The role of the N-terminal p.R56Q mutation in modulating oligomerization and chaperone activity of human αB-crystallin in relation to cardiomyopathy

Abstract

αB-crystallin (αB-Cry), a critical small heat shock protein, is crucial for cellular proteostasis, especially in the heart and lens. αB-Cry mutations can disrupt its chaperone activity, leading to pathological conditions such as myopathy, cardiomyopathy, and cataracts. The p.R56Q mutation in the N-terminal domain, a region that participates in oligomerization as well as interactions with key proteins such as desmin and αA-Cry, has been associated with cardiomyopathy. However, its specific pathogenic mechanism is not well understood. This study aimed to elucidate the structural and functional consequences of the p.R56Q mutation. Recombinant p.R56Q αB-Cry was purified by chromatographic methods. Moreover, spectroscopic, microscopic, and computational techniques were employed to assess the influence of the mutation on protein function, structure, and stability. Our findings indicated that the p.R56Q mutation leads to significant alterations in human αB-Cry secondary to quaternary structures. The mutant protein was less stable and more prone to forming amyloid-like aggregates. The p.R56Q αB-Cry also formed larger oligomers and exhibited enhanced chaperone activity compared to its wild-type (Wt) protein counterpart. Interestingly, it had a greater affinity for binding to desmin and αA-Cry. While increased chaperone function might be expected to have protective effects, it could interfere paradoxically with critical cellular processes, such as apoptosis, and thus enhance disease pathogenesis. This research provides new insights into the molecular mechanisms underlying αB-Cry-associated cardiomyopathy by highlighting how the p.R56Q mutation alters structural dynamics and chaperone activity.