Bio.PDB.internal_coords module¶

Classes to support internal coordinates for protein structures.

Internal coordinates comprise Psi, Phi and Omega dihedral angles along the protein backbone, Chi angles along the sidechains, and all 3-atom angles and bond lengths comprising a protein chain. These routines can compute internal coordinates from atom XYZ coordinates, and compute atom XYZ coordinates from internal coordinates.

Internal coordinates are defined on sequences of atoms which span residues or follow accepted nomenclature along sidechains. To manage these sequences and support Biopython’s disorder mechanisms, AtomKey specifiers are implemented to capture residue, atom and variant identification in a single object. A Hedron object is specified as three sequential AtomKeys, comprising two bond lengths and the bond angle between them. A Dihedron consists of four sequential AtomKeys, linking two Hedra with a dihedral angle between them.

A Protein Internal Coordinate (.pic) file format is defined to capture sufficient detail to reproduce a PDB file from chain starting coordinates (first residue N, Ca, C XYZ coordinates) and remaining internal coordinates. These files are used internally to verify that a given structure can be regenerated from its internal coordinates.

Internal coordinates may also be exported as OpenSCAD data arrays for generating 3D printed protein models. OpenSCAD software is provided as proof-of-concept for generating such models.

The following classes comprise the core functionality for processing internal coordinates and are sufficiently related and coupled to place them together in this module:

IC_Chain: Extends Biopython Chain on .internal_coord attribute.: Manages connected sequence of residues and chain breaks; methods generally apply IC_Residue methods along chain.
IC_Residue: Extends for Biopython Residue on .internal_coord attribute.: Most control and methods of interest are in this class, see API.
Dihedron: four joined atoms forming a dihedral angle.: Dihedral angle, homogeneous atom coordinates in local coordinate space, references to relevant Hedra and IC_Residue. Methods to compute residue dihedral angles, bond angles and bond lengths.
Hedron: three joined atoms forming a plane.: Contains homogeneous atom coordinates in local coordinate space as well as bond lengths and angle between them.
Edron: base class for Hedron and Dihedron classes.: Tuple of AtomKeys comprising child, string ID, mainchain membership boolean and other routines common for both Hedra and Dihedra. Implements rich comparison.
AtomKey: keys (dictionary and string) for referencing atom sequences.: Capture residue and disorder/occupancy information, provides a no-whitespace key for .pic files, and implements rich comparison.

Custom exception classes: HedronMatchError and MissingAtomError

class Bio.PDB.internal_coords.IC_Chain(parent: Chain, verbose: bool = False)¶

Bases: object

Class to extend Biopython Chain with internal coordinate data.

Attributes

chain: biopython Chain object reference: The Chain object this extends
initNCaC: AtomKey indexed dictionary of N, Ca, C atom coordinates.: NCaCKeys start chain segments (first residue or after chain break). These 3 atoms define the coordinate space for a contiguous chain segment, as initially specified by PDB or mmCIF file.
MaxPeptideBond: **Class attribute to detect chain breaks.**: Override for fully contiguous chains with some very long bonds - e.g. for 3D printing (OpenSCAD output) a structure with fully disordered (missing) residues.
ordered_aa_ic_list: list of IC_Residue objects: IC_Residue objects ic algorithms can process (e.g. no waters)
hedra: dict indexed by 3-tuples of AtomKeys: Hedra forming residues in this chain
hedraLen: int length of hedra dict
hedraNdx: dict mapping hedra AtomKeys to numpy array data
dihedra: dict indexed by 4-tuples of AtomKeys: Dihedra forming (overlapping) this residue
dihedraLen: int length of dihedra dict
dihedraNdx: dict mapping dihedra AtomKeys to numpy array data
atomArray: numpy array of homogeneous atom coords for chain
atomArrayIndex: dict mapping AtomKeys to atomArray indexes
numpy arrays for vector processing of chain di/hedra:
hedraIC: length-angle-length entries for each hedron
hAtoms: homogeneous atom coordinates (3x4) of hedra, central atom at origin
hAtomsR: hAtoms in reverse order
hAtoms_needs_update: booleans indicating whether hAtoms represent hedraIC
dihedraIC: dihedral angles for each dihedron
dAtoms: homogeneous atom coordinates (4x4) of dihedra, second atom at origin
dAtoms_needs_update: booleans indicating whether dAtoms represent dihedraIC

Methods

internal_to_atom_coordinates(verbose, start, fin)	Process ic data to Residue/Atom coordinates; calls assemble_residues() followed by coords_to_structure()
assemble_residues(verbose, start, fin)	Generate IC_Residue atom coords from internal coordinates
coords_to_structure()	update Biopython Residue.Atom coords from IC_Residue coords for all Residues with IC_Residue attributes
atom_to_internal_coordinates(verbose)	Calculate dihedrals, angles, bond lengths (internal coordinates) for Atom data
link_residues()	Call link_dihedra() on each IC_Residue (needs rprev, rnext set)
set_residues()	Add .internal_coord attribute for all Residues in parent Chain, populate ordered_aa_ic_list, set IC_Residue rprev, rnext or initNCaC coordinates
write_SCAD()	Write OpenSCAD matrices for internal coordinate data comprising chain

MaxPeptideBond = 1.4¶

__init__(self, parent: ‘Chain’, verbose: bool = False) → None¶

Initialize IC_Chain object, with or without residue/Atom data.

