HSA has a molecular mass of 66.5 kDa. When I did DLS measurements for pure HSA I was expecting to see large-sized particles. However, I ended up having 8-9 nm particles which I later found it does agree with literature value. My question is if there is a correlation between molecular mass of a protein and its particle size measured by DLS ?
You obviously prepared or filtered your samples well without problems. Yes, there is a direct link between molecular mass and size as you would expect.
Thanks, yes I did filter my samples well. So does the measured particle size (8 nm) makes sense with molecular mass of HSA ?
Yes, this is a correct value for hydrodynamic diameter (Dh) of HSA. Hydrodynamic radius Rh will be twice smaller (4 nm). Proteins are usually compact objects and you can assume that Mw ~(Rh)^3. I think Malven software has an incorporated calculator to predict the size of a protein from its molecular weight.
As Sergey has correctly indicated there's a calculator within the Malvern Zetasizer software that allows the calculation of size from molecular mass and vice versa plus prediction of required or minimum concentrations for optimal signal-to-noise. There is an assumption of shape - globular, random coils etc. Have a look at the Materials Talks and Malvern websites. For example:
http://www.materials-talks.com/blog/2017/03/07/can-i-use-dls-for-xyz/
http://www.materials-talks.com/blog/2017/03/07/can-i-use-dls-for-xyz/
http://www.materials-talks.com/blog/2016/12/27/what-is-a-virus/
Using aforesaid calculator and your stated 66.5 kDa gives an estimated hydrodynamic radius of 3.6 nm or a diameter of 7.2 nm (see attached) for a globular protein in line with your measurements. Obviously you can estimate the (small) content of any oligomers or aggregates in the sample.
The reason I did not indicate this in my first reply is that this question has been asked before on RG. For example: https://www.researchgate.net/post/How_do_I_relate_molecular_weight_of_protein_in_kilodalton_to_its_size_in_microns
Quoting Richard Pace's answer in the last RG link:
Using Equation 2.1 of Erickson's work on protein size, we can estimate the size of a globular protein via : V(nm3) = 1.212x10-3(nm3/Da) * MW(Da)
Erickson, H. P. (2009). Size and shape of protein molecules at the nanometer level determined by sedimentation, gel filtration, and electron microscopy. Biological procedures online, 11(1), 32
Hi Mustafa,
there is an empirical relationship between size and molecular mass for globular proteins, and it is close to MW~size^2.34 so almost volume. There is a calculator integrated into the Malvern software.
The size you found is slightly larger than the monomer, most likely there is an equilibrium of monomer and dimer in the sample. This should also manifest itself as a slightly larger polydispersity than monomer alone.
http://www.materials-talks.com/blog/2016/01/21/zetasizer-sensitivity-for-protein-dls/
http://www.materials-talks.com/blog/2014/09/16/faq-molecular-weight-estimate-from-dls/
http://www.materials-talks.com/blog/2015/03/09/how-to-get-the-latest-software-for-the-zetasizer-nano/
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