Human alpha B-crystallin gene and preferential promoter function in lens

Human Mutated MYOT and CRYAB Genes Cause a Myopathic Phenotype in Zebrafish

Myofibrillar myopathies (MFMs) are a group of hereditary neuromuscular disorders sharing common histological features, such as myofibrillar derangement, Z-disk disintegration, and the accumulation of degradation products into protein aggregates. They are caused by mutations in several genes that encode either structural proteins or molecular chaperones. Nevertheless, the mechanisms by which mutated genes result in protein aggregation are still unknown. To unveil the role of myotilin and αB-crystallin in the pathogenesis of MFM, we injected zebrafish fertilized eggs at the one-cell stage with expression plasmids harboring cDNA sequences of human wildtype or mutated MYOT (p.Ser95Ile) and human wildtype or mutated CRYAB (p.Gly154Ser). We evaluated the effects on fish survival, motor behavior, muscle structure and development. We found that transgenic zebrafish showed morphological defects that were more severe in those overexpressing mutant genes. which developed a myopathic phenotype consistent with that of human myofibrillar myopathy, including the formation of protein aggregates. Results indicate that pathogenic mutations in myotilin and αB-crystallin genes associated with MFM cause a structural and functional impairment of the skeletal muscle in zebrafish, thereby making this non-mammalian organism a powerful model to dissect disease pathogenesis and find possible druggable targets.

Genetic Insights into Primary Restrictive Cardiomyopathy

Restrictive cardiomyopathy is a rare cardiac disease causing severe diastolic dysfunction, ventricular stiffness and dilated atria. In consequence, it induces heart failure often with preserved ejection fraction and is associated with a high mortality. Since it is a poor clinical prognosis, patients with restrictive cardiomyopathy frequently require heart transplantation. Genetic as well as non-genetic factors contribute to restrictive cardiomyopathy and a significant portion of cases are of unknown etiology. However, the genetic forms of restrictive cardiomyopathy and the involved molecular pathomechanisms are only partially understood. In this review, we summarize the current knowledge about primary genetic restrictive cardiomyopathy and describe its genetic landscape, which might be of interest for geneticists as well as for cardiologists.

Alpha B-Crystallin in Muscle Disease Prevention: The Role of Physical Activity

HSPB5 or alpha B-crystallin (CRYAB), originally identified as lens protein, is one of the most widespread and represented of the human small heat shock proteins (sHSPs). It is greatly expressed in tissue with high rates of oxidative metabolism, such as skeletal and cardiac muscles, where HSPB5 dysfunction is associated with a plethora of human diseases. Since HSPB5 has a major role in protecting muscle tissues from the alterations of protein stability (i.e., microfilaments, microtubules, and intermediate filament components), it is not surprising that this sHSP is specifically modulated by exercise. Considering the robust content and the protective function of HSPB5 in striated muscle tissues, as well as its specific response to muscle contraction, it is then realistic to predict a specific role for exercise-induced modulation of HSPB5 in the prevention of muscle diseases caused by protein misfolding. After offering an overview of the current knowledge on HSPB5 structure and function in muscle, this review aims to introduce the reader to the capacity that different exercise modalities have to induce and/or activate HSPB5 to levels sufficient to confer protection, with the potential to prevent or delay skeletal and cardiac muscle disorders.

Structural and functional studies of D109A human αB-crystallin contributing to the development of cataract and cardiomyopathy diseases

αB-crystallin (heat shock protein β5/HSPB5) is a member of the family of small heat shock proteins that is expressed in various organs of the human body including eye lenses and muscles. Therefore, mutations in the gene of this protein (CRYAB) might have many pathological consequences. A new mutation has recently been discovered in the α-crystallin domain of this chaperone protein which replaces aspartate 109 with alanine (D109A). This mutation can cause myofibrillar myopathy (MFM), cataracts, and cardiomyopathy. In the current study, several spectroscopic and microscopic analyses, as well as gel electrophoresis assessment were applied to elucidate the pathogenic contribution of human αB-crystallin bearing D109A mutation in development of eye lens cataract and myopathies. The protein oligomerization, chaperone-like activity and chemical/thermal stabilities of the mutant and wild-type protein were also investigated in the comparative assessments. Our results suggested that the D109A mutation has a significant impact on the important features of human αB-crystallin, including its structure, size of the protein oligomers, tendency to form amyloid fibrils, stability, and chaperone-like activity. Given the importance of aspartate 109 in maintaining the proper structure of the α-crystallin domain, its role in the dimerization and chaperone-like activity, as well as preserving protein stability through the formation of salt bridges; mutation at this important site might have critical consequences and can explain the genesis of myopathy and cataract disorders. Also, the formation of large light-scattering aggregates and disruption of the chaperone-like activity by D109A mutation might be considered as important contributing factors in development of the eye lens opacity.

Trends in HSPB5 research: a 36-year bibliometric analysis

HSPB5 (heat shock protein B5), also known as αB-crystallin, is one of the most widespread and populous of the ten human small heat shock proteins (sHsps). Over the past decades, extensive research has been conducted on HSPB5. However, few studies have statistically analyzed these publications. Herein, we conducted a bibliometric analysis to track the global research trend and current development status of HSPB5 research from the Web of Science Core Collection (WoSCC) database between 1985 and 2020. Our results demonstrate that 1220 original articles cited 54,778 times in 391 scholarly journals were published. Visualization analyses reveal that the Journal of Biological Chemistry was the most influential journal with 85 articles. The USA dominated this field with 520 publications (42.62%), followed by Japan with 149 publications (12.21%), and Kato contributed the largest number of publications. Most related publications were published in journals focusing on biochemistry molecular biology, cell biology, neurosciences neurology, and ophthalmology. In addition, keyword co-occurrence analyses identify three predominant research topics: expression of HSPB5, chaperone studies for HSPB5, and pathological studies of HSPB5. This study provides valuable guidance for researchers and leads to collaborative opportunities between diverse research interests to be integrated for HSPB5 research.

Function and Fiber-Type Specific Distribution of Hsp60 and αB-Crystallin in Skeletal Muscles: Role of Physical Exercise

Simple Summary

Skeletal muscle represents about 40% of the body mass in humans and it is a copious and plastic tissue, rich in proteins that are subject to continuous rearrangements. Physical exercise is considered a physiological stressor for different organs, in particular for skeletal muscle, and it is a factor able to stimulate the cellular remodeling processes related to the phenomenon of adaptation. All cells respond to various stress conditions by up-regulating the expression and/or activation of a group of proteins called heat shock proteins (HSPs). Although their expression is induced by several stimuli, they are commonly recognized as HSPs due to the first experiments showing their increased transcription after application of heat shock. These proteins are molecular chaperones mainly involved in assisting protein transport and folding, assembling multimolecular complexes, and triggering protein degradation by proteasome. Among the HSPs, a special attention needs to be devoted to Hsp60 and αB-crystallin, proteins constitutively expressed in the skeletal muscle, where they are known to be important in muscle physiopathology. Therefore, here we provide a critical update on their role in skeletal muscle fibers after physical exercise, highlighting the control of their expression, their biological function, and their specific distribution within skeletal muscle fiber-types.

