I loaded Quick Start Bovine Serum Albumin Standard as my negative control in my Native PAGE run. I was able to see three oligomeric states (i.e. monomer, dimer and trimer) in my BSA lane. I was planning to use the BSA lane as a reference to determine the size of the protein I'm working with. Both BSA and the protein I'm working with are globular in structure. What I'm not sure of is if the BSA standard is in native condition or exist in its 3D structure when stored as stock. I've been looking for a product sheet with the necessary info but I can't find one.
I'm pretty sure that the BSA is mostly in its native state. It is held together by a lot of disulfide binds, so it is pretty stable. The presence of oligomers, especially dimers, is normal for BSA.
Thank you for the response Mr. Adam B Shapiro! I do also believe that it is native form since if it's denatured form, I think it would be impossible for BSA to form the observed oligomers.
The thought that it might be denatured came from the fact that the BSA standard I used is mainly used for protein quantification (Bradford assay). We wondered if the BSA standards used are in their 3D state since we assume in protein quantitation it is best if the denatured to account for all the possible amino acids that would react with Bradford reagent.
As Adam Shapiro stated, commercial BSA is in native state, because we use it as standard sometimes in SAXS (small angle X-ray scattering) experiments. It is well described here: https://www.sasbdb.org/data/SASDA32/
Thank you for the reference Mr. Lorenzo Briganti ! The link you attached is helpful.
I can assume safely that whether the BSA produced is for quantification or for other stated purposes, the protein is in its native state.
I'm just confused here: " In solution is present as a monomer-dimer equilibrium, therefore the molecular weight of the standard BSA is not the one of the monomer (68 kDa) but is slightly bigger (72 kDa)." Is the 72kDa weight is the one therefore observed when the protein is run in Native PAGE? I assumed that the size of the BSA monomer I see is 68 kDa since I planned to use it as a reference size.
You're welcome, Mr. Jareno!
I'm not a specialist in native PAGE, but the few times I used, I could notice more than 1 band for different oligomeric forms. I would say that with BSA you would probably see a strong monomeric band (~68 kDa), and perhaps a very weak dimeric band. In SAXS you see the average molecular weight of the molecules in solution, so the contribution of dimeric scattering makes the apparent molecular weight increase.
Commerical BSA does indeed contain higher oligomers under non-denaturing conditions. For this reason I have actually discouraged its use as a SAXS standard. This can routinely be seen in size-exclusion chromatography coupled SAXS measurements. The main peak is monomer, but the small secondary peak fits the crystallographic dimer as can be seen here: https://www.sasbdb.org/data/SASDFR8/