[ccp4bb]: DLS: discrete dimer vs random assemlby

[diane h peapus <dp72@cornell.edu>]

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Hi Everone:

Sorry....
This is not CCP4-related, but there don't seem to be any
other active mailing lists or bbs's on other xtallographic
topics.  ;-(

I'm running dynamic light scattering (DynaPro99) and am
wondering how to interpret what I'm looking at.  If any
experts out there, I'd appreciate any input.

scenerio:
I have a protein where the active form and a previous 
xtal form both are homo-dimers (45kDa monomer).  Previous
xtal conditions were not screened for DLS.  I observe
the protein as a sharp monomer DLS peak in the storage 
buffer and as a BROAD DLS peak centered around 500kDa 
in the previously successful xtallization conditions.  
(This is the same protein that gave xtals, but 2 months 
later.)

I can decrease the precipitant concentration to a point 
where I find a slightly-less-broad DLS peak centered 
around 100kDa... which _could_ correspond to the dimer... 
or to the average MW of a random distribution of monmers
and small-ish agregates.

My thinking is that it's the small-ish aggregate option.
My thinking is that if it were the active dimer form, 
the distribution would be just as sharp as the monomer
distribution in storage buffer.

I'm wondering if anyone has any rule of thumb about how 
sharp a peak needs to be to call the solution homogenious?  

Thanks
diane


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