CHARMM c28a3 rtop.doc

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                            Residue Topology File

                    By Alexander D. MacKerell Jr., August 1999

        This section of the documentation describes the contents of the
topology file and a listing of the current topology files available to
the users.  CHARMM topology files contain the information necessary to
describe bond connectivity, angle, dihedral angle and improper
dihedral angle content, charge distribution, hydrogen-bond donors and
acceptors and internal coordinate information.  Thess data are required
by CHARMM in order to determine energies, perform energy minimizations
and molecular dynamics simulations as well as perform other various
structural manipulations.  Documentation concerning implementation of
a topology file in order to build a structure is contained in

* Menu:

* Overview::      Overview of CHARMM Topology File
* RTFDATA::       Description of Topology Files available for general use

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                      Overview of CHARMM Topology File

        An example of a topology file is given below followed by
a description of the content of the various sections. Also see
IO.DOC for information on the individual keywords.

(A)   * CHARMM example topology file
(B)      19    1
(C)   MASS    1  H    1.00800 H
      MASS    2  O   15.99900 O
(D)   DECL -C
      DECL -O
      DECL +N
      DECL +H
      DECL +CA
(G)   RESI GLY      0.000
(G1)  GROUP 
(G2)  ATOM N    NH1    -0.35
      ATOM H    H       0.25
      ATOM CA   CH2E    0.10
      ATOM C    C       0.55
      ATOM O    O      -0.55
(G3)  BOND N    CA        CA   C         C    +N        C    O         N    H
      DOUBLE CA   CB
      TRIPLE CB   CG
(G4)  ANGL  N   CA   C  (and so on)
(G5)  DIHE -C   N    CA   C         N    CA   C    +N        CA   C    +N   +CA
(G6)  IMPH N    -C   CA   H
(G7)  DONO  H   N
(G8)  ACCE  O  C
(G9)  IC   -C   CA   *N   H      0.0000    0.00  180.00    0.00   0.0000
      IC   -C   N    CA   C      0.0000    0.00  180.00    0.00   0.0000
      IC   N    CA   C    +N     0.0000    0.00  180.00    0.00   0.0000
      IC   +N   CA   *C   O      0.0000    0.00  180.00    0.00   0.0000
      IC   CA   C    +N   +CA    0.0000    0.00  180.00    0.00   0.0000
      IC   N    C    *CA  CB     0.0000    0.00  120.00    0.00   0.0000
(H)   PRES CTER      -1.000
(H2)  ATOM C    C       0.14
      ATOM OT1  OC     -0.57
      ATOM OT2  OC     -0.57
(H3)  BOND C    OT1       C    OT2
      ANGL OT1  C   OT2  (and so on)
      DIHE N    CA    C    OT2
      IMPH C    CA    OT2  OT1
(H4)  ACCE  OT1 C
      ACCE  OT2 C
      IC   N    CA    C    OT2    0.0  0.0  180.0  0.0  0.0
      IC   OT2  CA    *C   OT1    0.0  0.0  180.0  0.0  0.0
(I)   END

        The topology file starts with the title (A) which contains
information on the origins and applicability of that file.  This is
directly followed by (B) the CHARMM version number under which that
particular file was developed.

        Section (C) contains the various atom types used in the
topology file and is signified by the keyword MASS.  Information
includes a number associated with each atom type, the atom type
followed by the mass of the atom.  The final column is the atomic type
and is included for compatibility with the MMFF code.  The number of
each atom type is used in conjunction with the parameter file (see
PARMFILE.DOC) and is the marker for the various energy term arrays
(bonds, angles etc.)

        Section (D), signified by DECLare, prescribes which atoms will
be selected from the previous or next residue when covalently linking
residue together as in the connection of residues in a polypeptide via
a peptide bond linkage.

        Section (E) contains the DEFAult patches used on the FIRSt and
LAST residues in a generated segment (i.e. the NTERminus and CTERminus
of a polypeptide chain, see section (G10).  (F) Next are the
AUTOgenerate default options to be used when building a sturcture.
AUTO ANGLes specifies that all possible angles and DIHEdral specifies
that all possible dihedral angles be generated when building a
structure.  If these options are not included the angles and/or
dihedrals must be listed explicitly in the topology file (see G4 and G5).

        Designation of the various residues, nucleotides etc. is done
using the (G) RESIdue keyword followed by the residue name (four
characters) and the total charge of the residue.  A residue may then
be subdivided into (G1) GROUps, which contain several atoms whose total
charge is neutral or a unit charge.  This subdivision is used in the 
calculation of nonbonded interactions using the group keyword and in
the extended electrostatics options (see NBONDS.DOC).  Next are the
individual ATOM specifications which include the IUPAC atom name, the
atom type and the charge of that atom.  In certain cases 1 or more
atom names will follow the charge which indicate atoms which are to be
excluded from nonbond calculations with that particular atom (i.e.,
used to exclude atoms in rings from seeing each other in topologies
prior the CHARMM22 releases).

