Myopathy-associated G154S mutation causes important changes in the conformational stability, amyloidogenic properties, and chaperone-like activity of human αB-crystallin

Unraveling the impact of the p.R107L mutation on the structure and function of human αB-Crystallin: Implications for cataract formation

To date, several pathogenic mutations have been identified in the primary structure of human α-Crystallin, frequently involving the substitution of arginine with a different amino acid. These mutations can lead to the incidence of cataracts and myopathy. Recently, an important cataract-associated mutation has been reported in the functional α-Crystallin domain (ACD) of human αB-Crystallin protein, where arginine 107 (R107) is replaced by a leucine. In this study, we investigated the structure, chaperone function, stability, oligomerization, and amyloidogenic properties of the p.R107L human αB-Crystallin using a number of different techniques. Our results suggest that the p.R107L mutation can cause significant changes in the secondary, tertiary, and quaternary structures of αB-Crystallin. This cataractogenic mutation led to the formation of protein oligomers with larger sizes than the wild-type protein and reduced the chemical and thermal stability of the mutant chaperone. Both fluorescence and microscopic assessments indicated that this mutation significantly altered the amyloidogenic properties of human αB-Crystallin. Furthermore, the mutant protein indicated an attenuated in vitro chaperone activity. The molecular dynamics (MD) simulation confirmed the experimental results and indicated that p.R107L mutation could alter the proper conformation of human αB-Crystallin dimers. In summary, our results indicated that the p.R107L mutation could promote the formation of larger oligomers, diminish the stability and chaperone activity of human αB-Crystallin, and these changes, in turn, can play a crucial role in the development of cataract disorder.

Understanding the structural and functional changes and biochemical pathomechanism of the cardiomyopathy-associated p.R123W mutation in human αB-crystallin

αB-crystallin, a member of the small heat shock protein (sHSP) family, is expressed in diverse tissues, including the eyes, brain, muscles, and heart. This protein plays a crucial role in maintaining eye lens transparency and exhibits holdase chaperone and anti-apoptotic activities. Therefore, structural and functional changes caused by genetic mutations in this protein may contribute to the development of disorders like cataract and cardiomyopathy. Recently, the substitution of arginine 123 with tryptophan (p.R123W mutation) in human αB-crystallin has been reported to trigger cardiomyopathy. In this study, human αB-crystallin was expressed in Escherichia coli (E. coli), and the missense mutation p.R123W was created using site-directed mutagenesis. Following purification via anion exchange chromatography, the structural and functional properties of both proteins were investigated and compared using a wide range of spectroscopic and microscopic methods. The p.R123W mutation induced significant alterations in the secondary, tertiary, and quaternary structures of human αB-crystallin. This pathogenic mutation resulted in an increased β-sheet structure and formation of protein oligomers with larger sizes compared to the wild-type protein. The mutant protein also exhibited reduced chaperone activity and lower thermal stability. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) demonstrated that the p.R123W mutant protein is more prone to forming amyloid aggregates. The structural and functional changes observed in the p.R123W mutant protein, along with its increased propensity for aggregation, could impact its proper functional interaction with the target proteins in the cardiac muscle, such as calcineurin. Our results provide an explanation for the pathogenic intervention of p.R123W mutant protein in the occurrence of hypertrophic cardiomyopathy (HCM).

Role of ATP-Small Heat Shock Protein Interaction in Human Diseases

Adenosine triphosphate (ATP) is an important fuel of life for humans and Mycobacterium species. Its potential role in modulating cellular functions and implications in systemic, pulmonary, and ocular diseases is well studied. Plasma ATP has been used as a diagnostic and prognostic biomarker owing to its close association with disease’s progression. Several stresses induce altered ATP generation, causing disorders and illnesses. Small heat shock proteins (sHSPs) are dynamic oligomers that are dominantly β-sheet in nature. Some important functions that they exhibit include preventing protein aggregation, enabling protein refolding, conferring thermotolerance to cells, and exhibiting anti-apoptotic functions. Expression and functions of sHSPs in humans are closely associated with several diseases like cataracts, cardiovascular diseases, renal diseases, cancer, etc. Additionally, there are some mycobacterial sHSPs like Mycobacterium leprae HSP18 and Mycobacterium tuberculosis HSP16.3, whose molecular chaperone functions are implicated in the growth and survival of pathogens in host species. As both ATP and sHSPs, remain closely associated with several human diseases and survival of bacterial pathogens in the host, therefore substantial research has been conducted to elucidate ATP-sHSP interaction. In this mini review, the impact of ATP on the structure and function of human and mycobacterial sHSPs is discussed. Additionally, how such interactions can influence the onset of several human diseases is also discussed.