Good afternoon,

I am trying to model missing residues into my crystal structure following the method on the website: https://salilab.org/modeller/wiki/Missing_residues. I am also trying to restrain the crystal coordinates so that only missing residues move (and the rest of the original crystal coordinates remain the same) during refinement using the select_atoms method. However when I compare my final models produced by my script to my original crystal structure, I find that the side chains of several amino acids three of four amino acids away from the missing residues have been flipped. How can I ensure that only the missing residues are refined and the crystal coordinates remain the same? I am wondering if I’ve missed something important out of my script. See my script below.

Many thanks.

from modeller import * # Load standard Modeller classes

from modeller.automodel import * # Load the AutoModel class

log.verbose() # Create log file

env = Environ()

# directories for input atom files

env.io.atom_files_directory = ['.', '../atom_files']

env.io.water = True

# Only refine/move missing residues - restrain crystal coordinates

class MyModel(LoopModel):

#picks residues to be refined by loop modelling

def select_loop_atoms(self):

#refines residue ranges defined simultaneously

return Selection(self.residue_range('5:A', '13:A'),

self.residue_range('99:B', '105:B'),

self.residue_range('251:D', '256:D'))

# redefine the special_patches routine to include additional disulfides

def special_patches(self,aln):

self.patch(residue_type='DISU',residues=(self.residues['26:A'],self.residues['199:C']))

self.patch(residue_type='DISU',residues=(self.residues['29:A'],self.residues['201:C']))

a = MyModel(env, alnfile = 'alignment.ali', # alignment file

knowns = 'xxx', # aa sequence of original template - crystal coordinates

sequence = 'xxx_fill', # aa sequence of original template with missing residues filled in

loop_assess_methods = (assess.DOPE,

assess.DOPEHR,

assess.GA341))

a.starting_model= 1             # Index of the first model

a.ending_model  = 1             # Index of the last model

a.loop.starting_model = 1       # First loop refined model

a.loop.ending_model = 10        # Last loop refined model

a.loop.md_level = refine.fast   # Loop model refinement level

a.make()                        # Do modelling