Parameters: parent – Biopython Chain object Chain object this extends

clear_ic(self)¶: Clear residue internal_coord settings for this chain.

set_residues(self, verbose: bool = False) → None¶

Initialize internal_coord data for loaded Residues.

Add IC_Residue as .internal_coord attribute for each Residue in parent Chain; populate ordered_aa_ic_list with IC_Residue references for residues which can be built (amino acids and some hetatms); set rprev and rnext on each sequential IC_Residue, populate initNCaC at start and after chain breaks.

link_residues(self) → None¶

link_dihedra() for each IC_Residue; needs rprev, rnext set.

Called by PICIO:read_PIC() after finished reading chain

assemble_residues(self, verbose: bool = False, start: Union[int, NoneType] = None, fin: Union[int, NoneType] = None) → None¶

Generate IC_Residue atom coords from internal coordinates.

Filter positions between start and fin if set, find appropriate start coordinates for each residue and pass to IC_Residue.assemble()

Parameters: bool (verbose) – default False describe runtime problems
Param: start, fin lists sequence position, insert code for begin, end of subregion to process

coords_to_structure(self) → None¶

Promote all ic atom_coords to Biopython Residue/Atom coords.

IC atom_coords are homogeneous [4], Biopython atom coords are XYZ [3].

init_edra(self) → None¶

Create chain level di/hedra arrays.

If called by read_PIC, self.di/hedra = {} and object tree has IC data. -> build chain arrays from IC data

If called at start of atom_to_internal_coords, self.di/hedra fully populated. -> create empty chain numpy arrays

In both cases, fix di/hedra object attributes to be views on chain-level array data

init_atom_coords(self) → None¶: Set chain level di/hedra initial coord arrays from IC_Residue data.

internal_to_atom_coordinates(self, verbose: bool = False, start: Union[int, NoneType] = None, fin: Union[int, NoneType] = None, promote: Union[bool, NoneType] = True) → None¶

Process, IC data to Residue/Atom coords.

Not yet vectorized.

Parameters

bool (promote) – default False describe runtime problems
bool – default True If True (the default) copy result atom XYZ coordinates to Biopython Atom objects for access by other Biopython methods; otherwise, updated atom coordinates must be accessed through IC_Residue and hedron objects.

Param

start, fin lists sequence position, insert code for begin, end of subregion to process

atom_to_internal_coordinates(self, verbose: bool = False) → None¶

Calculate dihedrals, angles, bond lengths for Atom data.

Parameters: bool (verbose) – default False describe runtime problems

write_SCAD(self, fp: <class 'TextIO'>, backboneOnly: bool) → None¶

Write self to file fp as OpenSCAD data matrices.

Works with write_SCAD() and embedded OpenSCAD routines in SCADIO.py. The OpenSCAD code explicitly creates spheres and cylinders to represent atoms and bonds in a 3D model. Options are available to support rotatable bonds and magnetic hydrogen bonds.

Matrices are written to link, enumerate and describe residues, dihedra, hedra, and chains, mirroring contents of the relevant IC_* data structures.

The OpenSCAD matrix of hedra has additional information as follows:

the atom and bond state (single, double, resonance) are logged so that covalent radii may be used for atom spheres in the 3D models
bonds and atoms are tracked so that each is only created once
bond options for rotation and magnet holders for hydrogen bonds may be specified

Note the application of IC_Chain attribute MaxPeptideBond: missing residues may be linked (joining chain segments with arbitrarily long bonds) by setting this to a large value.

All ALTLOC (disordered) residues and atoms are written to the output model.

class Bio.PDB.internal_coords.IC_Residue(parent: Residue, NO_ALTLOC: bool = False)¶

Bases: object

Class to extend Biopython Residue with internal coordinate data.

Parameters

parent: biopython Residue object this class extends
NO_ALTLOC: bool default False
Disable processing of ALTLOC atoms if True, use only selected atoms.