        Following the various atoms are the (G3) BOND connectivites,
the (G4) ANGLe, the (G5) DIHEdral and (G6) IMPRoper dihedral listings.
The BOND listings are always required in order to define the
connectivity of the molecule; BOND can be replaced by DOUBLE, TRIPLE
or AROMATIC allowing for compatibility with MMFF.  The ANGLe and/or
DIHEdral listings should be omitted if the AUTOgenerate ANGL and/or
DIHEdral options are being used.  It should be remembered that
autogeneration works in conjunction with the GENErate command; in
PATChes invoked after the initial structure generation the
AUTOGENERATE command must be invoked following the patch to create the
angle and dihedral lists or the angles and dihedrals must listed
explicitly in the patch.  Note that problems will be encountered if
autogeneration is performed with water molecules present. IMPRoper
dihedrals are only included in special cases and must be listed
explicitly.  Note that the improper atom order should place the
central atom first.

        For making hydrogen bond lists the (G7) DONOr and (G8) ACCEptors
must be listed.  These listings include the donor and donor antecedent
and the acceptor and acceptor antecedent atom names.  The antecedents
are required if hydrogen bond angle cutoffs are being invoked (see
HBONDS.DOC).  If only the hydrogen bond distance criteria are desired,
as with the amber force field, the antecedents should be omitted and
the BLNK inserted prior to the donor atom name (e.q. DONO BLNK H1 and
ACCE O2).  Section (G9) contains the internal coordinate information
(IC or BILD) which may be used to build a molecule or add missing 
atoms, such as hydrogens to a crystal structure (see IO.DOC and

        The next line (G10) contains the PATChes to the FIRSt and LAST
atoms of the residue and is required on when the DEFAult (E) is to 
be overridden.

        Along with RESIdues the topology also contains patch residues,
(H) PRES, which may be used at the termini of a structure, alter a
RESIdue structure or form covalent links between residues (e.g.
disulfide bridges).  PRESidues may be used in either a GENErate or
PATCh statement (see STRUCT.DOC).  In addition to the contents of the
standard RESIdue atoms may also be (H1) DELEted (see IO.DOC) from a
residue.  Atoms already specified in the initial residue may be
respecified in order to change the atom type or CHARGE.  The GROUp
option may also be included to alter the group lists.  Again (H3) BOND
and IMPRoper listings must be included.  The ANGLe and DIHEdral
listings only need to be included if the AUTOgenerate option is not
used OR if the PRES is used in a PATCh statement.  Finally, (H4) a
PRES may specify new DONOrs and ACCEptors and new IC or BILD

        Exiting the topology file is done with the (I) END command.

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          Description of Topology Files Available for general use

    (1)  top_all22_prot.inp       all hydrogen RTF for proteins
    (2)  top_all22_model.inp      all hydrogen RTF for protein model cmpds
    (3)  top_all22_sugar.rtf      all hydrogen RTF for sugars
    (4)  top_all27_na.rtf         all hydrogen RTF for nucleic acids
    (5)  top_all27_lipid.rtf      all hydrogen RTF for lipids
    (6)  top_all27_na_lipid.rtf   all hydrogen RTF for nucleic acids and lipids
    (7)  top_all27_prot_na.rtf    all hydrogen RTF for proteins and nucleic acids
    (9)  top_all27_prot_lipid.rtf all hydrogen RTF for proteins and lipids
    (9)  toph19.inp               extended atom RTF for proteins
    (10) toprna10r_22.inp         extended atom RTF for nucleic acids

        Topology files for proteins and nucleic acids currently exist
using both all-hydrogen and extended atom representations.  The most
recent topologies are the all-hydrogen sets for proteins,
TOP_ALL22_PROT.INP, nucleic acids, TOP_ALL27_NA.RTF, and lipids,
TOP_ALL27_LIPID.RTF.  The extended atom protein, TOPH19.INP, and
nucleic acid, TOPRNA10R_22.INP, topologies are from the Version 19
release.  Alterations in the dihedrals have been made to
TOPRNA10R_22.INP to reproduce the original results, however, due to
the small increase in the number of atoms upon going from the extended
to all-hydrogen representations in nucleic acids it is recommeded that
TOP_ALL27_NA.RTF be used.  The all-hydrogen sugar parameters,
TOP_ALL22_SUGAR.RTF, are being developed by John Brady.  It is
expected that additional residues will be added in the future.  As of
the c27b1/c28a1 release new topology files for lipids and nucleic
acids (all27) were included and the old all22 files have been removed.
The obsolete all22 files can be found in the toppar_history
	For more information, including references, see PARAMETERS
portion of the documentation.

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