Abstract

Skeletal muscle is a plastic and complex tissue, rich in proteins that are subject to continuous rearrangements. Skeletal muscle homeostasis can be affected by different types of stresses, including physical activity, a physiological stressor able to stimulate a robust increase in different heat shock proteins (HSPs). The modulation of these proteins appears to be fundamental in facilitating the cellular remodeling processes related to the phenomenon of training adaptations such as hypertrophy, increased oxidative capacity, and mitochondrial activity. Among the HSPs, a special attention needs to be devoted to Hsp60 and αB-crystallin (CRYAB), proteins constitutively expressed in the skeletal muscle, where their specific features could be highly relevant in understanding the impact of different volumes of training regimes on myofiber types and in explaining the complex picture of exercise-induced mechanical strain and damaging conditions on fiber population. This knowledge could lead to a better personalization of training protocols with an optimal non-harmful workload in populations of individuals with different needs and healthy status. Here, we introduce for the first time to the reader these peculiar HSPs from the perspective of exercise response, highlighting the control of their expression, biological function, and specific distribution within skeletal muscle fiber-types.

AlphaB-crystallin and breast cancer: role and possible therapeutic strategies

AlphaB-crystallin (HSPB5) is one of the most prominent and well-studied members of the small heat shock protein (sHsp) family. To date, it is known that this protein modulates significant cellular processes and therefore, it is not surprising that its deregulation is involved in various human pathologies, including cancer diseases. Despite the pathogenic significance of HSPB5 in cancer and its regulatory mechanism related to aggressiveness is poorly understood, several reports describe the association of breast carcinoma progression with HSPB5, whose expression is also considered an independent predictor of breast cancer metastasis to the brain. Indeed, numerous authors indicate HSPB5 as a new valuable biomarker for clinicopathological parameters and poor prognosis in breast cancer. Considering the cytoprotective, anti-apoptotic, pro-angiogenic, and pro-metastatic properties of the sHsps, it is not surprising that they are considered as promising targets for anticancer treatment, even though, at present, a deeper understanding of their mode of action is needed to allow the development of precise therapeutic interventions. Data on the direct inhibition of different sHsps demonstrate promising results in cancer pathologies; however, specific strategies against HSPB5 have not been considered. This review highlights the most relevant findings on HSPB5 and its role in breast cancer, as well as the possible strategies in using HSPB5 inhibition for therapeutic purposes.

Expression of CRYAB with the angiogenesis and poor prognosis for human gastric cancer

Alpha-B crystallin (CRYAB), as a small heat shock protein, has been found to be highly expressed in various human cancers and significantly associated with the unfavorable prognosis of these tumor. Nevertheless, the clinical significance of CRYAB in gastric cancer (GC) angiogenesis remains to be elucidated. In this study, we evaluated the expression of CRYAB and CD34 in GC tissues and corresponding normal gastric specimens to explore whether high level CRYAB is related with the angiogenesis and the poor prognosis in GC.In this study, the expression of CRYAB and CD34 were detected in GC tissues and corresponding normal gastric tissues by immunohistochemical (IHC) technique. Furthermore, the relationship of CRYAB with CD34-evaluated microvessel density (MVD) and poor prognosis was also investigated.CRYAB expression level was significantly higher in GC tissue than in normal gastric mucosa tissue, and clearly mean higher MVD was observed in tumor tissues compared with non-cancerous tissues. Besides, higher MVD value was observed in positive CRYAB expression group than in negative CRYAB expression group. Statistical analysis showed that CRYAB and MVD are associated with clinicopathological features including lymph node metastasis (LNM), tumor differentiation, invasion depth, and TNM stages. Kaplan-Meier method and multivariate survival analysis indicated that high expression of CRYAB, MVD, invasion depth, TNM stages, and tumor differentiation, as well as LNM significantly correlate with poor prognosis of GC patients.High expression of CRYAB may contribute to angiogenesis, invasion and metastasis of GC. These results indicated that CRYAB was expected to be a promising molecular marker for poor prognosis and potential therapeutic target in patients with GC.

The role of αB-crystallin in skeletal and cardiac muscle tissues

All organisms and cells respond to various stress conditions such as environmental, metabolic, or pathophysiological stress by generally upregulating, among others, the expression and/or activation of a group of proteins called heat shock proteins (HSPs). Among the HSPs, special attention has been devoted to the mutations affecting the function of the αB-crystallin (HSPB5), a small heat shock protein (sHsp) playing a critical role in the modulation of several cellular processes related to survival and stress recovery, such as protein degradation, cytoskeletal stabilization, and apoptosis. Because of the emerging role in general health and disease conditions, the main objective of this mini-review is to provide a brief account on the role of HSPB5 in mammalian muscle physiopathology. Here, we report the current known state of the regulation and localization of HSPB5 in skeletal and cardiac tissue, making also a critical summary of all human HSPB5 mutations known to be strictly associated to specific skeletal and cardiac diseases, such as desmin-related myopathies (DRM), dilated (DCM) and restrictive (RCM) cardiomyopathy. Finally, pointing to putative strategies for HSPB5-based therapy to prevent or counteract these forms of human muscular disorders.

Alpha B-crystallin promotes the invasion and metastasis of gastric cancer via NF-κB-induced epithelial-mesenchymal transition

Alpha B‐crystallin (CRYAB) is overexpressed in a variety of cancers. However, little is known about its specific function and regulatory mechanism in gastric cancer. Here, we first explore the role of CRYAB in gastric cancer progression and metastasis. The expression of CRYAB was determined by western blot and immunohistochemistry in gastric cancer tissues. Besides, methods including stably transfected against CRYAB into gastric cancer cells, western blot, migration and invasion assays in vitro and metastasis assay in vivo were also conducted. The expression of CRYAB is up‐regulated in gastric cancer tissues compared with matched normal tissues. High expression level of CRYAB is closely correlated with cancer metastasis and shorter survival time in patients with gastric cancer. Additionally, CRYAB silencing significantly suppresses epithelial‐mesenchymal transition (EMT), migration and invasion of gastric cancer cells in vitro and in vivo, whereas CRYAB overexpression dramatically reverses these events. Mechanically, CRYAB facilitates gastric cancer cells invasion and metastasis via nuclear factor‐κ‐gene binding (NF‐κB)‐regulated EMT. These findings suggest that CRYAB expression predicts a poor prognosis in patients with gastric cancer. Besides, CRYAB contributes to gastric cancer cells migration and invasion via EMT, mediated by the NF‐κB signalling pathway, thus possibly providing a novel therapeutic target for gastric cancer.

A novel dominant D109A CRYAB mutation in a family with myofibrillar myopathy affects αB-crystallin structure

Myofibrillar myopathy (MFM) is a group of inherited muscular disorders characterized by myofibrils dissolution and abnormal accumulation of degradation products. So far causative mutations have been identified in nine genes encoding Z-disk proteins, including αB-crystallin (CRYAB), a small heat shock protein (also called HSPB5). Here, we report a case study of a 63-year-old Polish female with a progressive lower limb weakness and muscle biopsy suggesting a myofibrillar myopathy, and extra-muscular multisystemic involvement, including cataract and cardiomiopathy. Five members of the proband's family presented similar symptoms. Whole exome sequencing followed by bioinformatic analysis revealed a novel D109A mutation in CRYAB associated with the disease. Molecular modeling in accordance with muscle biopsy microscopic analyses predicted that D109A mutation influence both structure and function of CRYAB due to decreased stability of oligomers leading to aggregate formation. In consequence disrupted sarcomere cytoskeleton organization might lead to muscle pathology. We also suggest that mutated RQDE sequence of CRYAB could impair CRYAB chaperone-like activity and promote aggregation of lens crystallins.

