Classification of Protein Aggregates1

Comparison of protein aggregates/self-associated species between laboratories and across disciplines is complicated by the imprecise language presently used to describe them. In this commentary, we propose a standardized nomenclature and classification scheme that can be applied to describe all protein aggregates. Five categories are described under which a given aggregate may be independently classified: size, reversibility/dissociation, conformation, covalent modification, and morphology. Possible subclassifications within each category, several examples of applications of the nomenclature, and difficulties in making appropriate assignments will be discussed.