Mammalian Small Heat Shock Proteins Research Articles

A comprehensive review of the interaction between COVID-19 spike proteins with mammalian small and major heat shock proteins.

Coronavirus disease 2019 (COVID-19) is a novel disease that had devastating effects on human lives and the country's economies worldwide. This disease shows similar parasitic traits, requiring the host's biomolecules for its survival and propagation. Spike glycoproteins severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 spike protein) located on the surface of the COVID-19 virus serve as a potential hotspot for antiviral drug development based on their structure. COVID-19 virus calls into action the chaperonin system that assists the attacker, hence favoring infection. To investigate the interaction that occurs between SARS-CoV-2 spike protein and human molecular chaperons (HSPA8 and sHSP27), a series of steps were carried out which included sequence attainment and analysis, followed by multiple sequence alignment, homology modeling, and protein-protein docking which we performed using Cluspro to predict the interactions between SARS-CoV-2 spike protein and human molecular chaperones of interest. Our findings depicted that SARS-CoV-2 spike protein consists of three distinct chains, chains A, B, and C, which interact forming hydrogen bonds, hydrophobic interactions, and electrostatic interactions with both human HSPA8 and HSP27 with -828.3 and -827.9 kcal/mol as binding energies for human HSPA8 and -1166.7 and -1165.9 kcal/mol for HSP27.

Functional Diversity of Mammalian Small Heat Shock Proteins: A Review.

The small heat shock proteins (sHSPs), whose molecular weight ranges from 12∼43 kDa, are members of the heat shock protein (HSP) family that are widely found in all organisms. As intracellular stress resistance molecules, sHSPs play an important role in maintaining the homeostasis of the intracellular environment under various stressful conditions. A total of 10 sHSPs have been identified in mammals, sharing conserved α-crystal domains combined with variable N-terminal and C-terminal regions. Unlike large-molecular-weight HSP, sHSPs prevent substrate protein aggregation through an ATP-independent mechanism. In addition to chaperone activity, sHSPs were also shown to suppress apoptosis, ferroptosis, and senescence, promote autophagy, regulate cytoskeletal dynamics, maintain membrane stability, control the direction of cellular differentiation, modulate angiogenesis, and spermatogenesis, as well as attenuate the inflammatory response and reduce oxidative damage. Phosphorylation is the most significant post-translational modification of sHSPs and is usually an indicator of their activation. Furthermore, abnormalities in sHSPs often lead to aggregation of substrate proteins and dysfunction of client proteins, resulting in disease. This paper reviews the various biological functions of sHSPs in mammals, emphasizing the roles of different sHSPs in specific cellular activities. In addition, we discuss the effect of phosphorylation on the function of sHSPs and the association between sHSPs and disease.

Elucidation of Diverse Physico-Chemical Parameters in Mammalian Small Heat Shock Proteins: A Comprehensive Classification and Structural and Functional Exploration Using In Silico Approach.

Small heat shock proteins (sHSPs), often known as molecular chaperones, are most prevalent in nature. Under certain stress-induced conditions, these sHSPs act as an ATP-independent variation and thus prevent the inactivation of various non-native substrate proteins and their aggregation. They also assist other ATP-dependent chaperones in the refolding of these substrates. In the case of prokaryotes and lower eukaryotes, the chaperone functions of sHSPs can bind a wide range of cellular proteins but preferentially protect translation-related proteins and metabolic enzymes. Eukaryotes usually encode a larger number of sHSPs than those of prokaryotes. The chaperone functions of mammalian sHSPs are regulated by phosphorylation in cells and also by temperature. Their sHSPs have different sub-cellular compartments and cell/tissue specificity. The substrate proteins of mammalian sHSPs or eukaryotic sHSPs accordingly reflect their multi-cellular complexity. The sHSPs of animals play roles in different physiological processes as cell differentiation, apoptosis, and longevity. In this work, the characterization, location, tissue specificity, and functional diversity of sHSPs from seven different mammalian species with special emphasis on humans have been studied. Through this extensive work, a novel and significant attempt have been made to classify them based on their omnipresence, tissue specificity, localization, secondary structure, probable mutations, and evolutionary significance.

The functional roles of the unstructured N- and C-terminal regions in αB-crystallin and other mammalian small heat-shock proteins.