Slow recovery of the impaired fatigue resistance in postunloading mouse soleus muscle corresponding to decreased mitochondrial function and a compensatory increase in type I slow fibers

Unloading or disuse rapidly results in skeletal muscle atrophy, switching to fast-type fibers, and decreased resistance to fatigue. The recovery process is of major importance in rehabilitation for various clinical conditions. Here we studied mouse soleus muscle during 60 days of reloading after 4 wk of hindlimb suspension. Unloading produced significant atrophy of soleus muscle with decreased contractile force and fatigue resistance, accompanied by switches of myosin isoforms from IIa to IIx and IIb and fast troponin T to more low-molecular-weight splice forms. The total mass, fiber size, and contractile force of soleus muscle recovered to control levels after 15 days of reloading. However, the fatigue resistance showed a trend of worsening during this period with significant infiltration of inflammatory cells at days 3 and 7, indicating reloading injuries that were accompanied by active regeneration with upregulations of filamin-C, αB-crystallin, and desmin. The fatigue resistance partially recovered after 30-60 days of reloading. The expression of peroxisome proliferator-activated receptor γ coactivator 1α and mitofusin-2 showed changes parallel to that of fatigue resistance after unloading and during reloading, suggesting a causal role of decreased mitochondrial function. Slow fiber contents in the soleus muscle were increased after 30-60 days of reloading to become significantly higher than the normal level, indicating a secondary adaption to compensate for the slow recovery of fatigue resistance.

Missense Mutations in CRYAB Are Liable for Recessive Congenital Cataracts

PURPOSE

This study was initiated to identify causal mutations responsible for autosomal recessive congenital cataracts in consanguineous familial cases.

METHODS

Affected individuals underwent a detailed ophthalmological and clinical examination, and slit-lamp photographs were ascertained for affected individuals who have not yet been operated for the removal of the cataractous lens. Blood samples were obtained, and genomic DNA was extracted from white blood cells. A genome-wide scan was completed with short tandem repeat (STR) markers, and the logarithm of odds (LOD) scores were calculated. Protein coding exons of CRYAB were sequenced, bi-directionally. Evolutionary conservation was investigated by aligning CRYAB orthologues, and the expression of Cryab in embryonic and postnatal mice lens was investigated with TaqMan probe.

RESULTS

The clinical and ophthalmological examinations suggested that all affected individuals had nuclear cataracts. Genome-wide linkage analysis suggested a potential region on chromosome 11q23 harboring CRYAB. DNA sequencing identified a missense variation: c.34C>T (p.R12C) in CRYAB that segregated with the disease phenotype in the family. Subsequent interrogation of our entire cohort of familial cases identified a second familial case localized to chromosome 11q23 harboring a c.31C>T (p.R11C) mutation. In silico analyses suggested that the mutations identified in familial cases, p.R11C and p.R12C will not be tolerated by the three-dimensional structure of CRYAB. Real-time PCR analysis identified the expression of Cryab in mouse lens as early as embryonic day 15 (E15) that increased significantly until postnatal day 6 (P6) with steady level of expression thereafter.

CONCLUSION

Here, we report two novel missense mutations, p.R11C and p.R12C, in CRYAB associated with autosomal recessive congenital nuclear cataracts.

αB-Crystallin R120G variant causes cardiac arrhythmias and alterations in the expression of Ca(2+) -handling proteins and endoplasmic reticulum stress in mice

Mutations of αB-crystallin (CryαB), a small heat shock protein abundantly expressed in cardiac and skeletal muscles, are known to cause desmin-related myopathies. The CryαB R120G allele has been linked to a familial desminopathy and, in transgenic mice, causes a sudden death at about 28 weeks of age. To investigate the mechanisms of the sudden cardiac arrest of CryαB R120G transgenic mice, we prepared protein samples from left ventricular tissues of two different age groups (10 and 28 weeks) and examined Ca(2+) -handling proteins. Expression of sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) 2, phospholamban, ryanodine receptor 2 and calsequestrin 2 was significantly decreased in 28- versus 10-week-old CryαB R120G transgenic mice. In addition, low heart rate variability, including heart rate, total power and low frequency, was observed and continuous electrocardiogram monitoring revealed cardiac arrhythmias, such as ventricular tachycardia, atrioventricular block and atrial flutter, in 28-week-old CryαB R120G transgenic mice. In contrast, expression of endoplasmic reticulum (ER) degradation enhancing α-mannosidase-like protein, inositol requirement 1 and X-box binding protein 1 were increased significantly in 28- versus 10-week-old CryαBR120G transgenic mice, suggesting that the CryαBR120G transgenic mice exhibit increased ER stress compared with wild-type mice. Together, the data suggest that the CryαB R120G dominant variant induces ER stress and impairs Ca(2+) regulation, leading to ageing-related cardiac dysfunction, arrhythmias and decreased autonomic tone with shortened lifespan.

Drosophila small heat shock protein CryAB ensures structural integrity of developing muscles, and proper muscle and heart performance

Molecular chaperones, such as the small heat shock proteins (sHsps), maintain normal cellular function by controlling protein homeostasis in stress conditions. However, sHsps are not only activated in response to environmental insults, but also exert developmental and tissue-specific functions that are much less known. Here, we show that during normal development the Drosophila sHsp CryAB [L(2)efl] is specifically expressed in larval body wall muscles and accumulates at the level of Z-bands and around myonuclei. CryAB features a conserved actin-binding domain and, when attenuated, leads to clustering of myonuclei and an altered pattern of sarcomeric actin and the Z-band-associated actin crosslinker Cheerio (filamin). Our data suggest that CryAB and Cheerio form a complex essential for muscle integrity: CryAB colocalizes with Cheerio and, as revealed by mass spectrometry and co-immunoprecipitation experiments, binds to Cheerio, and the muscle-specific attenuation of cheerio leads to CryAB-like sarcomeric phenotypes. Furthermore, muscle-targeted expression of CryAB(R120G), which carries a mutation associated with desmin-related myopathy (DRM), results in an altered sarcomeric actin pattern, in affected myofibrillar integrity and in Z-band breaks, leading to reduced muscle performance and to marked cardiac arrhythmia. Taken together, we demonstrate that CryAB ensures myofibrillar integrity in Drosophila muscles during development and propose that it does so by interacting with the actin crosslinker Cheerio. The evidence that a DRM-causing mutation affects CryAB muscle function and leads to DRM-like phenotypes in the fly reveals a conserved stress-independent role of CryAB in maintaining muscle cell cytoarchitecture.

