Co-chaperoning by amyloid-forming proteins: cystatins vs. crystallins.

Cystatins and crystallins are both neuroprotective proteins. Except for their function as cysteine cathepsins inhibitors, cystatins are Aβ binding proteins and presumably protect neurons from intracellular Aβ and extracellular Aβ plaques. Pathological mutations of cystatin C cause amyloid angiopathy. Crystallins, known as small heat shock proteins, bind not only Aβ peptide but also other crystallins in the eye lens and prevent their aggregation. Mutations in crystallins cause cataracts and myopathies. Cross-interactions between amyloidogenic proteins, intrinsically disordered and folded proteins, can also occur. I term the nonspecific binding between amyloidogenic proteins and peptides "co-chaperoning." A wide range of other Aβ binding proteins exist, such as catalase, lysozyme, β-lactoglobulin and some other abundant proteins found in plasma.