SHELXD does not use the solvent content. However since you know how many
seleniums it found and presumably know how many methionines are in the
sequence, you can use that to estimate the number of molecules is the
asymmetric unit. Note that an N-terminal selenomethionine is often
disordered and so should not be counted, and that there is a twofold
axis in P43212 that could be used to form the dimer.
I would start by throwing the P43212 sites into the autotracing version
of SHELXE (with and without -i, just in case it is P41212) and seeing if
it traces. If one of these two space groups traces appreciably better
than the other, then you have solved it. At 2.9A the traces will not be
complete but should be good enough for this purpose. If as seems likely
you have NCS, you can improve them by using the -n switch.
George
On 12/06/2011 09:16 PM, Tiruttani Subhramanyam, Udaya Kumar wrote:
hi
I have a 2.9 ang selenomet MAD data set integrated in four space groups P4,
P422, P222 and C222
i had to integrate in all the four space groups as I was stuck in refining the
model in P422
by using shelxD I found solution in P43, P43212 and p212121 but not in C222
the CC all/weak for them are as follows
P43212 52.51 / 34.57
P43 43.12 / 25.73
P212121 48.63 / 31.74
i donot know how many molecules are there in the asymmetric unit but
dimerization of the protein is know from which i can say it could be even
number.
but matthews coef shows high probability for heptamer. so i used that solvent
content in all the above runs.
another observation is that at 3.3 ang resolution the anomalous CC % value are
39.2, 35.3, 32.5 and 28.4 for p43212, p43, c2221 and p212121 respectively.
in all cases P422 looks better in terms of SHELXC stats. i am afraid that there
is twinning involved.
could anyone suggest me whether its possible to conclude the right space group
among them.
With regards
uday
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