Attributes

residue: Biopython Residue object reference

The Residue object this extends

hedra: dict indexed by 3-tuples of AtomKeys

Hedra forming this residue

dihedra: dict indexed by 4-tuples of AtomKeys

Dihedra forming (overlapping) this residue

rprev, rnext: lists of IC_Residue objects

References to adjacent (bonded, not missing, possibly disordered) residues in chain

atom_coords: AtomKey indexed dict of numpy [4] arrays

Local copy of atom homogeneous coordinates [4] for work distinct from Bopython Residue/Atom values

alt_ids: list of char

AltLoc IDs from PDB file

bfactors: dict

AtomKey indexed B-factors as read from PDB file

NCaCKey: List of tuples of AtomKeys

List of tuples of N, Ca, C backbone atom AtomKeys; usually only 1 but more if backbone altlocs. Set by link_dihedra()

is20AA: bool

True if residue is one of 20 standard amino acids, based on Residue resname

accept_atoms: tuple

list of PDB atom names to use when generatiing internal coordinates. Default is:

accept_atoms = accept_mainchain + accept_hydrogens

to exclude hydrogens in internal coordinates and generated PDB files, override as:

IC_Residue.accept_atoms = IC_Residue.accept_mainchain

to get only backbone atoms plus amide proton, use:

IC_Residue.accept_atoms = IC_Residue.accept_mainchain + (‘H’,)

to convert D atoms to H, set AtomKey.d2h = True and use:

IC_Residue.accept_atoms = accept_mainchain + accept_hydrogens + accept_deuteriums

There is currently no option to output internal coordinates with D instead of H

accept_resnames: tuple

list of 3-letter residue names for HETATMs to accept when generating internal coordinates from atoms. HETATM sidechain will be ignored, but normal backbone atoms (N, CA, C, O, CB) will be included. Currently only CYG, YCM and UNK; override at your own risk. To generate sidechain, add appropriate entries to ic_data_sidechains in ic_data.py and support in atom_to_internal_coordinates()

gly_Cbeta: bool default False

override class variable to True to generate internal coordinates for glycine CB atoms in atom_to_internal_coordinates().

IC_Residue.gly_Cbeta = True

allBonds: bool default False

whereas a PDB file just specifies atoms, OpenSCAD output for 3D printing needs all bonds specified explicitly - otherwise, e.g. PHE rings will not be closed. This variable is managed by the Write_SCAD() code and enables this.

cic: IC_Chain default None

parent chain IC_Chain object

scale: optional float

used for OpenSCAD output to generate gly_Cbeta bond length

Methods

applyMtx()	multiply all IC_Residue atom_cords by passed matrix
assemble(atomCoordsIn, resetLocation, verbose)	Compute atom coordinates for this residue from internal coordinates
atm241(coord)	Convert 1x3 cartesian coords to 4x1 homogeneous coords
coords_to_residue()	Convert homogeneous atom_coords to Biopython cartesian Atom coords
atom_to_internal_coordinates(verbose)	Create hedra and dihedra for atom coordinates
get_angle()	Return angle for passed key
get_length()	Return bond length for specified pair
link_dihedra()	Link dihedra to this residue, form id3_dh_index
load_PIC(edron)	Process parsed (di-/h-)edron data from PIC file
pick_angle()	Find Hedron or Dihedron for passed key
pick_length()	Find hedra for passed AtomKey pair
rak(atom info)	Residue AtomKey - per residue AtomKey result cache
set_angle()	Set angle for passed key (no position updates)
set_length()	Set bond length in all relevant hedra for specified pair
write_PIC(pdbid, chainId, s)	Generate PIC format strings for this residue

accept_resnames = ('CYG', 'YCM', 'UNK')¶

AllBonds: bool = False¶

__init__(self, parent: ‘Residue’, NO_ALTLOC: bool = False) → None¶

Initialize IC_Residue with parent Biopython Residue.

Parameters

parent – Biopython Residue object The Biopython Residue this object extends
NO_ALTLOC – bool default False Option to disable processing altloc disordered atoms, use selected.

rak(self, atm: Union[str, Bio.PDB.Atom.Atom]) → ’AtomKey’¶: Cache calls to AtomKey for this residue.

build_rak_cache(self) → None¶: Create explicit entries for for atoms so don’t miss altlocs.

