Hi Carmela,
as Jacob suggests, the real space group may be P2 or P2(1). You need to prepare 3 MTZ files, each corresponding to a different unique b axis.
So just run XDS 3 times, each time with JOB=CORRECT and SPACE_GROUP_NUMBER=3, and afterwards XDSCONV to create a MTZ file (or pointless/aimless).
First time:
UNIT_CELL_CONSTANTS= 58 103 220 90 90 90
Second time:
UNIT_CELL_CONSTANTS= 103 220 58 90 90 90
Third time:
UNIT_CELL_CONSTANTS=220 58 103 90 90 90
Then, if you have a good model, do MR with each MTZ file, taking care that both P2 and P2(1) are tested. Or experimental phasing, but that requires good data.
HTH,
Kay
On Sun, 3 Dec 2017 18:29:57 +0100, Carmela Garcia <[log in to unmask]> wrote:
>Hi,
>
>The dimensions for a native are 58 103 220, with small differences for the derivatives.
>
>Best,
>
>Carmela.
>
>> On 3 Dec 2017, at 18:18, Sridhar Prasad <[log in to unmask]> wrote:
>>
>> Hello,
>> Can you please share the unit cell dimensions.
>>
>> Cheers,
>> Sridhar
>>
>> On Dec 3, 2017 9:13 AM, "Carmela Garcia" <[log in to unmask] <mailto:[log in to unmask]>> wrote:
>> Dear all,
>>
>> I know that some years ago a similar situation was discussed here, and I wonder if someone has new insights about these problems.
>>
>> My protein is a dimer in solution. I tried several derivatives for SAD, and all my datasets seem to have the same problem, including the native crystals. I processed the data with XDS and the space group determination was done with Pointless, being a P212121.
>>
>> Checking the quality of the data, I found several problematic results:
>>
>> - Translational NCS is detected. There is a peak at (0.50, 0.40, 0.50)
>> - The L test suggests twinning (L statistic = 0.41)
>> - The mean acentric moments I from input data have the following values:
>> <I^2>/<I>^2 : 4.396
>> <I^3>/<I>^3: 34.478
>> <I^4>/<I>^4: 361.084
>> All these values are way higher than the expected ones for non-twinned data.
>> - The twinning fraction from L-test is 0.22
>>
>> This would all suggest that my space group is wrong, and that I should proceed in a lower symmetry group, but I don’t know how should I continue. I know about cases where a P43212 or a P41212 were suggested but in fact the correct space group was P212121, but I would not know how to continue going down. Checking my images, I can see some streaky spots, and the crystals grow first as needles that eventually become plates and rarely crystals. All these would be a clear indicative of twinning, but I would not expect to have the same results with different derivatives. We thought about some kind of reticular twinning, and I wonder if there is a way to solve it.
>>
>> Any idea about how to proceed or to identify the problem would be welcome.
>>
>> Thanks,
>>
>> Carmela.
>>
>>
>>
>> Carmela Garcia-Doval
>> University of Zurich
>> Department of Biochemistry
>> Winterthurerstrasse 190 <https://maps.google.com/?q=Winterthurerstrasse+190&entry=gmail&source=g>
>> CH-8057 Zurich
>> Switzerland
>> E-mail: [log in to unmask] <mailto:[log in to unmask]>
>
>
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