Re: [ccp4bb]: protein structures and hydrogens

["Eleanor J. Dodson" <ccp4@ysbl.york.ac.uk>]

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Joerg Mueller wrote:
> 
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> Dear all,
> 
> The question is not really related to this topic, but a probably a
> bit....
> When should one put Hydrogen atoms in an atomic resolution structure?
> Are there clear criteria like the drop in free R-value or resolution
> limit etc.?
> 
> Regards and thanks for help
> Joerg
> 


 Why dont people always include hydrogens when their models are good?
They are still there, even in crystals which only diffract to lower
resolutions. Positioning them at "riding" positions and including them
in the structure factor calculation has always reduced R values for me.
Of course if you still have a pretty imperfect model it will not
generate correct H positions, and it isnt worth the effort of placing
them, but towards the end they improve things. THe best documented
results are for main chain O where B factors and bond lengths can be
shown to improve after addition of hydrogen, but prob. the same
improvement is present everywhere.

 It takes a lot of very high resolution data to be able to refine them
though!

 Eleanor