If for example your presumed coil is differently bent than your search probe, overall rmsd is high and MR will likely fail. But maybe ARCIMBOLDO with helix fragments might do at 1.65A? George or Isabel will have a better answer.
Good luck, BR PS: And may San Matheus de las Coefficientes listen to your prayers... :-) -----Original Message----- From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Napoleão Valadares Sent: Monday, October 17, 2011 10:09 AM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] MR - small coiled coil, 1.65A = 1.000 solutions, all of them wrong 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