Proteomic analysis of laser capture microscopy purified myotendinous junction regions from muscle sections

The myotendinous junction is a specialized structure of the muscle fibre enriched in mechanosensing complexes, including costameric proteins and core elements of the z-disc. Here, laser capture microdissection was applied to purify membrane regions from the myotendinous junctions of mouse skeletal muscles, which were then processed for proteomic analysis. Sarcolemma sections from the longitudinal axis of the muscle fibre were used as control for the specificity of the junctional preparation. Gene ontology term analysis of the combined lists indicated a statistically significant enrichment in membrane-associated proteins. The myotendinous junction preparation contained previously uncharacterized proteins, a number of z-disc costameric ligands (e.g., actinins, capZ, αB cristallin, filamin C, cypher, calsarcin, desmin, FHL1, telethonin, nebulin, titin and an enigma-like protein) and other proposed players of sarcomeric stretch sensing and signalling, such as myotilin and the three myomesin homologs. A subset were confirmed by immunofluorescence analysis as enriched at the myotendinous junction, suggesting that laser capture microdissection from muscle sections is a valid approach to identify novel myotendinous junction players potentially involved in mechanotransduction pathways.

Cell-type-dependent access of HSF1 and HSF4 to αB-crystallin promoter during heat shock

Epithelial cells and fibroblasts both express heat shock transcription factors, HSF1 and HSF4, yet they respond to heat shock differentially. For example, while HSP70 is induced in both cell types, the small heat shock protein, αB-crystallin gene (CRYAB) that contains a canonical heat shock promoter, is only induced in fibroblasts. A canonical heat shock promoter contains three or more inverted repeats of the pentanucleotide 5'-nGAAn-3' that make the heat shock element. It is known that, in vitro, promoter architecture (the order and spacing of these repeats) impacts the interaction of various heat shock transcription factors (HSFs) with the heat shock promoter, but in vivo relevance of these binding preferences so far as the expression is concerned is poorly understood. In this report, we first establish cell-type-dependent differential expression of CRYAB in four established cell lines and then working with adult human retinal pigment epithelial cells and NIH3T3 fibroblasts and employing chromatin immunoprecipitation, attempt to relate expression to promoter occupancy by HSF1 and HSF4. We show that HSF4 occupies only CRYAB and not HSP70 promoter in epithelial cells, while HSF1 occupies only HSP70 promoter in both cell types, and cryab promoter, only in heat shocked fibroblasts; HSF4, on the other hand, is never seen on these two promoters in NIH3T3 fibroblasts. This comparative analysis with CRYAB and HSP70 demonstrates that differential heat shock response is controlled by cell-type-dependent access of HSFs (HSF1 and HSF4) to specific promoters, independent of the promoter architecture.

Crystallin distribution patterns in Litoria infrafrenata and Phyllomedusa sauvagei lenses

The eye lens remains transparent because of soluble lens proteins known as crystallins. For years γ-crystallins have been known as the main lens proteins in lower vertebrates such as fish and amphibians. The unique growth features of the lens render it an ideal structure to study ageing; few studies have examined such changes in anuran lenses. This study aimed to investigate protein distribution patterns in Litoria infrafrenata and Phyllomedusa sauvagei species. Lenses were fractionated into concentric layers by controlled dissolution. Water-soluble proteins were separated into high (HMW), middle (MMW) and low molecular weight (LMW) fractions by size-exclusion HPLC and constituents of each protein class revealed by 1DE and 2DE. Spots were selected from 2DE gels on the basis of known ranges of subunit molecular weights and pH ranges and were identified by MALDI-TOF/TOF MS following trypsin digestion. Comparable lens distribution patterns were found for each species studied. Common crystallins were detected in both species; the most prominent of these was γ-crystallin. Towards the lens centre, there was a decrease in α- and β-crystallin proportions and an increase in γ-crystallins. Subunits representing taxon-specific crystallins demonstrating strong sequence homology with ζ-crystallin/quinone oxidoreductase were found in both L. infrafrenata and P. sauvagei lenses. Further work is needed to determine which amphibians have taxon-specific crystallins, their evolutionary origins, and their function.

Mutations in human αA-crystallin/sHSP affect subunit exchange interaction with αB-crystallin

Background

Mutation in αA-crystallin contributes to the development of congenital cataract in humans. Heterooligomerization of αA-crystallin and αB-crystallin is essential for maintaining transparency in the eye lens. The effect of congenital cataract causing mutants of αA-crystallin on subunit exchange and interaction with αB-crystallin is unknown. In the present study, interaction of the mutants of αA-crystallin with αB-crystallin was studied both in vitro and in situ by the fluorescence resonance energy transfer (FRET) technique.

Methodology/Principal Findings

In vitro FRET technique was used to demonstrate the rates of subunit exchange of αB-wt with the following αA-crystallin mutants: R12C, R21L, R21W, R49C, R54C, and R116C. The subunit exchange rates (k values) of R21W and R116C with αB-wt decreased drastically as compared to αA-wt interacting with αB-wt. Moderately decreased k values were seen with R12C, R49C and R54C while R21L showed nearly normal k value. The interaction of αA- mutants with αB-wt was also assessed by in situ FRET. YFP-tagged αA mutants were co-expressed with CFP-tagged αB-wt in HeLa cells and the spectral signals were captured with a confocal microscope before and after acceptor laser photobleaching. The interaction of R21W and R116C with αB-wt was decreased nearly 50% as compared to αA-wt while the rest of the mutants showed slightly decreased interaction. Thus, there is good agreement between the in vitro and in situ FRET data.

Conclusions/Significance

Structural changes occurring in these mutants, as reported earlier, could be the underlying cause for the decreased interaction with αB may contribute to development of congenital cataract.

Synergistic efficacy of LBH and alphaB-crystallin through inhibiting transcriptional activities of p53 and p21

LBH is a transcription factor as a candidate gene for CHD associated with partial trisomy 2p syndrome. To identify potential LBH-interacting partners, a yeast two-hybrid screen using LBH as a bait was performed with a human heart cDNA library. One of the clones identified encodes alphaB-crystallin. Co-immunoprecipitation and GST pull-down assays showed that LBH interacts with alphaB-crystallin, which is further confirmed by mammalian two-hybrid assays. Co-localization analysis showed that in COS-7 cells, alphaB-crystallin that is cytoplasmic alone, accumulates partialy in the nucleus when co-transfected with LBH. Transient transfection assays indicated that overexpression of LBH or alphaB-crystallin reduced the transcriptional activities of p53 and p21, respectively, Overexpression of both alphaB-crystallin and LBH together resulted in a stronger repression of the transcriptional activities of p21 and p53. These results showed that the interaction of LBH and alphaB-crystallin may inhibit synergistically the transcriptional regulation of p53 and p21.