accept_mainchain = ('N', 'CA', 'C', 'O', 'CB', 'CG', 'CG1', 'OG1', 'OG', 'SG', 'CG2', 'CD', 'CD1', 'SD', 'OD1', 'ND1', 'CD2', 'ND2', 'CE', 'CE1', 'NE', 'OE1', 'NE1', 'CE2', 'OE2', 'NE2', 'CE3', 'CZ', 'NZ', 'CZ2', 'CZ3', 'OD2', 'OH', 'CH2', 'OXT')¶

accept_hydrogens = ('H', 'H1', 'H2', 'H3', 'HA', 'HA2', 'HA3', 'HB', 'HB1', 'HB2', 'HB3', 'HG2', 'HG3', 'HD2', 'HD3', 'HE2', 'HE3', 'HZ1', 'HZ2', 'HZ3', 'HG11', 'HG12', 'HG13', 'HG21', 'HG22', 'HG23', 'HZ', 'HD1', 'HE1', 'HD11', 'HD12', 'HD13', 'HG', 'HG1', 'HD21', 'HD22', 'HD23', 'NH1', 'NH2', 'HE', 'HH11', 'HH12', 'HH21', 'HH22', 'HE21', 'HE22', 'HE2', 'HH', 'HH2')¶

accept_deuteriums = ('D', 'D1', 'D2', 'D3', 'DA', 'DA2', 'DA3', 'DB', 'DB1', 'DB2', 'DB3', 'DG2', 'DG3', 'DD2', 'DD3', 'DE2', 'DE3', 'DZ1', 'DZ2', 'DZ3', 'DG11', 'DG12', 'DG13', 'DG21', 'DG22', 'DG23', 'DZ', 'DD1', 'DE1', 'DD11', 'DD12', 'DD13', 'DG', 'DG1', 'DD21', 'DD22', 'DD23', 'ND1', 'ND2', 'DE', 'DH11', 'DH12', 'DH21', 'DH22', 'DE21', 'DE22', 'DE2', 'DH', 'DH2')¶

accept_atoms = ('N', 'CA', 'C', 'O', 'CB', 'CG', 'CG1', 'OG1', 'OG', 'SG', 'CG2', 'CD', 'CD1', 'SD', 'OD1', 'ND1', 'CD2', 'ND2', 'CE', 'CE1', 'NE', 'OE1', 'NE1', 'CE2', 'OE2', 'NE2', 'CE3', 'CZ', 'NZ', 'CZ2', 'CZ3', 'OD2', 'OH', 'CH2', 'OXT', 'H', 'H1', 'H2', 'H3', 'HA', 'HA2', 'HA3', 'HB', 'HB1', 'HB2', 'HB3', 'HG2', 'HG3', 'HD2', 'HD3', 'HE2', 'HE3', 'HZ1', 'HZ2', 'HZ3', 'HG11', 'HG12', 'HG13', 'HG21', 'HG22', 'HG23', 'HZ', 'HD1', 'HE1', 'HD11', 'HD12', 'HD13', 'HG', 'HG1', 'HD21', 'HD22', 'HD23', 'NH1', 'NH2', 'HE', 'HH11', 'HH12', 'HH21', 'HH22', 'HE21', 'HE22', 'HE2', 'HH', 'HH2')¶

gly_Cbeta = False¶

static atm241(coord: <built-in function array>) → <built-in function array>¶: Convert 1x3 cartesian coordinates to 4x1 homogeneous coordinates.

__repr__(self) → str¶: Print string is parent Residue ID.

pretty_str(self) → str¶: Nice string for residue ID.

load_PIC(self, edron: Dict[str, str]) → None¶

Process parsed (di-/h-)edron data from PIC file.

Parameters: edron – parse dictionary from Edron.edron_re

link_dihedra(self, verbose: bool = False) → None¶

Housekeeping after loading all residues and dihedra.

Link dihedra to this residue
form id3_dh_index
form ak_set
set NCaCKey to be available AtomKeys

set_flexible(self) → None¶: For OpenSCAD, mark N-CA and CA-C bonds to be flexible joints.

set_hbond(self) → None¶: For OpenSCAD, mark H-N and C-O bonds to be hbonds (magnets).

default_startpos(self) → Dict[ForwardRef(‘AtomKey’), <built-in function array>]¶: Generate default N-Ca-C coordinates to build this residue from.

get_startpos(self) → Dict[ForwardRef(‘AtomKey’), <built-in function array>]¶: Find N-Ca-C coordinates to build this residue from.

clear_transforms(self)¶: Set cst and rcst attributes to none before assemble().

assemble(self, resetLocation: bool = False, verbose: bool = False) → Union[Dict[ForwardRef(‘AtomKey’), <built-in function array>], Dict[Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], <built-in function array>], NoneType]¶

Compute atom coordinates for this residue from internal coordinates.

Join dihedrons starting from N-CA-C and N-CA-CB hedrons, computing protein space coordinates for backbone and sidechain atoms

Sets forward and reverse transforms on each Dihedron to convert from protein coordinates to dihedron space coordinates for first three atoms (see coord_space())

Not vectorized (yet).