Small heat-shock proteins (sHsps), such as αB-crystallin, are one of the major classes of molecular chaperone proteins. In vivo, under conditions of cellular stress, sHsps are the principal defence proteins that prevent large-scale protein aggregation. Progress in determining the structure of sHsps has been significant recently, particularly in relation to the conserved, central and β-sheet structured α-crystallin domain (ACD). However, an understanding of the structure and functional roles of the N- and C-terminal flanking regions has proved elusive mainly because of their unstructured and dynamic nature. In this paper, we propose functional roles for both flanking regions, based around three properties: (i) they act in a localised crowding manner to regulate interactions with target proteins during chaperone action, (ii) they protect the ACD from deleterious amyloid fibril formation and (iii) the flexibility of these regions, particularly at the extreme C-terminus in mammalian sHsps, provides solubility for sHsps under chaperone and non-chaperone conditions. In the eye lens, these properties are highly relevant as the crystallin proteins, in particular the two sHsps αA- and αB-crystallin, are present at very high concentrations.

An interaction study in mammalian cells demonstrates weak binding of HSPB2 to BAG3, which is regulated by HSPB3 and abrogated by HSPB8.

The ten mammalian small heat shock proteins (sHSPs/HSPBs) show a different expression profile, although the majority of them are abundant in skeletal and cardiac muscles. HSPBs form hetero-oligomers and homo-oligomers by interacting together and complexes containing, e.g., HSPB2/HSPB3 or HSPB1/HSPB5 have been documented in mammalian cells and muscles. Moreover, HSPB8 associates with the Hsc70/Hsp70 co-chaperone BAG3, in mammalian, skeletal, and cardiac muscle cells. Interaction of HSPB8 with BAG3 regulates its stability and function. Weak association of HSPB5 and HSPB6 with BAG3 has been also reported upon overexpression in cells, supporting the idea that BAG3 might indirectly modulate the function of several HSPBs. However, it is yet unknown whether other HSPBs highly expressed in muscles such as HSPB2 and HSPB3 also bind to BAG3. Here, we report that in mammalian cells, upon overexpression, HSPB2 binds to BAG3 with an affinity weaker than HSPB8. HSPB2 competes with HSPB8 for binding to BAG3. In contrast, HSPB3 negatively regulates HSPB2 association with BAG3. In human myoblasts that express HSPB2, HSPB3, HSPB8, and BAG3, the latter interacts selectively with HSPB8. Combining these data, it supports the interpretation that HSPB8-BAG3 is the preferred interaction.

Species-Specific Structural and Functional Divergence of α-Crystallins: Zebrafish αBa- and Rodent αA(ins)-Crystallin Encode Activated Chaperones.

In addition to contributing to lens optical properties, the α-crystallins are small heat shock proteins that possess chaperone activity and are predicted to bind and sequester destabilized proteins to delay cataract formation. The current model of α-crystallin chaperone mechanism envisions a transition from the native oligomer to an activated form that has higher affinity to non-native states of the substrate. Previous studies have suggested that this oligomeric plasticity is encoded in the primary sequence and controls access to high affinity binding sites within the N-terminal domain. Here, we further examined the role of sequence variation in the context of species-specific α-crystallins from rat and zebrafish. Alternative splicing of the αA gene in rodents produces αA(ins), which is distinguished by a longer N-terminal domain. The zebrafish genome includes duplicate αB-crystallin genes, αBa and αBb, which display divergent primary sequence and tissue expression patterns. Equilibrium binding experiments were employed to quantitatively define chaperone interactions with a destabilized model substrate, T4 lysozyme. In combination with multiangle light scattering, we show that rat αA(ins) and zebrafish α-crystallins display distinct global structural properties and chaperone activities. Notably, we find that αA(ins) and αBa demonstrate substantially enhanced chaperone function relative to other α-crystallins, binding the same substrate more than 2 orders of magnitude higher affinity and mimicking the activity of fully activated mammalian small heat shock proteins. These results emphasize the role of sequence divergence as an evolutionary strategy to tune chaperone function to the requirements of the tissues and organisms in which they are expressed.

A yeast two-hybrid screen reveals a strong interaction between the Legionella chaperonin Hsp60 and the host cell small heat shock protein Hsp10.

