[phenixbb] Anisotropic B-factors with Trucated Data

Pavel Afonine pafonine at lbl.gov
Sat Aug 1 09:23:19 PDT 2015

Dear John,

> 1.7 Angstrom resolution seems to me awfully low for thinking about anisotropic protein model refinement! Ie in terms of number of diffraction data to model parameters.

in refinement we use restraints that contribution is added with variable 

Ttotal = Tdata + w * Trestraints .

One can think of Trestraints being "observations" added to the actual 
data in different amounts depending on choice of the weight w.

This is exactly why we can still refine individual coordinates or 
isotropic B-factors at "macromolecular" resolutions like 2-6A or so. If 
we think of this in terms of data/parameters ratio counted as 
Nreflections vs Natoms*(4xyz+1B) (that is without restraints) that would 
be impossible but restraints do the trick.

Likewise, we can still refine anisotropic B-factors at resolutions 
beyond 1-1.2A. I agree 1.7A is a bit low(ish) but in favorable cases 
(data is very good and comes from a crystal that can diffract to a 
higher resolution) might be worth a try.

All the best,

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