Algorithm

form double-ended queue, start with c-ca-n, o-c-ca, n-ca-cb, n-ca-c.

if resetLocation=True, use initial coords from generating dihedron for n-ca-c initial positions (result in dihedron coordinate space)

while queue not empty

get 3-atom hedron key

for each dihedron starting with hedron key (1st hedron of dihedron)

if have coordinates for all 4 atoms already
add 2nd hedron key to back of queue

else if have coordinates for 1st 3 atoms
compute forward and reverse transforms to take 1st 3 atoms to/from dihedron initial coordinate space

use reverse transform to get position of 4th atom in current coordinates from dihedron initial coordinates

add 2nd hedron key to back of queue

else
ordering failed, put hedron key at back of queue and hope next time we have 1st 3 atom positions (should not happen)

loop terminates (queue drains) as hedron keys which do not start any dihedra are removed without action

Parameters: resetLocation – bool default False - Option to ignore start location and orient so N-Ca-C hedron at origin.
Returns: Dict of AtomKey -> homogeneous atom coords for residue in protein space relative to previous residue

atom_to_internal_coordinates(self, verbose: bool = False) → None¶

Create hedra and dihedra for atom coordinates.

Parameters: verbose – bool default False warn about missing N, Ca, C backbone atoms.

build_glyCB(self, gCBd: ‘Dihedron’)¶

Populate values for Gly C-beta, rest of chain complete.

Data averaged from Sep 2019 Dunbrack cullpdb_pc20_res2.2_R1.0 restricted to structures with amide protons.

Ala avg rotation of OCCACB from NCACO query: select avg(g.rslt) as avg_rslt, stddev(g.rslt) as sd_rslt, count(*) from (select f.d1d, f.d2d, (case when f.rslt > 0 then f.rslt-360.0 else f.rslt end) as rslt from (select d1.angle as d1d, d2.angle as d2d, (d2.angle - d1.angle) as rslt from dihedron d1, dihedron d2 where d1.rdh_class=’AOACACAACB’ and d2.rdh_class=’ANACAACAO’ and d1.pdb=d2.pdb and d1.chn=d2.chn and d1.res=d2.res) as f) as g

avg_rslt | sd_rslt | count |

-122.682194862932 | 5.04403040513919 | 14098 |

write_PIC(self, pdbid: str = '0PDB', chainid: str = 'A', s: str = '') → str¶

Write PIC format lines for this residue.

Parameters

pdbid (str) – PDB idcode string; default 0PDB
chainid (str) – PDB Chain ID character; default A
s (str) – result string to add to

coords_to_residue(self, rnext: bool = False) → None¶

Convert self.atom_coords to biopython Residue Atom coords.

Copy homogeneous IC_Residue atom_coords to self.residue cartesian Biopython Atom coords.

Parameters: rnext – bool default False next IC_Residue has no atom coords due to missing atoms, so try to populate with any available coords calculated for this residue di/hedra extending into next

relative_atom_re = re.compile('^(-?[10])([A-Z]+)$')¶

pick_angle(self, angle_key: Union[Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], str]) → Union[ForwardRef(‘Hedron’), ForwardRef(‘Dihedron’), NoneType]¶

Get Hedron or Dihedron for angle_key.

Parameters

angle_key –

tuple of 3 or 4 AtomKeys
string of atom names (‘CA’) separated by :’s
string of [-1, 0, 1]<atom name> separated by ‘:’s. -1 is previous residue, 0 is this residue, 1 is next residue
psi, phi, omg, omega, chi1, chi2, chi3, chi4, chi5
tau (N-CA-C angle) see Richardson1981
except for tuples of AtomKeys, no option to access alternate disordered atoms

Observe that a residue’s phi and omega dihedrals, as well as the hedra comprising them (including the N:Ca:C tau hedron), are stored in the n-1 di/hedra sets; this is handled here, but may be an issue if accessing directly.

The following are equivalent (except for sidechains with non-carbon atoms for chi2):

ric = r.internal_coord
print(
    r,
    ric.get_angle("psi"),
    ric.get_angle("phi"),
    ric.get_angle("omg"),
    ric.get_angle("tau"),
    ric.get_angle("chi2"),
)
print(
    r,
    ric.get_angle("N:CA:C:1N"),
    ric.get_angle("-1C:N:CA:C"),
    ric.get_angle("-1CA:-1C:N:CA"),
    ric.get_angle("N:CA:C"),
    ric.get_angle("CA:CB:CG:CD"),
)

See ic_data.py for detail of atoms in the enumerated sidechain angles and the backbone angles which do not span the peptide bond. Using ‘s’ for current residue (‘self’) and ‘n’ for next residue, the spanning angles are:

(sN, sCA, sC, nN)   # psi
(sCA, sC, nN, nCA)  # omega i+1
(sC, nN, nCA, nC)   # phi i+1
(sCA, sC, nN)
(sC, nN, nCA)
(nN, nCA, nC)       # tau i+1

Returns: Matching Hedron, Dihedron, or None.

get_angle(self, angle_key: Union[Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], str]) → Union[float, NoneType]¶

Get dihedron or hedron angle for specified key.