L. pneumophila is an intracellular bacterium that replicates inside a membrane-bound vacuole called Legionella-containing vacuole (LCV), where it plentifully liberates its HtpB chaperonin. From LCV, HtpB reaches the host cell cytoplasm, where it interacts with SAMDC, a cytoplasmic protein required for synthesis of host polyamines that are important for intracellular growth of L. pneumophila. Additionally, cytoplasmic expression of HtpB in S. cerevisiae induces pseudohyphal growth, and in mammalian cells recruits mitochondria to LCV, and modifies actin microfilaments organization. This led us to hypothesize here that HtpB recruits a protein(s) from eukaryotic cells that is involved in the emergence of the aforementioned phenotypes. To identify this protein, a commercially available HeLa cDNA library was screened using a yeast two-hybrid system. Approximately 5×10(6) yeast clones carrying HeLa cDNA library plasmid were screened. Twenty-one positive clones were identified. DNA sequence analysis revealed that all of these positive clones encoded the mammalian small heat shock protein Hsp10. Based on the fact that chaperonions are required to interact with co-chaperonins to function properly in protein folding, we believe that HtpB recruits the host cell Hsp10 to appropriately interact with SAMDC and to induce the multifunction phenotypes deemed important in L. pneumophila pathogenesis.

Phosphomimics Destabilize Hsp27 Oligomeric Assemblies and Enhance Chaperone Activity

Serine phosphorylation of the mammalian small heat-shock protein Hsp27 at residues 15, 78, and 82 is thought to regulate its structure and chaperone function; however, the site-specific impact has not been established. We used mass spectrometry to assess the combinatorial effect of mutations that mimic phosphorylation upon the oligomeric state of Hsp27. Comprehensive dimerization yielded a relatively uncrowded spectrum, composed solely of even-sized oligomers. Modification at one or two serines decreased the average oligomeric size, while the triple mutant was predominantly a dimer. These changes were reflected in a greater propensity for oligomers to dissociate upon increased modification. The ability of Hsp27 to prevent amorphous or fibrillar aggregation of target proteins was enhanced and correlated with the amount of dissociated species present. We propose that, in vivo, phosphorylation promotes oligomer dissociation, thereby enhancing chaperone activity. Our data support a model in which dimers are the chaperone-active component of Hsp27.

Different anti-aggregation and pro-degradative functions of the members of the mammalian sHSP family in neurological disorders

The family of the mammalian small heat-shock proteins consists of 10 members (sHSPs/HSPBs: HSPB1-HSPB10) that all share a highly conserved C-terminal alpha-crystallin domain, important for the modulation of both their structural and functional properties. HSPB proteins are biochemically classified as molecular chaperones and participate in protein quality control, preventing the aggregation of unfolded or misfolded proteins and/or assisting in their degradation. Thus, several members of the HSPB family have been suggested to be protective in a number of neurodegenerative and neuromuscular diseases that are characterized by protein misfolding. However, the pro-refolding, anti-aggregation or pro-degradative properties of the various members of the HSPB family differ largely, thereby influencing their efficacy and protective functions. Such diversity depends on several factors, including biochemical and physical properties of the unfolded/misfolded client, the expression levels and the subcellular localization of both the chaperone and the client proteins. Furthermore, although some HSPB members are inefficient at inhibiting protein aggregation, they can still exert neuroprotective effects by other, as yet unidentified, manners; e.g. by maintaining the proper cellular redox state or/and by preventing the activation of the apoptotic cascade. Here, we will focus our attention on how the differences in the activities of the HSPB proteins can influence neurodegenerative and neuromuscular disorders characterized by accumulation of aggregate-prone proteins. Understanding their mechanism of action may allow us to target a specific member in a specific cell type/disease for therapeutic purposes.

Structural and Functional Aspects of Hetero-oligomers Formed by the Small Heat Shock Proteins αB-Crystallin and HSP27

