Source code for MDAnalysis.analysis.dihedrals

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r"""Dihedral angles analysis --- :mod:`MDAnalysis.analysis.dihedrals`
=================================================================

:Author: Henry Mull
:Year: 2018
:Copyright: GNU Public License v2

.. versionadded:: 0.19.0

This module contains classes for calculating dihedral angles for a given set of
atoms or residues. This can be done for selected frames or whole trajectories.

A list of time steps that contain angles of interest is generated and can be
easily plotted if desired. For the :class:`~MDAnalysis.analysis.dihedrals.Ramachandran`
and :class:`~MDAnalysis.analysis.dihedrals.Janin` classes, basic plots can be
generated using the method :meth:`Ramachandran.plot` or :meth:`Janin.plot`.
These plots are best used as references, but they also allow for user customization.


See Also
--------
:func:`MDAnalysis.lib.distances.calc_dihedrals()`
   function to calculate dihedral angles from atom positions


Example applications
--------------------

General dihedral analysis
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The :class:`~MDAnalysis.analysis.dihedrals.Dihedral` class is useful for calculating
angles for many dihedrals of interest. For example, we can find the phi angles
for residues 5-10 of adenylate kinase (AdK). The trajectory is included within
the test data files::

   import MDAnalysis as mda
   from MDAnalysisTests.datafiles import GRO, XTC
   u = mda.Universe(GRO, XTC)

   # selection of atomgroups
   ags = [res.phi_selection() for res in u.residues[4:9]]

   from MDAnalysis.analysis.dihedrals import Dihedral
   R = Dihedral(ags).run()

The angles can then be accessed with :attr:`Dihedral.results.angles`.

Ramachandran analysis
~~~~~~~~~~~~~~~~~~~~~

The :class:`~MDAnalysis.analysis.dihedrals.Ramachandran` class allows for the
quick calculation of classical Ramachandran plots :cite:p:`Ramachandran1963` in
the backbone :math:`phi` and :math:`psi` angles. Unlike the
:class:`~MDanalysis.analysis.dihedrals.Dihedral` class which takes a list of
`atomgroups`, this class only needs a list of residues or atoms from those
residues. The previous example can repeated with::

   u = mda.Universe(GRO, XTC)
   r = u.select_atoms("resid 5-10")

   R = Ramachandran(r).run()

Then it can be plotted using the built-in plotting method :meth:`Ramachandran.plot()`::

   import matplotlib.pyplot as plt
   fig, ax = plt.subplots(figsize=plt.figaspect(1))
   R.plot(ax=ax, color='k', marker='o', ref=True)
   fig.tight_layout()

as shown in the example :ref:`Ramachandran plot figure <figure-ramachandran>`.

.. _figure-ramachandran:

.. figure:: /images/rama_demo_plot.png
   :scale: 50 %
   :alt: Ramachandran plot

   Ramachandran plot for residues 5 to 10 of AdK, sampled from the AdK test
   trajectory (XTC). The contours in the background are the "allowed region"
   and the "marginally allowed" regions.

To plot the data yourself, the angles can be accessed using
:attr:`Ramachandran.results.angles`.

.. Note::

   The Ramachandran analysis is prone to errors if the topology contains
   duplicate or missing atoms (e.g. atoms with `altloc` or incomplete
   residues). If the topology has as an `altloc` attribute, you must specify
   only one `altloc` for the atoms with more than one (``"protein and not
   altloc B"``).


Janin analysis
~~~~~~~~~~~~~~

Janin plots :cite:p:`Janin1978` for side chain conformations (:math:`\chi_1`
and :math:`chi_2` angles) can be created with the
:class:`~MDAnalysis.analysis.dihedrals.Janin` class. It works in the same way,
only needing a list of residues; see the :ref:`Janin plot figure
<figure-janin>` as an example.

The data for the angles can be accessed in the attribute
:attr:`Janin.results.angles`.

.. _figure-janin:

.. figure:: /images/janin_demo_plot.png
   :scale: 50 %
   :alt: Janin plot

   Janin plot for all residues of AdK, sampled from the AdK test trajectory
   (XTC). The contours in the background are the "allowed region" and the
   "marginally allowed" regions for all possible residues.