Desmin-related myopathy

Desmin-related myopathy (DRM) is an autosomally inherited skeletal and cardiac myopathy, mainly caused by dominant mutations in the desmin gene (DES). We provide (i) a literature review on DRM, including clinical manifestations, inheritance, molecular genetics, myopathology and management and (ii) a meta-analysis of reported DES mutation carriers, focusing on their clinical characteristics and potential genotype-phenotype correlations. Meta-analysis: DES mutation carriers (n = 159) with 40 different mutations were included. Neurological signs were present in 74% and cardiological signs in 74% of carriers (both neurological and cardiological signs in 49%, isolated neurological signs in 22%, and isolated cardiological signs in 22%). More than 70% of carriers exhibited myopathy or muscular weakness, with normal creatine kinase levels present in one third of them. Up to 50% of carriers had cardiomyopathy and around 60% had cardiac conduction disease or arrhythmias, with atrioventricular block as an important hallmark. Symptoms generally started during the 30s; a quarter of carriers died at a mean age of 49 years. Sudden cardiac death occurred in two patients with a pacemaker, suggesting a ventricular tachyarrhythmia as cause of death. The majority of DES mutations were missense mutations, mostly located in the 2B domain. Mutations in the 2B domain were predominant in patients with an isolated neurological phenotype, whereas head and tail domain mutations were predominant in patients with an isolated cardiological phenotype.

alphaB-crystallin: a novel p53-target gene required for p53-dependent apoptosis

The p53 protein is a transcription factor that trans-activates various genes in response to DNA-damaging stress. To search for new p53-target genes, we applied a cDNA microarray system using two independent p53-inducible cell lines, followed by in silico analysis to detect p53 response elements. Here, we report on crystallin alpha B gene (CRYAB), which encodes alphaB-crystallin, and is one of the genes directly trans-activated by p53. We confirmed it is directly transcribed by p53 using promoter analysis, deletion reporter assay, ChIP assay and EMSA. alphaB-crystallin is also upregulated in a p53-dependent manner and binds to the DNA-binding domain of p53. Overexpression of alphaB-crystallin increased p53 protein and, in contrast, repression of alphaB-crystallin decreased p53 protein. Interestingly, both overexpression and repression of alphaB-crystallin reduced p53-dependent apoptosis. In conclusion, we identified that alphaB-crystallin was a novel p53-target gene and required for p53-dependent apoptosis using two independent p53-inducible cell lines. This is the first report associating p53 directly with a heat shock protein through trans-activation and physical interaction.

Tragedy in a heartbeat: malfunctioning desmin causes skeletal and cardiac muscle disease

Muscle fiber deterioration resulting in progressive skeletal muscle weakness, heart failure, and respiratory distress occurs in more than 20 inherited myopathies. As discussed in this Review, one of the newly identified myopathies is desminopathy, a disease caused by dysfunctional mutations in desmin, a type III intermediate filament protein, or alphaB-crystallin, a chaperone for desmin. The range of clinical manifestations in patients with desminopathy is wide and may overlap with those observed in individuals with other myopathies. Awareness of this disease needs to be heightened, diagnostic criteria reliably outlined, and molecular testing readily available; this would ensure prevention of sudden death from cardiac arrhythmias and other complications.

Two hsp23 genes in the Mediterranean fruit fly, Ceratitis capitata: structural characterization, heat shock regulation and developmental expression

In the present study, we characterized a 3320-bp genomic DNA fragment encoding two medfly (Ceratitis capitata) homologues of the Drosophila melanogaster heat shock protein 23 (hsp23) gene, named Cchsp23-alphaand -beta. The two medfly hsp23 genes are transcribed in opposite directions and encode two almost identical proteins. Furthermore, the two genes exhibit a very high degree of similarity in their 5' untranslated and proximal promoter regions. Phylogenetic analysis indicated that the CcHsp23 proteins are orthologous to Drosophila Hsp23 and Sarcophaga crassipalpis Hsp23. Structural analysis of the 5' flanking regions of the Cchsp23 genes revealed the presence of several putative heat shock elements. Both CcHsp23 genes are induced by heat in a similar manner. In addition to heat-induction, the Cchsp23 genes are expressed at several stages of normal development as well as in ovaries and testes. In general, the developmental expression patterns of the medfly genes are similar, suggesting that they are under similar regulatory mechanisms. However, the expression of the Cchsp23 genes differs significantly from the expression of the Drosophila hsp23 gene in certain embryonic and larval stages, suggesting differential regulation of the hsp23 genes in the two dipteran species. The expression of both Cchsp23 genes in adult flies is increased with age, especially in males.

The hsp27 gene of the Mediterranean fruit fly, Ceratitis capitata: structural characterization, regulation and developmental expression

In the present study, a genomic DNA clone encoding the medfly homolog of Drosophila melanogaster hsp27 gene, named Cchsp27, was isolated. We sequenced a part of the clone containing the coding region, the 5' untranslated region and approximately 2.8 Kb of the 5' flanking region of the gene. Phylogenetic analysis of several insect small heat shock proteins, suggested that CcHsp27 is orthologous to Drosophila Hsp27 and Sarcophaga crassipalpis Hsp25. The Cchsp27 gene was mapped at the 81A division of the sixth chromosome which coincides with one of the major heat shock puffs of medfly. Structural analysis of the 5' flanking region of the Cchsp27 gene revealed the presence of five putative heat shock elements and one putative ecdysone response element. In addition to heat induction, the Cchsp27 gene was expressed at several stages of normal medfly development. In general, the developmental expression pattern of the Cchsp27 gene was similar to the respective pattern of Drosophila hsp27 gene. However, there were some important differences in certain developmental stages suggesting differential regulation of the hsp27 gene in the two dipterans species. Salivary gland culture experiments showed that the Cchsp27 gene is regulated by 20-hydroxyecdysone.

Differential rate constants of racemization of aspartyl and asparaginyl residues in human alpha A-crystallin mutants

Asp58 and Asp151 in alpha A-crystallin of human eye lenses become highly inverted and isomerized to d-beta-Asp residues with age. Racemization was previously shown to proceed rapidly when the residue on the carboxyl side of the Asp residue is small. Asn was also demonstrated to be more susceptible to racemization than Asp in protein. In this study, the changes of rate constants for racemization at Asp58 and Asp151 and at Asn58 and Asn151 were investigated using D58N, S59T, D151N and A152V mutants obtained through site-directed mutagenesis. The rate constant of racemization at Asn151 in D151N was found to be 1.5 times more rapid than Asp151 in the wild-type. For A152V, the rate constant at Asp151 was 1/4 that of the wild-type. There were no significant differences in the rate constants of racemization for both Asp58 and Asn58 residues. The aggregate size of D58N, S59T and D151N mutants increased or increased in polydispersity and their chaperone activities decreased. The size and chaperone activity of A152V was unchanged. These results suggest that structures close to Asp58 and Asp151 residues in the protein affect the rate constant of Asp racemization and the size and chaperone function of alpha A-crystallin.

Intermediate filament diseases: desminopathy

Desminopathy is one of the most common intermediate filament human disorders associated with mutations in closely interacting proteins, desmin and alphaB-crystallin. The inheritance pattern in familial desminopathy is characterized as autosomal dominant or autosomal recessive, but many cases have no family history. At least some and likely most sporadic desminopathy cases are associated with de novo DES mutations. The age of disease onset and rate of progression may vary depending on the type of inheritance and location of the causative mutation. Typically, the illness presents with lower and later upper limb muscle weakness slowly spreading to involve truncal, neck-flexor, facial and bulbar muscles. Skeletal myopathy is often combined with cardiomyopathy manifested by conduction blocks, arrhythmias and chronic heart failure resulting in premature sudden death. Respiratory muscle weakness is a major complication in some patients. Sections of the affected skeletal and cardiac muscles show abnormal fibre areas containing chimeric aggregates consisting of desmin and other cytoskeletal proteins. Various DES gene mutations: point mutations, an insertion, small in-frame deletions and a larger exon-skipping deletion, have been identified in desminopathy patients. The majority of these mutations are located in conserved alpha-helical segments, but additional mutations have recently been identified in the tail domain. Filament and network assembly studies indicate that most but not all disease-causing mutations make desmin assembly-incompetent and able to disrupt a pre-existing filamentous network in dominant-negative fashion. AlphaB-crystallin serves as a chaperone for desmin preventing its aggregation under various forms of stress; mutant CRYAB causes cardiac and skeletal myopathies identical to those resulting from DES mutations.

