Dear all,

I am trying to construct a model with four HIS binding to a copper. I set the distance constraints for ND1--CU as 2.0 angstrom, but the distances between ND1 and CU of the constructed models are around 2.5 angstrom, it seems that the constraints failed. Acctually, when I checked the model, I found that the distances could be around 2.0 angstrom if CU was just moved a little bit.

        rsr.add(forms.gaussian(group=physical.xy_distance,
                               feature=features.distance(at['ND1:13:X'],at['CU:43:Y']),
                               mean=2.00, stdev=0.05))
        rsr.add(forms.gaussian(group=physical.xy_distance,
                              feature=features.distance(at['ND1:14:X'],at['CU:43:Y']),
                               mean=2.00, stdev=0.05))

Could someone tell  me what kinds of reasons could result in restraints failure? Thanks very much!


All the best,
Qinghua