[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[ccp4bb]: anisotropic crystals



***  For details on how to be removed from this list visit the  ***
***    CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html    ***

Hi All,

We have some crystals, P41 or P43, 2.5 A resolution. The stats from
scalepack look fine, but in truncate things look worse.

The Wilson B is high - 63 A^2

The observed accumulative intensity distributions are significantly
_higher_ than the theoretical ones (ie the opposite of what is observed
in twinned cases).

         Z   N(Z)Atheor  N(Z)Acen  N(Z)Ctheor  N(Z)Cen    
 
        0.0       0.0       0.0       0.0       0.0
        0.1       9.5      14.9      24.8      34.6
        0.2      18.1      23.4      34.5      45.3
        0.3      25.9      31.6      41.6      54.2
        0.4      33.0      38.9      47.3      62.0
        0.5      39.3      45.5      52.1      67.6
        0.6      45.1      51.1      56.1      71.7
        0.7      50.3      56.2      59.7      75.1
        0.8      55.1      60.4      62.9      79.0
        0.9      59.3      64.3      65.7      81.3
        1.0      63.2      67.6      68.3      83.3


Truncate also warns of serious anisotropy with F along c being 1.7 
times F along a or b:

Average F (d1 d2 d3) + overall average:    98.49    99.49   172.07      
117.47

We get a strong, sensible molecular replacement solution with amore and
cns in P41, but refinement fails to lower the R-free.

I would be surprised if the space group assignment is wrong - the unit
cell dimensions are clearly tetragonal and the l = 4n condition is very
clear.

Has anyone else had experience with such data? Is the anisotropy
responsible for the strange accumulative I distribution? If the
anisotropy corrections in refmac and cns can not suitably model the
observed anisotropy, is there any other way to tackle this?

Cheers,
Charlie

-- 
| Dr Charles S. Bond      | MSI/WTB Complex | Tel: +44-1382-345744  |
|                         | Dow Street      | Fax: +44-1382-345764  |
| Dept of Biochemistry    | Dundee DD1 5EH  |                       |
| University of Dundee    | Scotland        | C.S.Bond@dundee.ac.uk |