[RASMB] Frict ratios and sedfit

[Samantha Jones (PRION)]

Hello
I recently analyzed some data using c(S) distribution model on Sedfit.
The distribution showed a few peaks, with the main peak being at 4S. I
floated the frictional ratio and came back with approx 1.5. I then
converted this to a c(M) distribution with the main peak now showing
approx 65,000 Daltons. Knowing our monomer weight as 16,400 Daltons I
concluded this was a tetramer.
At the same time the same protein sample was analyzed using synchrotron
X ray scattering. Their results concluded an octomer, a two ring
structure.
With this knowledge I went back to the data and reanalyzed using Sedfit,
c(s) and c(M) again. Using the calculator function on Sedfit I
calculated that for 4S with a frictional ratio 1.5 this would be roughly
the tetramer weight, however, a frictional ratio of 2.4 for 4s gives a
molecular weight equal to the octomer. When I entered this into the
parameters of the c(M) model the rsmd values show the f/f0 of 2.4 gives
a better fit, 0.07 to 0.119 for f/f0 of 1.5.
My question is how I could have got this answer without the knowledge of
the scattering data? Is the use of the calculator function to fit data
recommended? Especially in a sample with three peaks?
 
Many thanks
 
Samantha 
 
Samantha Jones
MRC Prion Unit
Institute of Neurology
Queen Square
London
WC1N 3BG 
 
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