Degradation of C-terminal truncated alpha A-crystallins by the ubiquitin-proteasome pathway

PURPOSE

Calpain-mediated C-terminal cleavage of alpha A-crystallins occurs during aging and cataractogenesis. The objective of the present study was to explore the role of the ubiquitin-proteasome pathway (UPP) in degrading C-terminal truncated alpha A-crystallins.

METHODS

Recombinant wild-type (wt) alpha A-crystallin and C-terminal truncated alpha A(1-168)-, alpha A(1-163)-, and alpha A(1-162)-crystallins were expressed in Escherichia coli and purified to homogeneity. The wt and truncated alpha A-crystallins were labeled with (125)I, and proteolytic degradation was determined using both lens fiber lysate and reticulocyte lysate as sources of ubiquitinating and proteolytic enzymes. Far UV circular dichroism, tryptophan fluorescence intensity, and binding to the hydrophobic fluorescence probe Bis-ANS were used to characterize the wt and truncated alpha A-crystallins. Oligomer sizes of these crystallins were determined by multiangle light-scattering.

RESULTS

Whereas wt alpha A-crystallin was degraded moderately in both lens fiber and reticulocyte lysates, alpha A(1-168)-crystallin was resistant to degradation. The susceptibility of alpha A(1-163)-crystallin to degradation was comparable to that of wt alpha A-crystallin. However, alpha A(1-162)-crystallin was much more susceptible than wt alpha A-crystallin to degradation in both lens fiber and reticulocyte lysates. The degradation of both wt and C-terminal truncated alpha A(1-162)-crystallins requires adenosine triphosphate (ATP) and was stimulated by addition of a ubiquitin-conjugating enzyme, Ubc4. The degradation was substantially inhibited by the proteasome inhibitor MG132 and a dominant negative mutant of ubiquitin, K6W-Ub, indicating that at least part of the proteolysis was mediated by the UPP. Spectroscopic analyses of wt and C-terminal truncated alpha A-crystallins revealed that C-terminal truncation of alpha A-crystallin resulted in only subtle changes in secondary structures. However, C-terminal truncations resulted in significant changes in surface hydrophobicity and thermal stability. Thus, these conformational changes may reveal or mask the signals for the ubiquitin-dependent degradation.

CONCLUSIONS

The present data demonstrate that C-terminal cleavage of alpha A-crystallin not only alters its conformation and thermal stability, but also its susceptibility to degradation by the UPP. The rapid degradation of alpha A(1-162) by the UPP may prevent its accumulation in the lens.

C-Terminal truncation affects subunit exchange of human alphaA-crystallin with alphaB-crystallin

In human lenses, C-terminal cleavage of alphaA-crystallin at residues 172,168, and 162 have been reported. The effect of C-terminal truncation of alphaA-crystallin on subunit exchange and heterooligomer formation with alphaB-crystallin and homooligomer formation with native alphaA-crystallin is not known. We have conducted fluorescence resonance energy transfer studies which have shown that the rates of subunit exchange of alphaA(1-172 )and alphaA(1-168 )with alphaB-wt were two-fold lower than for alphaA-wt interacting with alphaB-wt. The subunit exchange rate between alphaA(1-162) and alphaB-wt was six-fold lower. These data suggest that cleavage of the C-terminal residues could significantly affect heterooligomerization. On the other hand, the subunit exchange rates between alphaA-wt and the truncated alphaA-crystallins were either unchanged or only slightly decreased, which suggest that homooligomerization may not be significantly influenced by C-terminal truncation. The main conclusion from this study is that cleavage of C-terminal residues of alphaA-crystallin including the nine residues of the flexible tail is expected to significantly affect the formation of heteroaggregates. Reconstitution experiments showed that the presence of an intact C-terminus is essential for the formation of fully integrated heteroaggregates with equal proportion of alphaA and alphaB subunits.

Interruption of CryAB-Amyloid Oligomer Formation by HSP22

An R120G missense mutation in alpha-B-crystallin (CryAB), a small heat-shock protein (HSP), causes a desmin-related cardiomyopathy (DRM) that is characterized by the formation of aggregates containing CryAB and desmin. The mutant CryAB protein leads to the formation of inclusion bodies, which contain amyloid oligomer intermediates (amyloid oligomer) in the cardiomyocytes. To further address the underlying mechanism(s) of amyloid oligomer formation in DRM linked to the CryAB R120G, a recombinant CryAB R120G protein was generated. The purified CryAB R120G protein can form a toxic amyloid oligomer, whereas little immunoreactivity was observed in the wild-type CryAB protein. A native PAGE showed that the oligomerized form was present in the CryAB R120G protein, whereas only a high molecular mass was detected in the wildtype CryAB. The oligomerized CryAB R120G of around 240-480 kDa showed strong positive immunoreactivity against an anti-oligomer antibody. The CryAB R120G amyloid oligomer was unstable and easily lost its conformation by beta-mercaptoethanol and SDS. Recombinant HSP25 or HSP22 proteins can directly interrupt oligomer formation by the CryAB R120G protein, whereas the amyloid oligomer is still present in the mixture of the wild-type CryAB and CryAB R120G proteins. This interruption by HSP25 and HSP22 was confirmed in a cardiomyocyte-based study using an adenoviral transfection system. Blockade of amyloid oligomer formation by HSP25 and HSP22 recovered the ubiquitin proteosomal activity and cellular viability. Blockade of oligomer formation by small HSP may be a new therapeutic strategy for treating DRM as well as other types of amyloid-based degenerative diseases.

Differential susceptibility of alpha A- and alpha B-crystallin to gamma-ray irradiation

Alpha-crystallin, a major protein of all vertebrate lenses, consists of two different subunits, alpha A and alpha B, which form polymeric aggregates with an average molecular mass of 300-800 kDa. Both the alpha A and alpha B subunit have a molecular mass of about 20 kDa. It is not known why alpha crystallin aggregates comprise two different subunits, given that the physicochemical properties of these proteins are very similar. The present study compares the susceptibility of the alpha A and alpha B subunits to gamma-rays. We prepared a recombinant form of human alpha A- and alpha B-crystallin and then irradiated the proteins with gamma-rays. Based on far-UV CD spectra, alpha A-crystallin retained beta-sheet conformation after gamma irradiation up to 3.0 kGy, whereas alpha B-crystallin lost beta-sheet conformation upon exposure to gamma irradiation at >1.0 kGy. Size exclusion chromatography showed that the aggregation and polydispersity of recombinant alpha A-crystallin increased slightly after >1.0 kGy irradiation. In contrast, irradiation of alpha B-crystallin at 1.0 kGy resulted in the formation of huge aggregates and a marked increase in heterogeneity. We have also compared the chaperone activities of gamma-irradiated alpha A- and alpha B-crystallin aggregates. The activity of irradiated alpha A-crystallin was retained while that of the irradiated alpha B-crystallin was became inactive after irradiation of >0.5 kGy. Our results indicate that alpha A-crystallin is more stable to gamma irradiation than alpha B-crystallin.