αB-crystallin and HSP27 are mammalian intracellular small heat shock proteins. These proteins exchange subunits in a rapid and temperature-dependent manner. This facile subunit exchange suggests that differential expression could be used by the cell to regulate the response to stress. A robust technique defines parameters for the dynamic interaction between the major mammalian small heat shock proteins. Small heat shock proteins (sHSPs) exist as large polydisperse species in which there is constant dynamic subunit exchange between oligomeric and dissociated forms. Their primary role in vivo is to bind destabilized proteins and prevent their misfolding and aggregation. αB-Crystallin (αB) and HSP27 are the two most widely distributed and most studied sHSPs in the human body. They are coexpressed in different tissues, where they are known to associate with each other to form hetero-oligomeric complexes. In this study, we aimed to determine how these two sHSPs interact to form hetero-oligomers in vitro and whether, by doing so, there is an increase in their chaperone activity and stability compared with their homo-oligomeric forms. Our results demonstrate that HSP27 and αB formed polydisperse hetero-oligomers in vitro, which had an average molecular mass that was intermediate of each of the homo-oligomers and which were more thermostable than αB, but less so than HSP27. The hetero-oligomer chaperone function was found to be equivalent to that of αB, with each being significantly better in preventing the amorphous aggregation of α-lactalbumin and the amyloid fibril formation of α-synuclein in comparison with HSP27. Using mass spectrometry to monitor subunit exchange over time, we found that HSP27 and αB exchanged subunits 23% faster than the reported rate for HSP27 and αA and almost twice that for αA and αB. This represents the first quantitative evaluation of αB/HSP27 subunit exchange, and the results are discussed in the broader context of regulation of function and cellular proteostasis.

The family of mammalian small heat shock proteins (HSPBs): Implications in protein deposit diseases and motor neuropathies

A number of neurological and muscular disorders are characterized by the accumulation of aggregate-prone proteins and are referred to as protein deposit or protein conformation diseases. Besides some sporadic forms, most of them are genetically inherited in an autosomal dominant manner, although recessive forms also exist. Although genetically very heterogeneous, some of these diseases are the result of mutations in some members of the mammalian small heat shock protein family (sHSP/HSPB), which are key players of the protein quality control system and participate, together with other molecular chaperones and co-chaperones, in the maintenance of protein homeostasis. Thus, on one hand upregulation of specific members of the HSPB family can exert protective effects in protein deposit diseases, such as the polyglutamine diseases. On the other hand, mutations in the HSPBs lead to neurological and muscular disorders, which may be due to a loss-of-function in protein quality control and/or to a gain-of-toxic function, resulting from the aggregation-proneness of the mutants. In this review we summarize the current knowledge about some of the best characterized functions of the HSPBs (e.g. role in cytoskeleton stabilization, chaperone function, anti-aggregation and anti-apoptotic activities), also highlighting differences in the properties of the various HSPBs and how these may counteract protein aggregation diseases. We also describe the mutations in the various HSPBs associated with neurological and muscular disorders and we discuss how gain-of-toxic function mechanisms (e.g. due to the mutated HSPB protein instability and aggregation) and/or loss-of-function mechanisms can contribute to HSPB-associated pathologies. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Study ofαB-Crystallin Expression in Gerbil BCAO Model of Transient Global Cerebral Ischemia

αB-crystallin (α-BC), the fifth member of mammalian small heat shock protein family (HspB5), is known to be expressed in many tissues and has a distinctive interaction with cytoskeleton components. In this study, we investigated that α-BC and microtubule-associated protein-2 (MAP-2), a neuron-specific cytoskeleton protein, were coexpressed in neurons of Gerbil cortex, while in subcortex Gerbil brains, we found that several MAP-2-negative glia cells also express α-BC. When subjected to 10-minute bilateral carotid artery occlusion (BCAO), an increment was observed in α-BC-positive cells after 6-hour reperfusion and peaked at around 7 days after. In the same circumstances, the number and the staining concentration of MAP-2 positive neurons significantly decreased immediately after 6-hour reperfusion, followed by a slow recovery, which is consistent with the increase of α-BC. Our results suggested that α-BC plays an important role in brain ischemia, providing the early protection of neurons by giving intracellular supports through the maintenance of cytoskeleton and extracellular supports through the protection of glia cells.

The Small Heat-Shock Proteins HSPB2 and HSPB3 Form Well-defined Heterooligomers in a Unique 3 to 1 Subunit Ratio

