NAME
     Hbond - locate possible hydrogen bonds in a protein
     structure

SYNOPSIS
     hbond -options files

DESCRIPTION
     Hbond is a program to read in Brookhaven format files and to
     calculate all the possible hydrogen bonds and other
     sidechain interactions of interest. The output from hbond is
     a file with a .hbd extension that is primarily meant to be
     used as input for joy.  If you want to use the file for
     other purposes it is important that you understand the
     assumptions used to define the hydrogen bonds.  It is your
     responsibility to make sure that the input Brookhaven file
     is o.k., i.e.  it should not have alternate atoms, explicit
     hydrogen atoms, etc; preprocessing of the Brookhaven file
     with pdb2atm(1) is recommended.

     The following options to hbond are available:

     -h   Print a help message on the standard output.

     -v   Be verbose in what is reported to the user, this is
          mainly of use to see what is actually being read by
          hbond.

     -V   Print the version number of hbond on the standard
          output.

WHAT IS A HYDROGEN BOND ?
     In the interests of simplicity, a hydrogen bond (or
     analogous interaction) is flagged if the distance between
     the two participants in the interaction are less than a set
     distance apart (usually 3.5). For disulphide bonds the
     criteria is that the two sulphur atoms are less than 3.0
     apart (note, this is a generous cutoff). Due to the larger
     Van der Waal's radius of sulphur atoms a 4.0 cutoff is used
     for interactions involving this element type.  No check is
     made on the lower bound of the distance.  Interactions to
     HETATM records are always calculated.  Some interactions
     also have the relevent angles calculated, however this has
     no influence as to whether an atom pair occurs in this file
     (and is considered as a hydrogen bond). Note that angles
     that are undefined are written as 999.99.

     For mainchain to mainchain hydrogen bonds, energies are
     calculated as in the paper of Kabsch and Sander.

     The following points may need to be considered before you
     use the program.  The first is that the amide sidechains of
     asparagine and glutamine are assumed to be undetermined (
     i.e.  you can swap the NH2 and O atoms freely), thus both
     atoms are considered as donors and acceptors. The second
     point is that the y atom of cysteine is considered to be a
     possible donor and acceptor atom, additionally the d sulphur
     of methionine is an acceptor. Finally, the protonation state
     of an acidic residue (aspartic acid and glutamic acid is
     considered as undefined), i.e.  it can be protonated and so
     again either of the oxygen atoms can be both donors and
     acceptors. Finally, (again) no interactions between residues
     are considered for atoms in residues closer than two
     residues from the central residue.

     Because of the nature of the cutoff, it is likely that not
     all the interactions reported are likely to be real hydrogen
     bonds. However, the definition is rigid and easily
     defendable. Other methods are likely to produce lists of
     hydrogen bonds that are simply subsets of the ones reported
     by hbond.  However, it is relatively easy either to write a
     program that will select out the hydrogen bonds from the
     .hbd file, or to change the cutoffs internally within the
     program.

FORMAT OF THE .hbd FILE
     The .hbd file contains a small header, whether HETATM
     records were included in the analysis.  There the follows a
     list of the possible interactions, listed one per line, with
     the donor listed first followed by the acceptor atom.  The
     format for the data in the .hbd file is (FORTRAN format):
     1X, I3, 1X, A5, 1X, A1, 1X, A, 1X, A3, 1X, I3, 1X, A5, 1X,
     A1, 1X, A, 1X, A3, 1X, A3, 1X, I4, 1X, F4.2, 1X, F4.2, 1X,
     F6.2, 1X, F6.2

     Where the fields are; the index of the first residue, the
     number of the donor residue, the chain-name of the donor
     residue, the residue type of the donor residue, and the atom
     type of the donor atom; this is followed by a similar set of
     values for the acceptor atom. This information is followed
     by the class of the hydorgen bond (see table below), an
     integer indicating the soacing of the donor and acceptor
     atoms (can be negative), the distance between the donor and
     acceptor atoms, the distance between the hydrogen atom and
     the acceptor (see below for how hydrogen positions are
     calculated), the angle between the donor, hydrogen and
     acceptor and finally the angle between the donor, acceptor
     and carbonyl carbon. An example of a .hbd file is:
     # produced by hbond, version 1.0c (2.3b)
     #   parameterized for  600 residues, 20 atoms per residue, and  500 hetatoms
     #
     # coordinate data taken from file 2ptn.atm
     #   number of atoms    =  1610
     #   number of residues =   221
     #   number of chains   =     2
     #                        chain  1 extent from    1 to    4, of length   5
     #                        chain  2 extent from    5 to  221, of length 216
     #   number of hetatoms =     1
     #
     # criteria for hydrogen bond definition :-
     #  donor-acceptor distance cutoff (oxygen and nitrogen) = 3.50
     #  donor-acceptor distance cutoff (sulphur)             = 4.00
     #  hydrogen-acceptor distance cutoff                    = none
     #  angular criteria applied                             = none
     #  energy criteria applied                              = none
     #  include HETATM records                               =    T
     #  include WATER records                                =    T
     #
     #----- Donor ----- ---- Acceptor ---          ------- Geometry ------ - Energy -
     #index - res - atm index - res - atm typ span Dd-a Dh-a <d-H-N <a-O=C   kJ/mol
        1   16    I N   120  142    G O   MM   119 3.29 9.99 999.99 999.99   999.99
        1   16    I N   121  143    N O   MM   120 3.03 9.99 999.99 999.99   999.99
        1   16    I N   174  194    D OD1 SN   173 2.72 9.99 999.99 120.26 * 999.99
        1   16    I N   174  194    D OD2 SN   173 3.48 9.99 999.99  81.36 * 999.99
        2   17    V N   169  189    D O   MM   167 2.82 1.85 166.93 166.76    -3.01
        4   19    G N     2   17    V O   MM    -2 3.42 3.40  83.36  71.35      .97
        5   22    C N   133  155    L O   MM   128 3.08 9.99 999.99 999.99   999.99
        5   22    C SG  133  155    L O   SO   128 3.52 9.99 999.99  89.43   999.99
        5   22    C SG  134  156    K O   SO   129 3.41 9.99 999.99  75.51   999.99
        5   22    C SG  135  157    C SG  DS   130 2.04 9.99 999.99 999.99   999.99

     The hydrogen bonds are classified using the following scheme:
     center;
     l    l.
     class     meaning
     MM   mainchain to mainchain
     MH   mainchain to hetero atom
     MW   mainchain to water
     SO   sidechain to mainchain CO
     SN   sidechain to mainchain NH
     SS   sidechain to sidechain
     SH   sidechain to hetero atom
     SW   sidechain to water
     DS   disulphide

CAVEATS
     Please bear in mind what the program is meant to do, before
     blindly using its output. The program is likely to be
     changed in the near future. The main limit you are likely to
     encounter is a maximum numer of residues of 500.

SEE ALSO
     pdbseq(1), joy(1).

RELEASE LEVEL
     This document describes hbond version 0.7 and later.