[ccp4bb] MR - small coiled coil, 1.65A = 1.000 solutions, all of them wrong

[Napoleão Valadares]

    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