An ankyrin repeat chaperone targets toxic oligomers during amyloidogenesis

Updates on Aβ Processing by Hsp90, BRICHOS, and Newly Reported Distinctive Chaperones

Alzheimer's disease (AD) is an extremely devastating neurodegenerative disease, and there is no cure for it. AD is specified as the misfolding and aggregation of amyloid-β protein (Aβ) and abnormalities in hyperphosphorylated tau protein. Current approaches to treat Alzheimer's disease have had some success in slowing down the disease's progression. However, attempts to find a cure have been largely unsuccessful, most likely due to the complexity associated with AD pathogenesis. Hence, a shift in focus to better understand the molecular mechanism of Aβ processing and to consider alternative options such as chaperone proteins seems promising. Chaperone proteins act as molecular caretakers to facilitate cellular homeostasis under standard conditions. Chaperone proteins like heat shock proteins (Hsps) serve a pivotal role in correctly folding amyloid peptides, inhibiting mitochondrial dysfunction, and peptide aggregation. For instance, Hsp90 plays a significant role in maintaining cellular homeostasis through its protein folding mechanisms. In this review, we analyze the most recent studies from 2020 to 2023 and provide updates on Aβ regulation by Hsp90, BRICHOS domain chaperone, and distinctive newly reported chaperones.

An ankyrin repeat chaperone targets toxic oligomers during amyloidogenesis

Numerous age-linked diseases are rooted in protein misfolding; this has motivated the development of small molecules and therapeutic antibodies that target the aggregation of disease-linked proteins. Here we explore another approach: molecular chaperones with engineerable protein scaffolds such as the ankyrin repeat domain (ARD). We tested the ability of cpSRP43, a small, robust, ATP- and cofactor-independent plant chaperone built from an ARD, to antagonize disease-linked protein aggregation. cpSRP43 delays the aggregation of multiple proteins including the amyloid beta peptide (Aβ) associated with Alzheimer's disease and α-synuclein associated with Parkinson's disease. Kinetic modeling and biochemical analyses show that cpSRP43 targets early oligomers during Aβ aggregation, preventing their transition to a self-propagating nucleus on the fibril surface. Accordingly, cpSRP43 rescued neuronal cells from the toxicity of extracellular Aβ42 aggregates. The substrate-binding domain of cpSRP43, composed primarily of the ARD, is necessary and sufficient to prevent Aβ42 aggregation and protect cells against Aβ42 toxicity. This work provides an example in which an ARD chaperone non-native to mammalian cells harbors anti-amyloidal activity, which may be exploited for bioengineering.