Did you check for twinning? The most radical approach is to reprocess in P1 and see what R-values you get
On Mon, 2011-10-17 at 15:09 -0200, Napoleão Valadares wrote: > Hi there! > I got crystals from some synthetic peptides I bought, they are 30 > residues long and are supposed to form a coiled coil. I collected > various data sets (home source, Brookhaven and Diamond), including some > at the resolution of 1.65 A, for which the space group appears to be > C222 or C2221. The unit cell is small, 22.67, 88.06, 26.13, and the > Matheus Coefficient indicates that's there's only one helix in the > asymmetric unit and a 25% solvent content. > > I have tried A LOT of Molecular Replacement using Phaser and Phenix > AutoMR. I'm using a 80% identity coiled coil helix as search model. The > programs give me solutions with "reasonable" maps, but it is never > possible to refine to achieve Rvalues below 0.40. Additionally, maps > from different solutions look reasonable, so I'm thinking these are all > bias. > > I have 5 other synthetic 30 residues peptides (that crystallize in > different space groups and diffract to lower resolutions), including a > SelenoMethionine (SM) derivative (but it does not have enough anomalous > signal, ASU is too big, it is possible that the SM are disordered). I'm > stuck on this since March. > > Regarding the search model, I already tried trimming some or all > side chains and removing 2, 3 or 5 residues on each/both sides. I also > tried other search models. Maybe some "magic" combination of parameters > on Phaser or other programs can help me. > > What is your advice regarding how to proceed with MR? Is there some > program, procedure, parameter, pray or human sacrifice that could help me? > Thank you. > Regards, > Napo -- Edwin Pozharski, PhD, Assistant Professor University of Maryland, Baltimore ---------------------------------------------- When the Way is forgotten duty and justice appear; Then knowledge and wisdom are born along with hypocrisy. When harmonious relationships dissolve then respect and devotion arise; When a nation falls to chaos then loyalty and patriotism are born. ------------------------------ / Lao Tse /
