[RASMB] problem with fitting

[Fasolini, Marina [Nervianoms]]

Dear AUC users,
I have a problem in the fitting of some data and I would like to have your opinion.
 
I want to control the sedimentation of a protein in order to define the state of oligomerization. It is published as forming an  hexameric homo oligomer. From the crystal structure, it is a wheel like structure of 160 angstrom  in diameter, with a central role of 15 angstrom in diameter. The thickness is 20-40 angstrom. How can I expect it to sediment? How can I improve my parameters or model in order to improve the fitting?
 
The protein is 50KDa  but in gel filtration it cames out as  hexamer (300 KDa). In my sedimentation experiment I see one peak of  6.23S which corresponds to 140KDa. Fitting of the sedimentation data was done with SedFit. Do you think I can say that it is a trimer? I would expect it as an hexamer.
 
I hope someone can help me. 
 
the conditions are : 
buffer 20mM Tris pH7, 150mM NaCl, 1mM DTT, 5%gly 
Vbar 0.7397 
Viscosity 1.02530 
Density 0.01183 
 
Thanks a lot
Marina 
 
 
 
MARINA FASOLINI
Structural Chemistry 
Nerviano  <http://www.nervianoms.com/> Medical Sciences
Viale Pasteur 10
20014 Nerviano - Milano
marina.fasolini at nervianoms.com
Tel. +390331581462
Fax. +390331581360
 
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