[phenixbb] NCS restraints

Pavel Afonine pafonine at lbl.gov
Thu Jun 30 21:55:45 PDT 2011

Hi Yuri,

> 1- I think its somewhat of a consensus that at higher res. it should 
> not be used to avoid missing out "real" detailed discrepancy. Is this 
> true?

yes and no. Relevant methods are in active development and in general 
things change quickly. To get some very superficial impression, see 
pages 56-59 here:

> 2- Should one try to use it in lower res data (3 A and worse)?

Definitely yes. In phenix.refine there are two types of NCS restraints, 
applied in Cartesian or torsion angles spaces (global/local). Torsion 
NCS supposed to be the best but the relevant code in phenix.refine is 
too fresh and requires more testing. You should try both to see which 
one works best for you.

> 3- Is the presence of NCS macromolecule specific, or crystal specific? 

It's rather packing.. Say, if more than one copy packs in the asymmetric 
unit then you have NCS, roughly speaking..

> In other words, if for the same enzyme one crystal goes to 3.1 and 
> another 1.5 A could one have significant NCS but not the other?

I'm not sure I understood this... May some one else did?


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