Gly phi constraints

[John Kuszewski]

In article <48d4q1$36b at news.ox.ac.uk>, Kristy Downing <kristy at bioch.ox.ac.uk> writes:
|> Dear All,
|> 
|> I have extracted coupling constants corresponding to Gly HA1-HN and HA2-HN from
|> a HNHA experiment, and I would now like to use this information to derive
|> backbone phi constraints.  I have two questions:
|> 
|> (i) How do the couplings relate to the phi angle?  For example, if one HA-HN
|> coupling constant is 4.0 Hz and the other is 7.4 Hz, what equation do I use to
|> derive phi?  (If anyone knows of a reference, I would be very grateful!)

I just talked to Andy Wang, one of Ad Bax's postdocs, about this.  
The Karplus curve that Vuister and Bax published (as well as a re-worked
version that Andy and Ad have in-press) does not work well for gly.

I wouldn't try to include phi restraints from gly 3J HnHa couplings.

|> 
|> (ii) Are glycine phi constraints encoded the same way in X-PLOR as other
|> backbone torsion angle constraints, i.e., using the atoms of C(i-1), N, CA, and
|> C?

Yes, although better ways of dealing with this information,
such as my direct refinement techniques, have been developed too.


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John Kuszewski                     ||  |/  /|  ||      
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