charmm_segment_topology.h

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/**
 * \file IMP/atom/charmm_segment_topology.h
 * \brief Classes for handling CHARMM-style topology of segments.
 *
 * Copyright 2007-2021 IMP Inventors. All rights reserved.
 *
 */

#ifndef IMPATOM_CHARMM_SEGMENT_TOPOLOGY_H
#define IMPATOM_CHARMM_SEGMENT_TOPOLOGY_H

#include "IMP/Object.h"
#include "Hierarchy.h"
#include <IMP/atom/atom_config.h>
#include "charmm_topology.h"
#include "CHARMMParameters.h"

IMPATOM_BEGIN_NAMESPACE

//! The topology of a single CHARMM segment in a model.
/** CHARMM segments typically correspond to IMP::atom::Chain particles.
 */
class IMPATOMEXPORT CHARMMSegmentTopology : public IMP::Object {
  /** @name Residues

      The segment contains a chain of residues.
   */
  /**@{*/
  IMP_LIST_ACTION(public, CHARMMResidueTopology, CHARMMResidueTopologies,
                  residue, residues, CHARMMResidueTopology *,
                  CHARMMResidueTopologies, obj->set_was_used(true), , );
  /**@}*/

  IMP_OBJECT_METHODS(CHARMMSegmentTopology);

 public:
  CHARMMSegmentTopology(std::string name = "CHARMM segment topology %1%")
      : Object(name) {}

  //! Apply patches to the first and last residue in the segment.
  /** Default patches are defined for each residue type in the topology
      file. For example, segments containing amino acids will by default
      apply the CTER and NTER patches to the C and N termini, respectively.
   */
  void apply_default_patches(const CHARMMParameters *ff);
};

IMP_OBJECTS(CHARMMSegmentTopology, CHARMMSegmentTopologies);

//! The topology of a complete CHARMM model.
/** This defines all of the segments (chains) in the model as
    CHARMMSegmentTopology objects, which in turn define the list of residues,
    the atoms in each residue, and their types and the connectivity
    between them.

    A CHARMMTopology object can be created manually, in which case add_segment()
    can be called to add individual CHARMMSegmentTopology objects. In this way
    a new topology can be created, e.g. from protein primary sequence.

    Alternatively, given an existing Hierarchy, e.g. as returned from
    read_pdb(), CHARMMParameters::create_topology() can be called to generate
    a new topology that corresponds to the primary sequence of the Hierarchy.

    A new topology can be patched (apply_default_patches() or
    CHARMMPatch::apply()) to modify the simple chain of residues to
    account for modified residues, C- or N-termini special cases, disulfide
    bridges, etc.

    Once a topology is created, it can be used to generate new particles
    which conform to that topology (create_hierarchy()), or to add
    topology information to an existing Hierarchy (e.g. add_atom_types(),
    add_bonds(), add_charges()).
 */
class IMPATOMEXPORT CHARMMTopology : public IMP::Object {
public:
  typedef std::map<const CHARMMResidueTopology *, Hierarchy> ResMap;
private:
  Pointer<const CHARMMParameters> force_field_;
  WarningContext warn_context_;

  void map_residue_topology_to_hierarchy(Hierarchy hierarchy,
                                         ResMap &resmap) const;

 public:
  CHARMMTopology(const CHARMMParameters *force_field,
                 std::string name = "CHARMM topology %1%")
      : Object(name), force_field_(force_field) {
    set_was_used(true);
  }

  const CHARMMParameters *get_parameters() { return force_field_; }

  //! Add a sequence (as a string of one-letter codes) to the topology.
  /** The sequence can contain amino-acid one-letter codes and '/' characters
      to denote the start of a new segment. The empty string simply adds a new
      segment that contains no residues.
      \exception ValueException if an invalid one-letter code is passed.
   */
  void add_sequence(std::string sequence);

  //! Call CHARMMSegmentTopology::apply_default_patches() for all segments.
  void apply_default_patches() {
    for (unsigned int i = 0; i < get_number_of_segments(); ++i) {
      get_segment(i)->apply_default_patches(force_field_);
    }
  }

  //! Create a new Hierarchy in the given model using this topology.
  /** The hierarchy contains chains, residues and atoms as defined in the
      topology. Note, however, that none of the generated atoms is given
      coordinates.
      Chains are labeled 'A', 'B' etc. Residues are numbered from 1 within
      each chain.
      \see add_coordinates.
   */
  Hierarchy create_hierarchy(Model *model) const;

  //! Add CHARMM atom types to the given Hierarchy using this topology.
  /** The primary sequence of the Hierarchy must match that of the topology.
      A warning will be printed for any atoms that cannot be found in the
      topology (and no CHARMM atom type will be assigned). Any atoms that
      already have a CHARMM atom type and that are present in the topology
      will have that type reassigned.
      \see CHARMMAtom.
   */
  void add_atom_types(Hierarchy hierarchy) const;

  //! Add atom Cartesian coordinates to the given Hierarchy using this topology.
  /** The primary sequence of the Hierarchy must match that of the topology.

