Hello,
I am trying to create a model of a protein using 3 different
templates. The first template covers about 1/3 of the protein, the
second covers the central part of the model protein and the third
overlaps with the second with an additional extension to cover the c-
terminus of the protein. The templates' crystal structures have
incorporated metal ions and other ligands, which i would like to
transfer into the model. Unfortunately i cannot seem to make this work
using the script for introducing HETATM ligands into the model. I have
created the alignment file and added '.' into both the template and
into the sequence alignment. The PDB has the HETATM ligands at the end
of the sequence, so i have added them at the end of the alignment
file, as suggested in the manual. However, since three different
templates are being used, only parts of which overlap, introducing '.'
at the end of the model sequence does not work, because it does not
align with the template. On the other hand adding '.' into the model
sequence, the way it would align with the template, disturbs the
structure, disrupting the alignment with the other templates and
causing a break in the peptide. I tried adding gaps for each ligand in
the other templates, but this does not help. I have tried creating
part of the model with just one template and the aligning sequence
from my protein of interest. In that situation the ligands are easily
added. Is there any remedy to my problem in modeller that i have not
considered?
here is the script i am using for introducing HETATM ligands into the
model
# Homology modeling with ligand transfer from the template
from modeller import * # Load standard Modeller classes
from modeller.automodel import * # Load the automodel class
log.verbose() # request verbose output
env = environ() # create a new MODELLER environment to build this
model in
# directories for input atom files
env.io.atom_files_directory = ['.', '../atom_files']
# Read in HETATM records from template PDBs
env.io.hetatm = True
a = automodel(env,
alnfile = '1-78-40-clmpldr4.ali', # alignment filename
knowns=('1M55','1U0J','1SXJ'), # codes of
the templates
sequence = 'B25') # code of the target
a.starting_model= 1 # index of the first model
a.ending_model = 1 # index of the last model
# (determines how many models to
calculate)
a.make() # do the actual homology modeling
Violetta Kivovich
MD/PhD Candidate G4
vzk102(a)psu.edu