Mutate_1st (080218)
O has had commands to mutate the sequence of a molecule for many years. The Mutate_insert command, in particular, adds a new residue after a particular residue in the molecule. This makes it hard to place a new residue at the beginning of the molecule (although it can be done). Mutate_1st is the command you need to insert residues at the beginning of a molecule, but is otherwise very similar to mutate_insert. In particular, this commands only makes space in the various O DBs for the new residue(s), you have to do something about placing the atoms at some sensible place (e.g. with the Grab_build command). For each new residue, the user needs to specify a residue name (e.g. A0) and the residue type (e.g. PHE). All objects associated with the molecule are deleted.
O > mut_1st
Mut> Mutate a molecule by inserting residues at the start
Mut> Molecule ([A ]) :
Mut> New residue name and type (<cr> to end) : a0 phe
Mut> New residue name and type (<cr> to end) :
Mut> There are 1 mutations
Mut> This atom has the potential for an incorrect Z: CA
Mut> SEGIDs will be checked and updated
Mut> Cannot find a segid
Mut> Molecular connectivity deleted.
Mut> Stereochemistry entries deleted
Mut> Delete_objec CA A ;
done
where the new residue is a phenylalanine, called A0. The molecule has no segIDs associated with it. The stereochemistry is generated by activating the @on_stereo_chem macro in the database.
Mutate_delete
mutate_delete <molecule> <residue_name>i
Any number of residues can be deleted. Input is terminated by a blank input.
This command would usually leave non-standard stereochemistry. This can be corrected with refi_zone, lego_loop or Grab commands.
Mutate_insert
mutate_insert <molecule> <residue_name>
<new_residue_name new_residue_type>i
Adds new residues after a specified place in the molecule. Terminated by a blank line. The new residue names should be unique to the molecule.
This command merely makes space in the database for new residues. The user must place them. This could be done in a number of ways, but recommend lego_loop to start with
E.g. The following will insert an alanine residue after residue 102 in molecule A26:
mut_insert a26 102 102a ala ;
sel_off a26 102 103
lego_loop a100 a105
If the new residue had a longer side chain e.g. PHE it would also need to be constructed with lego_side and identify an atom.
Note that this command does not allow one to add new residues at the start of a molecule. This is done with the mutate_1st command.
Mutate_replace
mutate_replace <molecule> <residue_name new_residue_type>i
Any number of residues can be mutated until a blank line is entered. All atom properties of the specified molecule are changed in size to accommodate the new sequence. Certain properties are assigned special values, others are given default values.
_atom_z is changed to reflect the elemental type of the new atom
_atom_b new atoms have a temperature factor of 20.Å2
_atom_name new atom names are taken from the contents of the file specified in the last Connect_file command.
_atom_wt new atoms have weights of 1.0
_atom_colour all atoms in a mutated residue are coloured magenta
The default values for all other properties are 0,0.0 and ' ' for integer, real and character properties.
The new residue type must exist as an entry in the contents of the file specified in the last Connect_file command.
Because molecular objects are described in the database as link lists, their pointers are to the OLD positions in the molecule. All objects of the changed molecule are therefore deleted and must be re-made by the user. Mutated residues will appear coloured magenta.
Side chain confirmations are from the most frequent side chain rotamer. The database must therefore be correctly defined in the stereochemistry dictionary
Here is an example:
O > mut_repl
Mut> Mutate a molecule by replacing one residue type
Mut> by another.
Mut> Molecule ([TRACE ]) : a
Mut> Residue name and new type (<cr> to end) : a7 leu
Mut> Residue name and new type (<cr> to end) : a8 phe
Mut> Residue name and new type (<cr> to end) :
Mut> There are 2 mutations
Mut> Molecular connectivity deleted.
Mut> Stereochemistry entries deleted
Mut> Delete_objec ACA AALL ;
Refi > No bond distances in Db for FA
Refi > No bond angles in Db for FA
Refi > No torsion_fixed in Db for FA
Refi > No torsion_flexible in Db for FA
O > wr @on_mutate ;;
@ON_MUTATE T 4 60
Refi_init A
Refi_generat ; ;
Build_rotome A A7 1
Build_rotome A A8 1
The strereochemistry entries for the molecule are also automatically deleted.A macro on_mutate is generated in the user's database and activated. This macro (see above) builds a simple set of stereochemistry entries and then carries out the necessary rotamer builds. The warning messages ('No bond ...') occur because the molecule (the P2 distributed coordinates) has a fatty acid for which no stereochemistry information exists.