Fix Backbone Atoms
set all [atomselect top all]
set to_fix [atomselect top “protein and backbone”]
$all set beta 0
$to_fix set beta 1
$all writepdb fix_backbone.pdb
Restrain CA Atoms
set all [atomselect top all]
set sel [atomselect top “protein and name CA”]
$all set beta 0
$sel set beta 0.5
$all writepdb restrain_ca.pdb