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The keyword script Eckhard mentioned did the job I wanted to achieve. I created the cif file for my ligand through the Monomer Library Stetcher and then edited torsion angle part to include the restraint for the OH tiling angle. I am running the CCP4 Suite 6.0.2 and CCP4i 1.4.4.2. but I still have to include an external keyword script restr tors include resi XXX to impose torsion angle restraint on the ligand. With the script read in I can further adjust the Overall wt for Torsion under Geometric parameters menu to achieve a geometry that best fits to the density. I have tried weighting term 0.05 or 0.08 for this case. The smaller weight at 0.05 gave me better planarity for the aromatic residues without sacrifying too much in R/R-free (only 0.1% lower with 0.08 weight). Thanks again for suggestions from many others. Huiying On Fri, 5 Dec 2008, Eckhard Hofmann wrote: > Hi Huiying, > could you tell us which version of refmac you are using? > There has been an issue with torsion definitions in ligands NEVER included in > the refinement, even if they were in the cif (at least up to > Refmac_5.2.0019). I did have the same effect you had and wondered why. (See > list in October 2007) > > Garib modified the code in a later version of 5.4 to allow you to include all > torsions from one residues by applying the following line: > > restr tors include resi XXX > or to include only one specific definition in refinement > restr tors include resi XXX name var_1 > > In CCP4i you'll have to include this with the Developers Option to include an > external keyword-file. NOTE: Without doing anything, the torsion definitions > are still NOT used, which would explain the behaviour you observe. This is a > feature, not a bug .... > > I'am not sure what the situation is in the current version, maybe Garib > should answer this? > > Hope that helps, > Eckhard > > > > Huiying Li schrieb: >> I want to impose restraints during REFMAC refinement on the tortion angles >> that control the tilting of an OH group from a plane in a ligand bound to >> the protein. A few things that confused me: >> >> 1. In library cif file, should I just increase or decrease the >> tor.value_angle_esd if I want to loosen or tighten the restraits? >> >> 2. What is the meaning of the last column in torsion angle parameters: >> _chem_comp_tor.period, in cif file? In the PDB output file REFMAC also >> lists the RMS and WEIGHT for the torsion angles, period 1 through 4. >> >> 3. In REFMAC gui under Geometric parameters, there is only one user >> controlled weight for torsion. By changing the weight here, does it change >> the torsion weight for all 4 periods? >> >> Thanks in advance for the help. >> >> Huiying > > > -- Huiying Li, Ph. D Department of Molecular Biology and Biochemistry Natural Sciences I, Rm 2443 University of California at Irvine Irvine, CA 92697, USA Tel: 949-824-4322(or -1953); Fax: 949-824-3280 email: [log in to unmask]