[ccp4bb] Possible C2 Twinning

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

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From: H Park haj {- dot -} park {- at -} GMAIL {- dot -} COM
Date: 2009-06-16

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Subject: Re: Possible C2 Twinning
From: Ian Tickle I {- dot -} Tickle {- at -} ASTEX-THERAPEUTICS {- dot -} COM
Date: 2009-06-16

Subject: Possible C2 Twinning
From: Jeffrey D Brodin jbrodin {- at -} UCSD {- dot -} EDU
Date: 2009-06-16

Dear ccp4bb,

I've recently run into a problem refining a crystal structure that I indexed and performed a molecular replacement on as C2. The unit cell dimensions are a=96, b=95.8, c=58.1 and beta=127; Rmrg=.195. The data go down to a resolution of 2.8 angstroms. The data also index in I222, but scaling statistics are worse (Rmrg = .598) and Molrep does not find an acceptable solution. Using the C2 space group Molrep finds a solution with the expected 4 monomers (protein size is ~12.5kd) in the asymmetric unit, but I have only been able to refine it to an R/Rfree of 33/37. The asymmetric unit consists of two dimers, and performing a two-fold rotation around an axis perpendicular to the helices of the dimers generates the tetramer that we would expect from other experimental data. Also, the backbone density for two of the monomers is much worse than normal. Truncate shows possible twinning in that the 4th centric moment of E has an observed value of 2, which is what would be expected for a perfect twin (actual expected value is 3) and the first and third centric moments are .87 and 1.45 respectively, with expected values of .8 and 1.6 and .89 and 1.33 for perfect twins. I am new to resolving twinning issues and was wondering if anyone has any ideas as to whether I may have the space group wrong or if there is a twinning operator that I could use to resolve this issue. Thanks in advance for your help,

Jeff

CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: For Sale - Rigaku MicroMax-007 HFM X-ray Generator
From: H Park haj {- dot -} park {- at -} GMAIL {- dot -} COM
Date: 2009-06-16

Next message:
Subject: Re: Possible C2 Twinning
From: Ian Tickle I {- dot -} Tickle {- at -} ASTEX-THERAPEUTICS {- dot -} COM
Date: 2009-06-16