Hi
A few months ago, I read a paper proposing a new approach for spectral
density mapping : fast spectral density mapping.
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Ropars et al. (2007) JBNMR, 37:159-177.
Unraveling protein dynamics through fast spectral density mapping
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This approach yields n + 2 spectral densities when measuring n + 2
relaxation parameters, while the standard reduced spectral density
mapping needs 3n measurements to yield 2n + 1 spectral densities.
The new approach assumes that the high frequency approximation is valid,
that is a single J(wH) is equivalent to different J(wH), for example
J(wH) = J(500 MHz) = J(600 MHz) = J(750 MHz) = J(800 MHz)...
The two approaches need 3 relaxation rates to yield J(0), J(wN) and
J(wH). However, if one wants :
J(0), J(wN1), J(wH1), J(wN2), J(wH2)
fSDM : 4 measurements needed (field 1 : R1, R2, NOE ; field 2 : R1)
rSDM : 6 measurements needed (field 1 : R1, R2, NOE ; field 2 : R1,
R2, NOE)
J(0), J(wN1), J(wH1), J(wN2), J(wH2), J(wN3), J(wH3)
fSDM : 5 measurements needed (field 1 : R1, R2, NOE ; field 2 : R1 ;
field 3 : R1)
rSDM : 9 measurements needed (field 1 : R1, R2, NOE ; field 2 : R1,
R2, NOE ; field 3 : R1, R2, NOE)
J(0), J(wN1), J(wH1), J(wN2), J(wH2), J(wN3), J(wH3), J(wN4), J(wH4)
fSDM : 6 measurements needed (field 1 : R1, R2, NOE ; field 2 : R1 ;
field 3 : R1 ; field 4 : R1)
rSDM : 12 measurements needed (field 1 : R1, R2, NOE ; field 2 : R1,
R2, NOE ; field 3 : R1, R2, NOE ; field 4 : R1, R2, NOE)
Thus, only R1 needs to be acquired at different fields with R2 and NOE
only needed at one field with preference for a R2 measured at the lowest
field to minimize possible exchange contributions.
As as can be seen, the requirements for data acquisition are much
smaller and this approach could eventually be used by some people.
Thus, should this approach be integrated into relax ?
If yes, how should it be integrated ? Should all the different
approaches to reduced spectral density mapping (the one actually
available, the multiple field approach, the fSDM, and any other) be
merged together and a flag specified by the user to choose between the
different methods ?
Cheers
Sébastien :)
--
Sebastien Morin
Etudiant au PhD en biochimie
Laboratoire de resonance magnetique nucleaire
Dr Stephane Gagne
CREFSIP (Universite Laval, Quebec, CANADA)
1-418-656-2131 #4530
Fast spectral density mapping