Kinetic study of racemization of aspartyl residues in recombinant human αA-crystallin

Asp58 and Asp151 in human lens alphaA-crystallin invert and isomerize to d-beta-aspartyl residues with age. Here, we report that the racemization rate constants (k) of Asp58 and Asp151 residues in human recombinant alphaA-crystallin at 37 degrees C are 3.72 +/- 0.8 x 10(-4) and 10.7 +/- 0.7 x 10(-4)/day, respectively. The activation energy of racemization of Asp58 and Asp151 in the protein was 27.0 +/- 0.5 kcal/mol and 21.0 +/- 0.5 kcal/mol, respectively. The time required for the D/L ratio of Asp58 and Asp151 to approximate to 1.0 (D/L ratio of Asp = 0.99) at 37 degrees C was estimated as 20.9 +/- 3.7 and 6.80 +/- 0.4 years, respectively. Thus, Asp151 is more susceptible to racemization than Asp58, consistent with data from short model peptides. However, the racemization rates of both Asp58 and Asp151 residues in the protein were twice as rapid as in model peptides. These results indicate that the racemization of Asp residues in alphaA-crystallin may be influenced not only by the primary structure but also by the higher order structure around Asp residues in the protein.

Differential expression of alphaB-crystallin and Hsp27-1 in anaplastic thyroid carcinomas because of tumor-specific alphaB-crystallin gene (CRYAB) silencing

Expression of the small heat shock protein alphaB-crystallin in differentiated thyroid tumors has been described recently. In this study, we investigated the molecular mechanisms that affect the expression of alphaB-crystallin in benign goiters (n = 7) and highly malignant anaplastic thyroid carcinomas (ATCs) (n = 3). AlphaB-crystallin expression was compared with that of Hsp27-1. Immunoblot and quantitative real-time (RT) polymerase chain reaction revealed marked downregulation of alphaB-crystallin in all the tested ATCs and the ATC-derived cell line C-643 . In contrast, considerable expression of Hsp27-1 in benign and malignant thyroid tissue was demonstrated. Immunofluorescence analysis revealed no relevant topological differences between benign and malignant thyrocytes in the cytoplasmic staining of both proteins. Consistent and marked downregulation of TFCP2L1 was identified as one of the main mechanisms contributing to CRYAB gene silencing in ATCs. In addition, CRYAB gene promoter methylation seems to occur in distinct ATCs. In silico analysis revealed that the differential expression of alphaB-crystallin and Hsp27-1 results from differences between the alphaB-crystallin and Hsp27-1 promoter fragments (712 bp upstream from the transcriptional start site). Biological activity of the analyzed promoter element is confirmed by its heat shock inducibility. In conclusion, we demonstrate downregulation of alphaB-crystallin expression in highly dedifferentiated ATCs because of a tumor-specific transcription factor pattern. The differential expression of alphaB-crystallin and Hsp27-1 indicates functional differences between both proteins.

The reaction of alpha-crystallin with the cross-linker 3,3'-dithiobis(sulfosuccinimidyl propionate) demonstrates close proximity of the C termini of alphaA and alphaB in the native assembly

The chaperone-like activity of human lens alpha-crystallin in inhibiting the aggregation of denatured proteins suggests a role for alpha-crystallin in cataract prevention. Although a variety of techniques have generated structural information relevant to its chaperone-like activity, the size and heterogeneity of alpha-crystallin have prevented determination of its crystal structure. Even though synthetic cross-linkers have provided considerable information about protein structures, they have not previously been used to study the proximity and orientation of subunits within human alpha-crystallin. Cross-linkers provide structural insight into proteins by binding the side chains of amino acids within close proximity. To identify the cross-linked residues, the modified protein is digested and the resulting peptides are analyzed by mass spectrometry. Analysis of products from the reaction of alpha-crystallin with 3,3'dithiobis(sulfosuccinimidyl propionate), DTSSP, identified several modifications to both alphaA and alphaB. The most structurally informative of these modifications was a cross-link between lysine 166 of alphaA and lysine 175 of alphaB. This cross-link provides experimental evidence supporting theoretical structural models that place the C termini of alphaA and alphaB within close proximity in the native aggregate.

High prevalence of autoreactive, neuroantigen-specific CD8+ T cells in multiple sclerosis revealed by novel flow cytometric assay

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system (CNS) with features suggestive of T-cell-mediated pathology. Most prior reports have focused on CD4(+) T cells with the underlying assumption that MS is predominantly a CD4(+) T helper 1 (Th1)-mediated disease. In this report, we used a novel flow cytometric approach to evaluate autoreactive T-cell responses against a large variety of neuroantigenic targets. We found that both CD4(+) and CD8(+) T cells targeted against several CNS autoantigens were widely prevalent in patients with MS and healthy individuals. Whereas the distribution of CD4(+) responses was similar in different groups, patients with relapsing-remitting MS showed a higher proportion of CNS-specific CD8(+) responses. Autoreactive CD4(+) T cells from patients with MS exhibited a more differentiated Th1 phenotype compared with healthy subjects. Similarly, CNS-specific CD8(+) T-cell responses from patients with MS were functionally distinct from those in healthy individuals. Collectively, these studies reveal the high prevalence of class I-restricted autoreactive CD8(+) T-cell responses in MS that has been underappreciated thus far. The results emphasize the need to evaluate both CD4(+) and CD8(+) T-cell responses in MS and to make both subsets a consideration in the development of novel therapeutic strategies.

Identification of the molecular chaperone alpha B-crystallin in demineralized bone powder and osteoblast-like cells

Bone is subjected to a variety of physiological, as well as cell-deforming biomechanical stresses, including hydrostatic compression and fluid flow. However, little is known about the molecular mechanisms that protect bone cells from mechanical, ischemic, or oxidative damage. Crystallins are 20 kD heat shock proteins that function as molecular chaperones. We tested the hypothesis that alpha B-crystallin (alphaB-crystallin), the most widely expressed vertebrate crystallin, is present in bone and osteoblast-like cells. Noncollagenous proteins (NCPs) were extracted from human demineralized bone matrix with 4 M guanidine HCI containing 0.5 M CaCl2 and protease inhibitors, defatted, dialyzed against 0.2% (v/v) Triton X-100 in 100 mM Tris-HCI (pH 7.2) and water, centrifuged, and lyophilized. The NCPs were separated by 2D IEF/SDS-PAGE. The two most abundant 20 kD spots, with apparent pIs of 7.85 and 7.42 in urea gels, were excised, subjected to matrix-assisted laser desorption ionization/time-of-flight mass spectrometry, and identified as alphaB-crystallins. Indirect immunofluorescence localized alphaB-crystallin to the interphase nucleus, cytoskeleton and cytoplasm of proliferating MC3T3-E1 mouse osteoblast-like cells, as well as the cytoskeleton and cytoplasm of confluent cells. In conclusion, alphaB-crystallin is present in bone and osteoblast-like cells. We hypothesize that alphaB-crystallin may play a role in protecting the osteoblast cytoskeleton from mechanical stress and may be important in modulating nuclear or cellular functions, such as transcription or apoptosis, as observed in other tissues.