      This method can be used to add missing coordinates (e.g. of hydrogens
      or sidechains, such as those added by add_missing_atoms()), or to
      generate a starting conformation for a new Hierarchy (e.g. generated
      by create_hierarchy()). On exit, all atoms will have coordinates.

      - Cartesian coordinates for any atoms that are not currently core::XYZ
        particles are generated using internal coordinates that relate them
        to particles that do have XYZ coordinates.

      - For each segment (chain), if no atoms have coordinates but a triplet
        of atoms can be found where their internal distances and angle can be
        determined from internal coordinates, these three atoms will be
        placed to seed the generation procedure. For the first segment, the
        atoms will be placed on the xy plane with the first atom at the origin.
        For subsequent segments, the first atom is placed offset by (2.,2.,2.)
        from the last atom in the previous segment.

      - If any atoms cannot be placed using either method, their coordinates
        are assigned randomly to lie near atoms that are near in sequence or,
        if no such atoms exist, near the segment origin.

      \note It is valid to specify internal coordinates in a CHARMM topology
            file that leave the angles or distances unspecified. This function
            will attempt to fill in this missing information using CHARMM atom
            types and the parameter file. Thus, better results will be obtained
            if add_atom_types() is called before this function, and the
            CHARMMParameters object used contains parameter information.
   */
  void add_coordinates(Hierarchy hierarchy) const;

  //! Add any missing atoms to the given Hierarchy using this topology.
  /** Missing atoms are defined as those present in the topology but not
      in the hierarchy.
      Newly-added atoms are assigned CHARMM types, but no coordinates
      (use add_coordinates() to add them).
      The primary sequence of the Hierarchy must match that of the topology.
      \see CHARMMAtom, remove_charmm_untyped_atoms, add_coordinates.
   */
  void add_missing_atoms(Hierarchy hierarchy) const;

  //! Make the Hierarchy conform with this topology.
  /** The hierarchy is modified if necessary so that each residue contains
      the same set of atoms as defined in the CHARMM topology, and any
      atoms missing coordinates are assigned them.

      This is equivalent to calling add_atom_types(), add_missing_atoms(),
      remove_charmm_untyped_atoms(), and add_coordinates() in that order.
   */
  void setup_hierarchy(Hierarchy hierarchy) const;

  //! Add CHARMM charges to the given Hierarchy using this topology.
  /** The primary sequence of the Hierarchy must match that of the topology.
      \see Charged.
   */
  void add_charges(Hierarchy hierarchy) const;

  //! Add bonds to the given Hierarchy using this topology, and return them.
  /** The primary sequence of the Hierarchy must match that of the topology.
      Parameters for the bonds (ideal bond length, force constant) are
      extracted from the CHARMM parameter file, using the types of each atom
      (add_atom_types() must be called first, or the particles otherwise
      manually typed using CHARMMAtom::set_charmm_type()).

      If no parameters are defined for a given bond, the bond is created
      with zero stiffness, such that the bond can still be excluded from
      nonbonded interactions but BondSingletonScore will not score it.

      Note that typically CHARMM defines bonds and impropers
      (see add_impropers()) but angles and dihedrals are auto-generated from
      the existing bond graph (see CHARMMParameters::create_angles() and
      CHARMMParameters::create_dihedrals()).

      The list of newly-created Bond particles can be passed to a
      StereochemistryPairFilter to exclude bonded particles from nonbonded
      interactions, or to a BondSingletonScore to score each bond.

      \return a list of the generated Bond decorators.
   */
  Particles add_bonds(Hierarchy hierarchy) const;

  //! Add dihedrals to the given Hierarchy using this topology, and return them.
  /** The primary sequence of the Hierarchy must match that of the topology.

      Typically, dihedrals are auto-generated from the existing bond
      graph (see CHARMMParameters::create_dihedrals()) rather than using
      this function.

      \return a list of the generated Dihedral decorators.

      \see add_bonds().
   */
  Particles add_dihedrals(Hierarchy hierarchy) const;

  //! Add impropers to the given Hierarchy using this topology, and return them.
  /** The primary sequence of the Hierarchy must match that of the topology.

      The list of newly-created Dihedral particles can be passed to a
      ImproperSingletonScore to score each improper dihedral.

      \return a list of the generated Dihedral decorators.

      \see add_bonds().
   */
  Particles add_impropers(Hierarchy hierarchy) const;

  /** @name Segments

      The topology contains a list of segments, one for each chain.
   */
  /**@{*/
  IMP_LIST_ACTION(public, CHARMMSegmentTopology, CHARMMSegmentTopologies,
                  segment, segments, CHARMMSegmentTopology *,
                  CHARMMSegmentTopologies, obj->set_was_used(true), , );
  /**@}*/

  IMP_OBJECT_METHODS(CHARMMTopology);
};
IMP_OBJECTS(CHARMMTopology, CHARMMTopologies);

IMPATOM_END_NAMESPACE

#endif /* IMPATOM_CHARMM_SEGMENT_TOPOLOGY_H */