 'PDB/1A8O.pdb')
>>> ppb=PPBuilder()
>>> for pp in ppb.build_peptides(structure):
... print(pp.get_sequence())
DIRQGPKEPFRDYVDRFYKTLRAEQASQEVKNW
TETLLVQNANPDCKTILKALGPGATLEE
TACQG
If you want to, you can include non-standard amino acids in the peptides:
>>> for pp in ppb.build_peptides(structure, aa_only=False):
... print(pp.get_sequence())
... print("%s %s" % (pp.get_sequence()[0], pp[0].get_resname()))
... print("%s %s" % (pp.get_sequence()[-7], pp[-7].get_resname()))
... print("%s %s" % (pp.get_sequence()[-6], pp[-6].get_resname()))
MDIRQGPKEPFRDYVDRFYKTLRAEQASQEVKNWMTETLLVQNANPDCKTILKALGPGATLEEMMTACQG
M MSE
M MSE
M MSE
In this case the selenomethionines (the first and also seventh and sixth from last residues) have been shown as M (methionine) by the get_sequence method.
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Bio.PDB.Polypeptide.index_to_one(index)¶ Index to corresponding one letter amino acid name.
>>> index_to_one(0) 'A' >>> index_to_one(19) 'Y'
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Bio.PDB.Polypeptide.one_to_index(s)¶ One letter code to index.
>>> one_to_index('A') 0 >>> one_to_index('Y') 19
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Bio.PDB.Polypeptide.index_to_three(i)¶ Index to corresponding three letter amino acid name.
>>> index_to_three(0) 'ALA' >>> index_to_three(19) 'TYR'
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Bio.PDB.Polypeptide.three_to_index(s)¶ Three letter code to index.
>>> three_to_index('ALA') 0 >>> three_to_index('TYR') 19
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Bio.PDB.Polypeptide.three_to_one(s)¶ Three letter code to one letter code.
>>> three_to_one('ALA') 'A' >>> three_to_one('TYR') 'Y'
For non-standard amino acids, you get a KeyError:
>>> three_to_one('MSE') Traceback (most recent call last): ... KeyError: 'MSE'
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Bio.PDB.Polypeptide.one_to_three(s)¶ One letter code to three letter code.
>>> one_to_three('A') 'ALA' >>> one_to_three('Y') 'TYR'
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Bio.PDB.Polypeptide.is_aa(residue, standard=False)¶ Return True if residue object/string is an amino acid.
- Parameters
residue (L{Residue} or string) – a L{Residue} object OR a three letter amino acid code
standard (boolean) – flag to check for the 20 AA (default false)
>>> is_aa('ALA') True
Known three letter codes for modified amino acids are supported,
>>> is_aa('FME') True >>> is_aa('FME', standard=True) False
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class
Bio.PDB.Polypeptide.Polypeptide(iterable=(), /)¶ Bases:
listA polypeptide is simply a list of L{Residue} objects.
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get_ca_list(self)¶ Get list of C-alpha atoms in the polypeptide.
- Returns
the list of C-alpha atoms
- Return type
[L{Atom}, L{Atom}, ..]
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get_phi_psi_list(self)¶ Return the list of phi/psi dihedral angles.
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get_tau_list(self)¶ List of tau torsions angles for all 4 consecutive Calpha atoms.
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get_theta_list(self)¶ List of theta angles for all 3 consecutive Calpha atoms.
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get_sequence(self)¶ Return the AA sequence as a Seq object.
- Returns
polypeptide sequence
- Return type
L{Seq}
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__repr__(self)¶ Return string representation of the polypeptide.
Return <Polypeptide start=START end=END>, where START and END are sequence identifiers of the outer residues.
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