Analysis of crystallin-crystallin interactions by surface plasmon resonance

The mechanism of aggregation and insolubilization of lens proteins was examined based on the kinetics of crystallin-crystallin interaction determined by the surface plasmon resonance method on a BlAcore system. Lens proteins are composed mainly of three types crystallins, alpha-, beta-, and gamma-crystallin. The present study indicated that alpha-crystallin shows marked self-interaction. Furthermore, this interaction was shown to be due to alphaA-crystallin, which is a subunit of alpha-crystallin. It was also clarified that this mutual interaction of aA-crystallin decreases abruptly after the age of 20 years. On the other hand, it was assumed that alphaB-crystallin, the other subunit of alpha-crystallin, may play an important role in interactions with beta- and gamma-crystallin, while a-crystallin shows chaperone-like activity. Based on the present results, alphaA- and betaB-crystallin may play different roles when alpha-crystallin displays chaperone-like activity, and also that the decreased chaperone-like activity of a-crystallin may finally result in cataract formation following aggregation and insolubilization of lens proteins.

D-amino acids in living higher organisms

The homochirality of biological amino acids (L-amino acids) and of the RNA/DNA backbone (D-ribose) might have become established before the origin of life. It has been considered that D-amino acids and L-sugars were eliminated on the primitive Earth. Therefore, the presence and function of D-amino acids in living organisms have not been studied except for D-amino acids in the cell walls of microorganisms. However, D-amino acids were recently found in various living higher organisms in the form of free amino acids, peptides, and proteins. Free D-aspartate and D-serine are present and may have important physiological functions in mammals. D-amino acids in peptides are well known as opioid peptides and neuropeptides. In protein, D-aspartate residues increase during aging. This review deals with recent advances in the study of D-amino acids in higher organisms.

Familial cardioneuromyopathy with hyaline masses and nemaline rods: a novel phenotype

Two siblings (patients 1 and 2) had adult-onset muscle weakness that was greater distally than proximally, as well as respiratory insufficiency, cardiomyopathy, and cervical spine anomalies. Electromyography studies indicated myopathy and findings consistent with neuropathy in both. In the deltoid muscle of patient 1 and the anterior tibial muscle of patient 2, myriad type 1 fibers harbored large, irregularly polygonal, and mostly central hyaline masses, small vacuoles, and nemaline rods flanking the hyaline masses or congregated under the sarcolemma. The hyaline masses are intensely congophilic; react strongly for desmin, alphaB-crystallin, alpha1-antichymotrypsin, and ubiquitin and variably for gelsolin and dystrophin; and are devoid of alpha-actinin, nebulin, titin, and slow myosin. The presence of ubiquitin, gelsolin, and fragmented filaments, and the absence of nebulin, titin, alpha-actinin, and slow myosin in the hyaline masses, signal nonlysosomal protein degradation. Ultrastructurally, the hyaline masses are composed of intermediate-density amorphous material intermingled with fragmented filaments and irregularly branching, pleomorphic, highly electron-dense material, resembling the hyaline structures of myofibrillar myopathy. We conclude that the pathological process in this syndrome is one that induces destruction of myofibrillar components, resulting in aggregation of the degraded residues in hyaline masses, and causes replication of Z disks, resulting in formation of nemaline rods.

Correlation between the loss of the chaperone-like activity and the oxidation, isomerization and racemization of gamma-irradiated alpha-crystallin

Alpha-crystallin possesses a molecular chaperone-like activity that prevents proteins from aggregating; however, the mechanism of this activity is not well known. Here we have taken gamma-irradiated alpha-crystallin and studied the relationship between the decrease in chaperone-like activity and the modifications such as oxidation, isomerization and racemization of amino acids in this molecule. We found that the chaperone-like activity of alpha-crystallin decreased with increasing gamma irradiation. After 4000 Gy gamma irradiation the activity of alpha-crystallin was reduced to 40% of the level of nonirradiated, native alpha-crystallin. The circular dichroism spectrum showed that the secondary structure of the irradiated alpha-crystallin had not changed. However, its tertiary structure appeared to change following more than 1000 Gy irradiation. Sodium dodecyl sulfatepolyacrylamide gel electrophoresis also indicated that cross-linking of alpha-crystallin increased with increasing radiation doses. Irradiated and nonirradiated alpha-crystallin was subjected to trypsin digestion and peptide analysis by reverse-phase high-performance liquid chromatography and mass and sequence analysis. Depending on the radiation dose, Met-1 of alpha A-crystallin was oxidized to methionine sulfoxide. In addition, Asp-151 of alpha A-crystallin was isomerized to the beta-Asp form after irradiation, and racemization of Asp-151 decreased. Thus, the loss of the chaperone-like activity of alpha-crystallin is related to changes in its isomerization, oxidation and racemization.

The major in vivo modifications of the human water-insoluble lens crystallins are disulfide bonds, deamidation, methionine oxidation and backbone cleavage

This investigation of the water-insoluble crystallins from human lenses has used multiple chromatographic separations to obtain proteins of sufficient purity for mass spectrometric analysis. Each fraction was analysed to determine the molecular masses of the constituent proteins as well as peptides in tryptic digests of these proteins. The major components of the water-insoluble crystallins were identified as alphaA- and alphaB-crystallins. In addition, gammaS-, betaB1-, gammaD-, betaA3/A1- and betaB2-crystallins were found, in order of decreasing abundance. Although there was evidence of some backbone cleavage, the predominant forms of alphaA-, alphaB, betaB2-, gammaS- and gammaD-crystallins were the intact polypeptide chains. The major modifications distinguishing the water-soluble crystallins were increased disulfide bonding, oxidation of Met, deamidation of Gln and Asn and backbone cleavage. Of the many reactions hypothesized to lead to crystallin insolubility and cataract, these results most strongly support metal-catalysed oxidation, deamidation and truncation as initiators of conformational changes that favor aggregation.

Canonical heat shock element in the alpha B-crystallin gene shows tissue-specific and developmentally controlled interactions with heat shock factor

Oligomerization of the heat shock factor (HSF) and its interaction with the heat shock element (HSE) are the hallmark of active transcriptional response to tangible physical or chemical stress. It is unknown if these interactions are subject to control and modulation by developmental cues and thus have tissue or stage specificity. By using promoter sequences containing a canonical HSE from the alphaB-crystallin gene, we demonstrate a tissue-specific transition from monomeric (in fetal and early neonatal stages that lack oligomeric HSF.HSE complexes) to oligomeric HSF-HSE interactions by postnatal day 10-21 in the ocular lens. Developmental control of these interactions is further demonstrated by induction of oligomeric HSF.HSE complexes in neonatal extracts by in vitro manipulations, interestingly, only in the lens and not in the brain, heart, or liver extracts. The exclusive presence of oligomeric HSF.HSE complexes in the postnatal/adult lens corresponds to known highly increased number of alphaB-crystallin transcripts in this tissue.