See pick_angle() for key specifications.

set_angle(self, angle_key: Union[Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], str], v: float)¶

Set dihedron or hedron angle for specified key.

See pick_angle() for key specifications.

pick_length(self, ak_spec: Union[str, Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)]]) → Tuple[Union[List[ForwardRef(‘Hedron’)], NoneType], Union[Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], NoneType]]¶

Get list of hedra containing specified atom pair.

Parameters

ak_spec –

tuple of two AtomKeys
string: two atom names separated by ‘:’, e.g. ‘N:CA’ with optional position specifier relative to self, e.g. ‘-1C:N’ for preceding peptide bond.

The following are equivalent:

ric = r.internal_coord
print(
    r,
    ric.get_length("0C:1N"),
)
print(
    r,
    None
    if not ric.rnext
    else ric.get_length((ric.rak("C"), ric.rnext[0].rak("N"))),
)

Returns: list of hedra containing specified atom pair, tuple of atom keys

get_length(self, ak_spec: Union[str, Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)]]) → Union[float, NoneType]¶

Get bond length for specified atom pair.

See pick_length() for ak_spec.

set_length(self, ak_spec: Union[str, Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)]], val: float) → None¶

Set bond length for specified atom pair.

See pick_length() for ak_spec.

applyMtx(self, mtx: <built-in function array>) → None¶: Apply matrix to atom_coords for this IC_Residue.

__annotations__ = {'AllBonds': <class 'bool'>, 'ak_set': 'Set[AtomKey]', 'akc': 'Dict[Union[str, Atom], AtomKey]', 'alt_ids': 'Union[List[str], None]', 'atom_coords': "Dict['AtomKey', numpy.array]", 'bfactors': 'Dict[str, float]', 'cic': 'IC_Chain', 'dihedra': 'Dict[DKT, Dihedron]', 'hedra': 'Dict[HKT, Hedron]', 'id3_dh_index': 'Dict[HKT, List[Dihedron]]', 'rnext': 'List[IC_Residue]', 'rprev': 'List[IC_Residue]'}¶

class Bio.PDB.internal_coords.Edron(*args: Union[List[Bio.PDB.internal_coords.AtomKey], Tuple[Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey], Tuple[Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey]], **kwargs: str)¶

Bases: object

Base class for Hedron and Dihedron classes.

Supports rich comparison based on lists of AtomKeys.

Attributes

aks: tuple: 3 (hedron) or 4 (dihedron) AtomKeys defining this di/hedron
id: str: ‘:’-joined string of AtomKeys for this di/hedron
needs_update: bool: indicates di/hedron local atom_coords do NOT reflect current di/hedron angle and length values in hedron local coordinate space
dh_class: str: sequence of atoms (no position or residue) comprising di/hedron for statistics
rdh_class: str: sequence of residue, atoms comprising di/hedron for statistics
edron_re: compiled regex (Class Attribute): A compiled regular expression matching string IDs for Hedron and Dihedron objects
cic: IC_Chain reference: Chain internal coords object containing this hedron

Methods

gen_key([AtomKey, …] or AtomKey, …) (Static Method)	generate a ‘:’-joined string of AtomKey Ids
gen_acs(atom_coords)	generate tuple of atom coords for keys in self.aks
is_backbone()	Return True if all aks atoms are N, Ca, C or O

edron_re = re.compile('^(?P<pdbid>\\w+)?\\s(?P<chn>[\\w|\\s])?\\s(?P<a1>[\\w\\-\\.]+):(?P<a2>[\\w\\-\\.]+):(?P<a3>[\\w\\-\\.]+)(:(?P<a4>[\\w\\-\\.]+))?\\s+(((?P<len12>\\S+)\\s+(?P<angle>\\S+)\\s+(?P<len23>\\S+)\\s*$)|((?P<)¶

static gen_key(lst: Union[List[str], List[ForwardRef(‘AtomKey’)]]) → str¶

Generate string of ‘:’-joined AtomKey strings from input.

Parameters: lst – list of AtomKey objects or id strings

__init__(self, *args: Union[List[ForwardRef(‘AtomKey’)], Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)]], **kwargs: str) → None¶

Initialize Edron with sequence of AtomKeys.

Acceptable input:

[ AtomKey, … ] : list of AtomKeys AtomKey, … : sequence of AtomKeys as args {‘a1’: str, ‘a2’: str, … } : dict of AtomKeys as ‘a1’, ‘a2’ …

gen_acs(self, atom_coords: Dict[ForwardRef('AtomKey'), <built-in function array>]) → Tuple[<built-in function array>, …]¶

Generate tuple of atom coord arrays for keys in self.aks.

Parameters: atom_coords – AtomKey dict of atom coords for residue
Raises: MissingAtomError any atoms in self.aks missing coordinates

is_backbone(self) → bool¶: Report True for contains only N, C, CA, O, H atoms.

__repr__(self) → str¶: Tuple of AtomKeys is default repr string.

__hash__(self) → int¶: Hash calculated at init from aks tuple.

__eq__(self, other: object) → bool¶: Test for equality.

__ne__(self, other: object) → bool¶: Test for inequality.

__gt__(self, other: object) → bool¶: Test greater than.

__ge__(self, other: object) → bool¶: Test greater or equal.

__lt__(self, other: object) → bool¶: Test less than.

__le__(self, other: object) → bool¶: Test less or equal.

class Bio.PDB.internal_coords.Hedron(*args: Union[List[Bio.PDB.internal_coords.AtomKey], Tuple[Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey]], **kwargs: str)¶

Bases: Bio.PDB.internal_coords.Edron

Class to represent three joined atoms forming a plane.

Contains atom coordinates in local coordinate space, central atom at origin. Stored in two orientations, with the 3rd (forward) or first (reversed) atom on the +Z axis.

Attributes

lal: numpy array of len12, angle, len23: len12 = distance between 1st and 2nd atom angle = angle (degrees) formed by 3 atoms len23 = distance between 2nd and 3rd atoms
atoms: 3x4 numpy arrray (view on chain array): 3 homogeneous atoms comprising hedron, 1st on XZ, 2nd at origin, 3rd on +Z
atomsR: 3x4 numpy array (view on chain array): atoms reversed, 1st on +Z, 2nd at origin, 3rd on XZ plane

Methods

get_length()	get bond length for specified atom pair
set_length()	set bond length for specified atom pair
angle(), len12(), len23()	gettters and setters for relevant attributes (angle in degrees)

__init__(self, *args: Union[List[ForwardRef(‘AtomKey’)], Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)]], **kwargs: str) → None¶

Initialize Hedron with sequence of AtomKeys, kwargs.

Acceptable input:: As for Edron, plus optional ‘len12’, ‘angle’, ‘len23’ keyworded values.

__repr__(self) → str¶: Print string for Hedron object.

property angle: float¶: Get this hedron angle.

property len12¶: Get first length for Hedron.

property len23: float¶: Get second length for Hedron.

get_length(self, ak_tpl: Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)]) → Union[float, NoneType]¶

Get bond length for specified atom pair.

Parameters: ak_tpl – tuple of AtomKeys pair of atoms in this Hedron

set_length(self, ak_tpl: Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)], newLength: float)¶

Set bond length for specified atom pair; sets needs_update.

Parameters: ak_tpl – tuple of AtomKeys pair of atoms in this Hedron

cic: Bio.PDB.internal_coords.IC_Chain¶

class Bio.PDB.internal_coords.Dihedron(*args: Union[List[Bio.PDB.internal_coords.AtomKey], Tuple[Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey, Bio.PDB.internal_coords.AtomKey]], **kwargs: str)¶

Bases: Bio.PDB.internal_coords.Edron

Class to represent four joined atoms forming a dihedral angle.

Attributes

angle: float: Measurement or specification of dihedral angle in degrees
hedron1, hedron2: Hedron object references: The two hedra which form the dihedral angle
h1key, h2key: tuples of AtomKeys: Hash keys for hedron1 and hedron2
id3,id32: tuples of AtomKeys: First 3 and second 3 atoms comprising dihedron; hxkey orders may differ
initial_coords: tuple[4] of numpy arrays [4]: Local atom coords for 4 atoms, [0] on XZ plane, [1] at origin, [2] on +Z, [3] rotated by dihedral
a4_pre_rotation: numpy array [4]: 4th atom of dihedral aligned to XZ plane (angle not applied)
ic_residue: IC_Residue object reference: IC_Residue object containing this dihedral
reverse: bool: Indicates order of atoms in dihedron is reversed from order of atoms in hedra (configured by set_hedra())
cst, rcst: numpy array [4][4]: transforms to and from coordinate space defined by first hedron. set by IC_Residue.assemble(). defined by id3 order NOT h1key order (atoms may be reversed between these two)

Methods

set_hedra()	work out hedra keys and orientation for this dihedron
angle()	getter/setter for dihdral angle in degrees

__init__(self, *args: Union[List[ForwardRef(‘AtomKey’)], Tuple[ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’), ForwardRef(‘AtomKey’)]], **kwargs: str) → None¶

Initialize Dihedron with sequence of AtomKeys and optional dihedral angle.

Acceptable input:: As for Edron, plus optional ‘dihedral’ keyworded angle value.