.. Note::

   The Janin analysis is prone to errors if the topology contains duplicate or
   missing atoms (e.g. atoms with `altloc` or incomplete residues). If the
   topology has as an `altloc` attribute, you must specify only one `altloc`
   for the atoms with more than one (``"protein and not altloc B"``).

   Furthermore, many residues do not have a :math:`\chi_2` dihedral and if the
   selections of residues is not carefully filtered to only include those
   residues with *both* sidechain dihedrals then a :exc:`ValueError` with the
   message *Too many or too few atoms selected* is raised.


Reference plots
~~~~~~~~~~~~~~~

Reference plots can be added to the axes for both the Ramachandran and Janin
classes using the kwarg ``ref=True`` for the :meth:`Ramachandran.plot`
and :meth:`Janin.plot` methods. The Ramachandran reference data
(:data:`~MDAnalysis.analysis.data.filenames.Rama_ref`) and Janin reference data
(:data:`~MDAnalysis.analysis.data.filenames.Janin_ref`) were made using data
obtained from a large selection of 500 PDB files, and were analyzed using these
classes :cite:p:`Mull2018`. The allowed and marginally allowed regions of the
Ramachandran reference plot have cutoffs set to include 90% and 99% of the data
points, and the Janin reference plot has cutoffs for 90% and 98% of the data
points. The list of PDB files used for the reference plots was taken from
:cite:p:`Lovell2003` and information about general Janin regions was taken from
:cite:p:`Janin1978`.



Analysis Classes
----------------

.. autoclass:: Dihedral
   :members:
   :inherited-members:

   .. attribute:: results.angles

       Contains the time steps of the angles for each atomgroup in the list as
       an ``n_frames×len(atomgroups)`` :class:`numpy.ndarray` with content
       ``[[angle 1, angle 2, ...], [time step 2], ...]``.

       .. versionadded:: 2.0.0

   .. attribute:: angles

       Alias to the :attr:`results.angles` attribute.

       .. deprecated:: 2.0.0
          Will be removed in MDAnalysis 3.0.0. Please use
          :attr:`results.angles` instead.


.. autoclass:: Ramachandran
   :members:
   :inherited-members:

   .. attribute:: results.angles

       Contains the time steps of the :math:`\phi` and :math:`\psi` angles for
       each residue as an ``n_frames×n_residues×2`` :class:`numpy.ndarray` with
       content ``[[[phi, psi], [residue 2], ...], [time step 2], ...]``.

       .. versionadded:: 2.0.0

   .. attribute:: angles

       Alias to the :attr:`results.angles` attribute.

       .. deprecated:: 2.0.0
          Will be removed in MDAnalysis 3.0.0. Please use
          :attr:`results.angles` instead.


.. autoclass:: Janin
   :members:
   :inherited-members:

   .. attribute:: results.angles

       Contains the time steps of the :math:`\chi_1` and :math:`\chi_2` angles
       for each residue as an ``n_frames×n_residues×2`` :class:`numpy.ndarray`
       with content ``[[[chi1, chi2], [residue 2], ...], [time step 2], ...]``.

       .. versionadded:: 2.0.0

   .. attribute:: angles

       Alias to the :attr:`results.angles` attribute.

       .. deprecated:: 2.0.0
          Will be removed in MDAnalysis 3.0.0. Please use
          :attr:`results.angles` instead.


References
----------

.. bibliography::
    :filter: False
    :style: MDA

    Ramachandran1963
    Janin1978
    Lovell2003
    Mull2018

"""
import numpy as np
import matplotlib.pyplot as plt

import warnings

import MDAnalysis as mda
from MDAnalysis.analysis.base import AnalysisBase
from MDAnalysis.lib.distances import calc_dihedrals
from MDAnalysis.analysis.data.filenames import Rama_ref, Janin_ref


[docs]class Dihedral(AnalysisBase): """Calculate dihedral angles for specified atomgroups. Dihedral angles will be calculated for each atomgroup that is given for each step in the trajectory. Each :class:`~MDAnalysis.core.groups.AtomGroup` must contain 4 atoms. Note ---- This class takes a list as an input and is most useful for a large selection of atomgroups. If there is only one atomgroup of interest, then it must be given as a list of one atomgroup. .. versionchanged:: 2.0.0 :attr:`angles` results are now stored in a :class:`MDAnalysis.analysis.base.Results` instance. """ def __init__(self, atomgroups, **kwargs): """Parameters ---------- atomgroups : list[AtomGroup] a list of :class:`~MDAnalysis.core.groups.AtomGroup` for which the dihedral angles are calculated Raises ------ ValueError If any atomgroups do not contain 4 atoms """ super(Dihedral, self).__init__( atomgroups[0].universe.trajectory, **kwargs) self.atomgroups = atomgroups if any([len(ag) != 4 for ag in atomgroups]): raise ValueError("All AtomGroups must contain 4 atoms") self.ag1 = mda.AtomGroup([ag[0] for ag in atomgroups]) self.ag2 = mda.AtomGroup([ag[1] for ag in atomgroups]) self.ag3 = mda.AtomGroup([ag[2] for ag in atomgroups]) self.ag4 = mda.AtomGroup([ag[3] for ag in atomgroups]) def _prepare(self): self.results.angles = [] def _single_frame(self): angle = calc_dihedrals(self.ag1.positions, self.ag2.positions, self.ag3.positions, self.ag4.positions, box=self.ag1.dimensions) self.results.angles.append(angle) def _conclude(self): self.results.angles = np.rad2deg(np.array(self.results.angles)) @property def angles(self): wmsg = ("The `angle` attribute was deprecated in MDAnalysis 2.0.0 " "and will be removed in MDAnalysis 3.0.0. Please use " "`results.angles` instead") warnings.warn(wmsg, DeprecationWarning) return self.results.angles
[docs]class Ramachandran(AnalysisBase): r"""Calculate :math:`\phi` and :math:`\psi` dihedral angles of selected residues. :math:`\phi` and :math:`\psi` angles will be calculated for each residue corresponding to `atomgroup` for each time step in the trajectory. A :class:`~MDAnalysis.ResidueGroup` is generated from `atomgroup` which is compared to the protein to determine if it is a legitimate selection. Parameters ---------- atomgroup : AtomGroup or ResidueGroup atoms for residues for which :math:`\phi` and :math:`\psi` are calculated c_name : str (optional) name for the backbone C atom n_name : str (optional) name for the backbone N atom ca_name : str (optional) name for the alpha-carbon atom check_protein : bool (optional) whether to raise an error if the provided atomgroup is not a subset of protein atoms Example ------- For standard proteins, the default arguments will suffice to run a Ramachandran analysis:: r = Ramachandran(u.select_atoms('protein')).run() For proteins with non-standard residues, or for calculating dihedral angles for other linear polymers, you can switch off the protein checking and provide your own atom names in place of the typical peptide backbone atoms:: r = Ramachandran(u.atoms, c_name='CX', n_name='NT', ca_name='S', check_protein=False).run() The above analysis will calculate angles from a "phi" selection of CX'-NT-S-CX and "psi" selections of NT-S-CX-NT'. Raises ------ ValueError If the selection of residues is not contained within the protein and ``check_protein`` is ``True`` Note ---- If ``check_protein`` is ``True`` and the residue selection is beyond the scope of the protein and, then an error will be raised. If the residue selection includes the first or last residue, then a warning will be raised and they will be removed from the list of residues, but the analysis will still run. If a :math:`\phi` or :math:`\psi` selection cannot be made, that residue will be removed from the analysis. .. versionchanged:: 1.0.0 added c_name, n_name, ca_name, and check_protein keyword arguments .. versionchanged:: 2.0.0 :attr:`angles` results are now stored in a :class:`MDAnalysis.analysis.base.Results` instance. """ def __init__(self, atomgroup, c_name='C', n_name='N', ca_name='CA', check_protein=True, **kwargs): super(Ramachandran, self).