Native Oligomeric State

Just what is a 'native oligomeric state'? The answer may surprise you since 'native' is a relative term. Most biological oligomers consist of proteins in a dynamic equilibrium between monomers and specific oligomers (e.g., dimers or tetramers). The ratio of oligomers to monomers depends on the concentration as well as buffer pH and ionic strength, and therefore changes with analysis conditions. True identification of a native oligomer must be performed wholly in solution since the solution conditions dictate the degree of oligomerization, and even the final oligomeric number.

Multi-angle light scattering (MALS) is one of the premier methods for identifying native oligomers and determining their stoichiometry. An initial diagnosis of oligomerization is often provided by SEC-MALS which might indicate that a protein's molar mass differs significantly from monomer sequence weight, or the mass may vary over the eluting peak, decreasing with decreasing concentration on both sides of the apex. Verification may be obtained by a few additional SEC-MALS measurements consisting of different starting concentrations.

In order to obtain a rigorous analysis of oligomeric state and the equilibrium dissociation constant Kd, composition-gradient multi-angle light scattering (CG-MALS) measures self-association as a series of stop-flow injections into a MALS detector. This procedure allows for complete equilibration as well as full analysis of oligomeric stoichiometry even if more than one oligomers are present.

Dynamic light scattering (DLS), while not as quantitative as MALS, is a rapid and productive means for estimating oligomerization properties through the concentration dependence of the average molecular size.