[phenixbb] Glycan Links/Restraints

[Damian Ekiert]

Sorry to bring up an old topic again but I can't find any documentation of glycan refinement on the Phenix website and previous threads don't seem to answer my question.

I am refining a structure with N-linked glycans.  I have inserted several "apply_cif_link" records to my .eff file to define the glycan topologies (see below) and fed in a cif file for BMA.  After fiddling for quite some time now, I have managed to get around all the error messages people have described previously to disappear.  Yet, 1) none of my linkages appear to be enforced and 2) even the restraints on the individual sugars appear to be unenforced (or at least, insufficiently so).  For example, some rings are rendered almost flat, or flipped into boat or otherwise distorted conformations, and glycosidic bonds stretch to >2 A.

No obvious signs of trouble in the log file, running the latest version (1.7, also tried 1.6.4), but my glycans look terrible (despite some of the best density I have ever seen!  :-)  )

Any suggestions would be appreciated!

Thanks,

Damian Ekiert



>From my .eff file:

    apply_cif_link {
      data_link = NAG-ASN
      residue_selection_1 = chain X and resname NAG and resid 401
      residue_selection_2 = chain A and resname ASN and resid 91
    }
    apply_cif_link {
      data_link = NAG-ASN
      residue_selection_1 = chain Y and resname NAG and resid 401
      residue_selection_2 = chain C and resname ASN and resid 91
    }
    apply_cif_link {
      data_link = NAG-ASN
      residue_selection_1 = chain Z and resname NAG and resid 401
      residue_selection_2 = chain E and resname ASN and resid 91
    }
    apply_cif_link {
      data_link = BETA1-4 
      residue_selection_1 = chain X and resname NAG and resid 402
      residue_selection_2 = chain X and resname NAG and resid 401
    }
    apply_cif_link {
      data_link = BETA1-4 
      residue_selection_1 = chain Y and resname NAG and resid 402
      residue_selection_2 = chain Y and resname NAG and resid 401
    }
    apply_cif_link {
      data_link = BETA1-4 
      residue_selection_1 = chain Z and resname NAG and resid 402
      residue_selection_2 = chain Z and resname NAG and resid 401
    }
    apply_cif_link {
      data_link = BETA1-4 
      residue_selection_1 = chain Y and resname BMA and resid 403
      residue_selection_2 = chain Y and resname NAG and resid 402
    }
    apply_cif_link {
      data_link = ALPHA1-3
      residue_selection_1 = chain Y and resname MAN and resid 404
      residue_selection_2 = chain Y and resname BMA and resid 403
    }