__init__( atomgroup.universe.trajectory, **kwargs) self.atomgroup = atomgroup residues = self.atomgroup.residues if check_protein: protein = self.atomgroup.universe.select_atoms("protein").residues if not residues.issubset(protein): raise ValueError("Found atoms outside of protein. Only atoms " "inside of a 'protein' selection can be used to " "calculate dihedrals.") elif not residues.isdisjoint(protein[[0, -1]]): warnings.warn("Cannot determine phi and psi angles for the first " "or last residues") residues = residues.difference(protein[[0, -1]]) prev = residues._get_prev_residues_by_resid() nxt = residues._get_next_residues_by_resid() keep = np.array([r is not None for r in prev]) keep = keep & np.array([r is not None for r in nxt]) if not np.all(keep): warnings.warn("Some residues in selection do not have " "phi or psi selections") prev = sum(prev[keep]) nxt = sum(nxt[keep]) residues = residues[keep] # find n, c, ca keep_prev = [sum(r.atoms.names==c_name)==1 for r in prev] rnames = [n_name, c_name, ca_name] keep_res = [all(sum(r.atoms.names == n) == 1 for n in rnames) for r in residues] keep_next = [sum(r.atoms.names == n_name) == 1 for r in nxt] # alright we'll keep these keep = np.array(keep_prev) & np.array(keep_res) & np.array(keep_next) prev = prev[keep] res = residues[keep] nxt = nxt[keep] rnames = res.atoms.names self.ag1 = prev.atoms[prev.atoms.names == c_name] self.ag2 = res.atoms[rnames == n_name] self.ag3 = res.atoms[rnames == ca_name] self.ag4 = res.atoms[rnames == c_name] self.ag5 = nxt.atoms[nxt.atoms.names == n_name] def _prepare(self): self.results.angles = [] def _single_frame(self): phi_angles = calc_dihedrals(self.ag1.positions, self.ag2.positions, self.ag3.positions, self.ag4.positions, box=self.ag1.dimensions) psi_angles = calc_dihedrals(self.ag2.positions, self.ag3.positions, self.ag4.positions, self.ag5.positions, box=self.ag1.dimensions) phi_psi = [(phi, psi) for phi, psi in zip(phi_angles, psi_angles)] self.results.angles.append(phi_psi) def _conclude(self): self.results.angles = np.rad2deg(np.array(self.results.angles))
[docs] def plot(self, ax=None, ref=False, **kwargs): """Plots data into standard Ramachandran plot. Each time step in :attr:`Ramachandran.results.angles` is plotted onto the same graph. Parameters ---------- ax : :class:`matplotlib.axes.Axes` If no `ax` is supplied or set to ``None`` then the plot will be added to the current active axes. ref : bool, optional Adds a general Ramachandran plot which shows allowed and marginally allowed regions kwargs : optional All other kwargs are passed to :func:`matplotlib.pyplot.scatter`. Returns ------- ax : :class:`matplotlib.axes.Axes` Axes with the plot, either `ax` or the current axes. """ if ax is None: ax = plt.gca() ax.axis([-180, 180, -180, 180]) ax.axhline(0, color='k', lw=1) ax.axvline(0, color='k', lw=1) ax.set(xticks=range(-180, 181, 60), yticks=range(-180, 181, 60), xlabel=r"$\phi$", ylabel=r"$\psi$") degree_formatter = plt.matplotlib.ticker.StrMethodFormatter( r"{x:g}$\degree$") ax.xaxis.set_major_formatter(degree_formatter) ax.yaxis.set_major_formatter(degree_formatter) if ref: X, Y = np.meshgrid(np.arange(-180, 180, 4), np.arange(-180, 180, 4)) levels = [1, 17, 15000] colors = ['#A1D4FF', '#35A1FF'] ax.contourf(X, Y, np.load(Rama_ref), levels=levels, colors=colors) a = self.results.angles.reshape( np.prod(self.results.angles.shape[:2]), 2) ax.scatter(a[:, 0], a[:, 1], **kwargs) return ax
@property def angles(self): wmsg = ("The `angle` attribute was deprecated in MDAnalysis 2.0.0 " "and will be removed in MDAnalysis 3.0.0. Please use " "`results.angles` instead") warnings.warn(wmsg, DeprecationWarning) return self.results.angles
[docs]class Janin(Ramachandran): r"""Calculate :math:`\chi_1` and :math:`\chi_2` dihedral angles of selected residues. :math:`\chi_1` and :math:`\chi_2` angles will be calculated for each residue corresponding to `atomgroup` for each time step in the trajectory. A :class:`~MDAnalysis.ResidueGroup` is generated from `atomgroup` which is compared to the protein to determine if it is a legitimate selection. Note ---- If the residue selection is beyond the scope of the protein, then an error will be raised. If the residue selection includes the residues ALA, CYS*, GLY, PRO, SER, THR, or VAL (the default of the `select_remove` keyword argument) then a warning will be raised and they will be removed from the list of residues, but the analysis will still run. Some topologies have altloc attributes which can add duplicate atoms to the selection and must be removed. """ def __init__(self, atomgroup, select_remove="resname ALA CYS* GLY PRO SER THR VAL", select_protein="protein", **kwargs): r"""Parameters ---------- atomgroup : AtomGroup or ResidueGroup atoms for residues for which :math:`\chi_1` and :math:`\chi_2` are calculated select_remove : str selection string to remove residues that do not have :math:`chi_2` angles select_protein : str selection string to subselect protein-only residues from `atomgroup` to check that only amino acids are selected; if you have non-standard amino acids then adjust this selection to include them Raises ------ ValueError if the final selection of residues is not contained within the protein (as determined by ``atomgroup.select_atoms(select_protein)``) ValueError if not enough or too many atoms are found for a residue in the selection, usually due to missing atoms or alternative locations, or due to non-standard residues .. versionchanged:: 2.0.0 `select_remove` and `select_protein` keywords were added. :attr:`angles` results are now stored in a :class:`MDAnalysis.analysis.base.Results` instance. """ super(Ramachandran, self).__init__( atomgroup.universe.trajectory, **kwargs) self.atomgroup = atomgroup residues = atomgroup.residues protein = atomgroup.select_atoms(select_protein).residues remove = residues.atoms.select_atoms(select_remove).residues if not residues.issubset(protein): raise ValueError("Found atoms outside of protein. Only atoms " "inside of a protein " f"(select_protein='{select_protein}') can be " "used to calculate dihedrals.") elif len(remove) != 0: warnings.warn(f"All residues selected with '{select_remove}' " "have been removed from the selection.") residues = residues.difference(remove) self.ag1 = residues.atoms.select_atoms("name N") self.ag2 = residues.atoms.select_atoms("name CA") self.ag3 = residues.atoms.select_atoms("name CB") self.ag4 = residues.atoms.select_atoms("name CG CG1") self.ag5 = residues.atoms.select_atoms("name CD CD1 OD1 ND1 SD") # if there is an altloc attribute, too many atoms will be selected which # must be removed before using the class, or the file is missing atoms # for some residues which must also be removed if any(len(self.ag1) != len(ag) for ag in [self.ag2, self.ag3, self.ag4, self.ag5]): raise ValueError("Too many or too few atoms selected. Check for " "missing or duplicate atoms in topology.") def _conclude(self): self.results.angles = (np.rad2deg(np.array( self.results.angles)) + 360) % 360
[docs] def plot(self, ax=None, ref=False, **kwargs): """Plots data into standard Janin plot. Each time step in :attr:`Janin.results.angles` is plotted onto the same graph. Parameters ---------- ax : :class:`matplotlib.axes.Axes` If no `ax` is supplied or set to ``None`` then the plot will be added to the current active axes. ref : bool, optional Adds a general Janin plot which shows allowed and marginally allowed regions kwargs : optional All other kwargs are passed to :func:`matplotlib.pyplot.scatter`. Returns ------- ax : :class:`matplotlib.axes.Axes` Axes with the plot, either `ax` or the current axes. """ if ax is None: ax = plt.gca() ax.axis([0, 360, 0, 360]) ax.axhline(180, color='k', lw=1) ax.axvline(180, color='k', lw=1) ax.set(xticks=range(0, 361, 60), yticks=range(0, 361, 60), xlabel=r"$\chi_1$", ylabel=r"$\chi_2$") degree_formatter = plt.matplotlib.ticker.StrMethodFormatter( r"{x:g}$\degree$") ax.xaxis.set_major_formatter(degree_formatter) ax.yaxis.set_major_formatter(degree_formatter) if ref: X, Y = np.meshgrid(np.arange(0, 360, 6), np.arange(0, 360, 6)) levels = [1, 6, 600] colors = ['#A1D4FF', '#35A1FF'] ax.contourf(X, Y, np.load(Janin_ref), levels=levels, colors=colors) a = self.results.angles.reshape(np.prod( self.results.angles.shape[:2]), 2) ax.scatter(a[:, 0], a[:, 1], **kwargs) return ax