Methods for measuring protein aggregation

Misfolded proteins can aggregate into complexes of varying size and structure, generally with a concomitant loss of protein function. These aggregates frequently impede expression, purification, analysis, and storage of wild-type and mutant proteins to be used for research or as pharmaceuticals. Human health can be severely affected by protein misfolding and aggregation resulting from genetic mutations, medical treatment, or prion diseases (tauopathies). Analysis of protein aggregation is therefore an important facet of many areas of protein chemistry and related fields. Three categories of aggregation experiments are reviewed. First, characteristic data anomalies from common protein methods indicate the presence of aggregates. Second, once aggregation has been identified, several techniques are available to screen for solvent conditions that promote protein solubility. Finally, methods that characterize aggregate structure allow investigation of the process of protein coagulation. These methods vary in the required amount and purity of sample, the cost and difficulty of implementation, the type of aggregate detected, and the ability to be applied for quantification and kinetics. Approaches to improve protein solubility through the addition of co-solvents or the alteration of over-expression strategies are also reviewed.