Mechanisms of fibrillar and colloidal aggregation

The physics of colloids has developed many theoretical and experimental tools to study the processes of aggregation and formation of supramolecular structures. The same approach has been gradually extended to the field of protein aggregation. Proteins or peptides may assemble in a variety of morphologies (e.g. crystals, polymers, amorphous gels), which have a functional or pathological role in the physiology of cells and living organisms. In particular, the formation of elongated linear proteinaceous structures, called amyloid fibrils. is of high relevance in many systemic and neurodegenerative diseases. The affinities between colloidal aggregation and protein fibrillation are the scope of the present work. Here, we briefly review the theory of colloidal coagulation in those aspects that may be relevant for the study of protein fibrillation, and recall a few experimental work, in which such a connection has been successfully used to gain an insight into the mechanisms of fibril morphogenesis. In particular, an accurate description is given for the interesting case of fibril elongation by addition of single monomers.