__repr__(self) → str¶: Print string for Dihedron object.

set_hedra(self) → Tuple[bool, Bio.PDB.internal_coords.Hedron, Bio.PDB.internal_coords.Hedron]¶: Work out hedra keys and set rev flag.

property angle: float¶: Get dihedral angle.

cic: Bio.PDB.internal_coords.IC_Chain¶

class Bio.PDB.internal_coords.AtomKey(*args: Union[Bio.PDB.internal_coords.IC_Residue, Bio.PDB.Atom.Atom, List, Dict, str], **kwargs: str)¶

Bases: object

Class for dict keys to reference atom coordinates.

AtomKeys capture residue and disorder information together, and provide a no-whitespace string key for .pic files.

Supports rich comparison and multiple ways to instantiate.

AtomKeys contain:: residue position, insertion code, 1 or 3 char residue name, atom name, altloc, and occupancy

Attributes

akl: tuple: All six fields of AtomKey
fieldNames: tuple (Class Attribute): Mapping of key index positions to names
fields: namedtuple (Class Attribute): Mapping of field names to index positions
id: str: ‘_’-joined AtomKey fields, excluding ‘None’ fields
atom_re: compiled regex (Class Attribute): A compiled regular expression matching the string form of the key
endnum_re: compiled regex (Class Attribute): A compiled regular expresion capturing digits at end of a string
d2h: bool (Class Attribute): Convert D atoms to H on input; must also modify IC_Residue.accept_atoms
missing: bool default False: AtomKey __init__’d from string is probably missing, set this flag to note the issue (not set here)

Methods

altloc_match(other)

Returns True if this AtomKey matches other AtomKey excluding altloc and occupancy fields

atom_re = re.compile('^(?P<respos>-?\\d+)(?P<icode>[A-Za-z])?_(?P<resname>[a-zA-Z]+)_(?P<atm>[A-Za-z0-9]+)(?:_(?P<altloc>\\w))?(?:_(?P<occ>-?\\d\\.\\d?\\d?))?$')¶

endnum_re = re.compile('\\D+(\\d+)$')¶

fieldNames = ('respos', 'icode', 'resname', 'atm', 'altloc', 'occ')¶

class fieldsDef(respos, icode, resname, atm, altloc, occ)¶

Bases: tuple

__getnewargs__(self)¶: Return self as a plain tuple. Used by copy and pickle.

static __new__(_cls, respos, icode, resname, atm, altloc, occ)¶: Create new instance of fieldsDef(respos, icode, resname, atm, altloc, occ)

__repr__(self)¶: Return a nicely formatted representation string

__slots__ = ()¶

property altloc¶: Alias for field number 4

property atm¶: Alias for field number 3

property icode¶: Alias for field number 1

property occ¶: Alias for field number 5

property resname¶: Alias for field number 2

property respos¶: Alias for field number 0

fields = fieldsDef(respos=0, icode=1, resname=2, atm=3, altloc=4, occ=5)¶

d2h = False¶

__init__(self, *args: Union[Bio.PDB.internal_coords.IC_Residue, Bio.PDB.Atom.Atom, List, Dict, str], **kwargs: str) → None¶

Initialize AtomKey with residue and atom data.

Examples of acceptable input:: (<IC_Residue>, ‘CA’, …) : IC_Residue with atom info (<IC_Residue>, <Atom>) : IC_Residue with Biopython Atom ([52, None, ‘G’, ‘CA’, …]) : list of ordered data fields (52, None, ‘G’, ‘CA’, …) : multiple ordered arguments ({respos: 52, icode: None, atm: ‘CA’, …}) : dict with fieldNames (respos: 52, icode: None, atm: ‘CA’, …) : kwargs with fieldNames 52_G_CA, 52B_G_CA, 52_G_CA_0.33, 52_G_CA_B_0.33 : id strings

__repr__(self) → str¶: Repr string from id.

__hash__(self) → int¶: Hash calculated at init from akl tuple.

altloc_match(self, other: ‘AtomKey’) → bool¶: Test AtomKey match other discounting occupancy and altloc.

__ne__(self, other: object) → bool¶: Test for inequality.

__eq__(self, other: object) → bool¶: Test for equality.

__gt__(self, other: object) → bool¶: Test greater than.

__ge__(self, other: object) → bool¶: Test greater or equal.

__lt__(self, other: object) → bool¶: Test less than.

__le__(self, other: object) → bool¶: Test less or equal.

Bio.PDB.internal_coords.set_accuracy_95(num: float) → float¶

Reduce floating point accuracy to 9.5 (xxxx.xxxxx).

Used by Hedron and Dihedron classes writing PIC and SCAD files. :param float num: input number :returns: float with specified accuracy

exception Bio.PDB.internal_coords.HedronMatchError¶

Bases: Exception

Cannot find hedron in residue for given key.

exception Bio.PDB.internal_coords.MissingAtomError¶

Bases: Exception

Missing atom coordinates for hedron or dihedron.