Various mammalian small heat-shock proteins (sHSPs) can interact with one another to form large polydisperse assemblies. In muscle cells, HSPB2/MKBP (myotonic dystrophy protein kinase-binding protein) and HSPB3 have been shown to form an independent complex. To date, the biochemical properties of this complex have not been thoroughly characterized. In this study, we show that recombinant HSPB2 and HSPB3 can be successfully purified from Escherichia coli cells co-expressing both proteins. Nanoelectrospray ionization mass spectrometry and sedimentation velocity analytical ultracentrifugation analysis showed that HSPB2/B3 forms a series of well defined hetero-oligomers, consisting of 4, 8, 12, 16, 20 and 24 subunits, each maintaining a strict 3:1 HSPB2/HSPB3 subunit ratio. These complexes are thermally stable up to 40 °C, as determined by far-UV circular dichroism spectroscopy. Surprisingly, HSPB2/B3 exerted a poor chaperone-like and thermoprotective activity, which is likely related to the low surface hydrophobicity, as revealed by its interaction with the hydrophobic probe 1-anilino-8-naphthalenesulfonic acid. Co-immunoprecipitation experiments demonstrated that the HSPB2/B3 oligomer cannot interact with HSP20, HSP27 or αB-crystallin, whereas the homomeric form of HSPB2, thus not in complex with HSPB3, could associate efficiently with HSP20. Taken altogether, this study provides evidence that, despite the high level of sequence homology within the sHSP family the biochemical properties of the HSPB2/B3 complex are distinctly different from those of other sHSPs, indicating that the HSPB2/B3 assembly is likely to possess cellular functions other than those of its family members.

HspB5/αB-Crystallin: Properties and Current Progress in Neuropathy

HspB5/alphaB-crystallin (alphaBC), one of the most representative member of mammalian small heat shock protein family (sHsp), shares the common features with other nine members HspB1-B4 and HspB6-10. Meanwhile, it has a strong antiapoptic effect; its interaction with cytoskeleton participates in maintaining cell structure and plays an important role in cytoprotection. Recent studies reveal that HspB5 has a strong relationship with neurological diseases acting as a protective molecular chaperone or in certain conditions, a pathogenic factor. This review gives a brief introduction on properties of HspB5, its current progress in neurological diseases and potential therapeutic intervention in demyelinating disease, neurodegenerative disease, myopathy and cerebrovascular disease.

Insights into function and regulation of small heat shock protein 25 (HSPB1) in a mouse model with targeted gene disruption

The mammalian small heat shock protein (sHSPs) family is comprised of 10 members and includes HSPB1, which is proposed to play an essential role in cellular physiology, acting as a molecular chaperone to regulate diverse cellular processes. Whilst differential roles for sHSPs are suggested for specific tissues, the relative contribution of individual sHSP family members in cellular and organ physiology remains unclear. To address the function of HSPB1 in vivo and determine its tissue-specific expression during development and in the adult, we generated knock-in mice where the coding sequence of hspb1 is replaced by a lacZ reporter gene. Hspb1 expression marks myogenic differentiation with specific expression first confined to developing cardiac muscles and the vascular system, and later in skeletal muscles with specific expression at advanced stages of myoblast differentiation. In the adult, hspb1 expression was observed in other tissues, such as stratified squamous epithelium of skin, oronasal cavity, tongue, esophagus, and uterine cervix but its expression was most prominent in the musculature. Interestingly, in cardiac muscle hsbp1 expression was down-regulated during the neonatal period and maintained to a relatively low steady-level throughout adulthood. Despite this widespread expression, hspb1-/- mice were viable and fertile with no apparent morphological abnormalities in tissues under physiological conditions. However, at the cellular level and under stress conditions (heat challenge), HSPB1 act synergistically with the stress-induced HSPA1 (HSP70) in thermotolerance development, protecting cells from apoptosis. Our data thus indicate a nonessential role for HSPB1 in embryonic development and for maintenance of tissues under physiological conditions, but also shows that it plays an important role by acting synergistically with other HSPs during stress conditions to exert cytoprotection and anti-apoptotic effects.

Recruitment of phosphorylated small heat shock protein Hsp27 to nuclear speckles without stress

During stress, the mammalian small heat shock protein Hsp27 enters cell nuclei. The present study examines the requirements for entry of Hsp27 into nuclei of normal rat kidney (NRK) renal epithelial cells, and for its interactions with specific nuclear structures. We find that phosphorylation of Hsp27 is necessary for the efficient entry into nuclei during heat shock but not sufficient for efficient nuclear entry under control conditions. We further report that Hsp27 is recruited to an RNAse sensitive fraction of SC35 positive nuclear speckles, but not other intranuclear structures, in response to heat shock. Intriguingly, Hsp27 phosphorylation, in the absence of stress, is sufficient for recruitment to speckles found in post-anaphase stage mitotic cells. Additionally, pseudophosphorylated Hsp27 fused to a nuclear localization peptide (NLS) is recruited to nuclear speckles in unstressed interphase cells, but wildtype and nonphosphorylatable Hsp27 NLS fusion proteins are not. The expression of NLS-Hsp27 mutants does not enhance colony forming abilities of cells subjected to severe heat shock, but does regulate nuclear speckle morphology. These data demonstrate that phosphorylation, but not stress, mediates Hsp27 recruitment to an RNAse soluble fraction of nuclear speckles and support a site-specific role for Hsp27 within the nucleus.

Conformational changes resulting from pseudophosphorylation of mammalian small heat shock proteins—a two-hybrid study

The human genome codes for 10 so-called mammalian small heat shock or stress proteins (sHsp) with the various tissues expressing characteristic sets of sHsps. Most sHsps interact with each other and form homo- and heterooligomeric complexes. Some of the sHsps are phosphoproteins in vivo, and phosphorylation has been implicated in the regulation of complex size and composition. In this study, we analyze, by the 2-hybrid method, the reporter gene activation pattern of several sHsp pairs that previously have been demonstrated to interact. We show that pseudophosphorylation (mimicry of phosphorylation) of the homologous phosphorylation sites Ser15 and Ser16 in Hsp27 and Hsp20, respectively, modulates characteristics of these sHsps that can be detected by their ability to activate reporter genes in suitable 2-hybrid assays. Pseudophosphorylation of the separated N-terminus of Hsp27 alone is not sufficient for the activation of the reporter genes, whereas the separated C-terminus is sufficient. We conclude that pseudophosphorylation of Hsp27 and Hsp20 at their N-termini results in conformational changes that can be detected by their interaction with other sHsps. Pseudophosphorylation of alphaB-crystallin at Ser19, in contrast, had no detectable consequences.

Developmentally regulated gene expression of the small heat shock protein Hsp27 in zebrafish embryos

Mammalian small heat shock proteins including Hsp27 and alpha-B crystallin are constitutively expressed in various adult and embryonic tissues including skeletal and cardiac muscle. However, the function of these proteins during embryonic development is not understood, and information on their expression during the earliest stages of development is limited. We have recently demonstrated constitutive and stress inducible expression of a homologue of human Hsp27 in adult zebrafish, an important experimental model of vertebrate developmental processes. Here, we assessed the temporospatial dynamics of zebrafish Hsp27 ( hsp27) and alpha-B crystallin ( cryab) gene expression using reverse-transcriptase PCR (RT–PCR) and hsp27 expression by in situ hybridization. Our results reveal that initial upregulation of hsp27 expression occurs during early gastrulation. Expression of hsp27 is detected transiently in developing myotomes, lens and brain, and more persistently in developing heart. The constitutive expression level of hsp27 in embryos at some stages of development is considerably greater than that observed in unstressed adult tissues. Expression of hsp27 was also observed in all tissues examined in embryos recovering from heat stress. The pattern of expression observed for hsp27 overlaps partially, but not completely, with that reported for other heat shock proteins.

Interactions of HSP22 (HSPB8) with HSP20, αB-crystallin, and HSPB3

Seven of the 10 mammalian small heat shock proteins (sHSP) are expressed in muscle where they constitute 3% or more of total protein. sHSPs interact with one another, and these interactions are believed to be important for their functions. In cell types expressing multiple sHSPs, it is of interest to know which sHSPs interact with one another. We have previously shown that HSP22 interacts with itself as well as with HSP27, MKBP, and cvHSP. Using yeast two-hybrid assays and Förster resonance energy transfer microscopy, we now show that HSP22 also can interact with two additional members of the sHSP family, αB-crystallin and HSP20. We also show that HSP22 is found in HPLC fractions of primate cardiac muscle containing high molecular weight complexes that include αB-crystallin and HSP20. Our results suggest that a variety of oligomers composed of different proportions of different sHSPs may form in cell types expressing multiple sHSPs.

Recombinant human αA-crystallin can protect the enzymatic activity of CpUDG against thermal inactivation

α-Crystallin is one of the major protein components in mammalian lens fiber cells. It is composed of αA and αB subunits that have structural homology to the family of mammalian small heat shock proteins. Horwitz firstly characterized native α-crystallin as a molecular chaperone in vitro based on its ability to prevent heat-induced aggregation of lens proteins and enzymes. Andley et al. cloned and expressed human αA-crystallin in Escherichia coli and confirmed its chaperone activity by suppression of thermal aggregation and singlet oxygen-induced opacification. Although αA-crystallin acts as a chaperone protein, there is no report showing on its ability to protect enzymes against thermal inactivation. