Peak (21.44, 0, 180) has symmetry-related peak (111.44 0 180).
These two peaks are identical because NCS peak (21.44, 0, 180) is
pependicular to CS peak (90 90 180)
Two perpendicular 2-fold peaks (NCS and CS) generate
additional 2-fold axis (111.44 0 180). It's called "Klug" peak.
Regards
Alexei
On 23 Apr 2008, at 13:39, Derek Logan wrote:
> Hi everyone,
>
> Can anyone help me with interpretation of a self rotation function
> and native Patterson from a dataset with pseudosymmetry? I've
> always been a bit poor on spherical polars. The space group is P21
> with beta = 92.2°. The kappa=180° section of the SRF, calculated
> using Molrep, is at
>
> http://mole.mbfys.lu.se/~derek/selfRF_180.png
>
> and contains two big peaks around 7 sigma. I'm having trouble
> identifying these in the list of peaks from Molrep:
>
> theta phi chi alpha beta gamma
> Isym_i Isym_j
> Sol_RF 1 0.00 0.00 0.00 0.00 0.00 0.00 1 1
> Sol_RF 1 90.00 -90.00 180.00 0.00 180.00 0.00 1 2
> Sol_RF 1 90.00 90.00 180.00 0.00 180.00 0.00 2 1
> Sol_RF 1 0.00 0.00 0.00 0.00 0.00 0.00 2 2
> Sol_RF 2 158.56 180.00 180.00 0.00 42.89 -180.00 1 1
> Sol_RF 2 111.44 0.00 180.00 -180.00 137.11 0.00 1 2
> Sol_RF 2 111.44 0.00 180.00 180.00 137.11 0.00 2 1
> Sol_RF 2 21.44 0.00 180.00 180.00 -42.89 0.00 2 2
> Sol_RF 3 165.65 0.00 180.00 -180.00 28.70 0.00 1 1
> Sol_RF 3 104.35 -180.00 180.00 0.00 151.30 180.00 1 2
> Sol_RF 3 104.35 180.00 180.00 0.00 151.30 -180.00 2 1
> Sol_RF 3 14.35 -180.00 180.00 0.00 -28.70 180.00 2 2
>
> It seems to me to be two copies of peak 2. I believe theta starts
> in the middle, perpendicular to the page and phi starts on the x
> axis, thus the peak just below the centre would be (21.44, 0, 180).
> I presume that the second peak is the symmetry-related (158.56,
> 180, 0)? However where is (111.44 0 180)? I would expect to see
> this near the bottom of the plot, but it's not there. I'm sure I'm
> missing something fundamental about the symmetry of the SRF
> projection, but unfortunately I don't have a supervisor to bug
> about this (I *am* the supervisor...)
>
> In the native Patterson
>
> http://mole.mbfys.lu.se/~derek/nativePatterson.png
>
> there are two peaks of almost equal height. How can this be
> reconciled with having only one strong peak in the SRF? There are
> most likely two dimers in the asymmetric unit, but there may only
> be one, with very high resulting solvent content. What's more the
> molecules are leucine-rich repeat proteins and have weak internal
> symmetry. I believe this was an issue with the ribonuclease
> inhibitor, but looking briefly at the crystallisation article and
> structure article I wasn't able to find a rationalisation of this
> problem. The 2-fold is perpendicular to b*. How could this cause
> the two peaks?
>
> Thanks
> Derek
>
>
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