CSA & bond length -- September 28, 2006 - 20:49

Hi

I am new to relax and have a quite general question about the value used
for the CSA while studying proteins' 15N-1H vectors with model-free
approach.

In the litterature, we mainly find two values for the CSA (-160 and -172
ppm).

There is, if I understand well, a link between the bond length and the
CSA, but everyone seems to agree about using the same value of 1.02 A
which should give rise to a mean S2 of 0.85 for secondary structure when
combined to a CSA of -172 ppm.

In the relax sample scripts (as well as in the Model-free manual), a
value of -160 ppm is used for CSA.

What is the best value to use and, most importantly, why ?

Also, what about the CSA variability from one vector to another (JACS,
128 (24), 7855 -7870, 2006) ?

Thanks !


Sébastien

-- 

         ______________________________________    
     _______________________________________________
    |                                               |
   || Sebastien Morin                               ||
  ||| Etudiant au doctorat en biochimie             |||
 |||| Laboratoire de resonance magnetique nucleaire ||||
||||| Dr Stephane Gagne                             |||||
 |||| CREFSIP (Universite Laval)                    ||||
  ||| 1-418-656-2131 poste 4530                     |||
   || sebastien.morin.1@xxxxxxxxx                   ||
    |_______________________________________________|
         ______________________________________