[3dem] Resolution estimate: FSC vs PDB modeling
Penczek, Pawel A
Pawel.A.Penczek at uth.tmc.edu
Wed Mar 12 15:07:36 PDT 2014
Hi,
the point I wanted to make may or may not be relevant to the current current discussion, but as
it is sometimes confused I would like to clarify it again.
The FSC estimate (comparison of two NOISY half-maps or two noisy maps in general)
is not numerically equivalent to what I call cross-resolution (FCR), which is a comparison of
a noisy map with a NOISE-FREE map. This would be for example a comparison of an EM map with
a PDB-derived model, the latter for the sake of simplicity considered noise-free.
It can be shown that
FCR = sqrt(FSC)
In simple words, if one estimated EM resolution from half-maps using FSC and say 0.5 cut-off,
the cross-resolution FCR of the same map with a X-ray derived model should be 0.71 at the same
frequency to be equivalent. If FCR is 0.5, the cross-resolution would point at much poorer agreement.
Again, if one uses 0.5 as a cut-off for FSC, one should use 0.71 for FCR; if 0.147265 for FSC, 0.383 for FCR,
and so on…
For FSC there is also factor of two hanging there.
For more details please see
Penczek, P.A.: Resolution measures in molecular electron microscopy. Methods Enzymol 482, 73-100, 2010.
Regards,
-
Pawel Penczek
pawel.a.penczek at uth.tmc.edu<mailto:pawel.a.penczek at uth.tmc.edu>
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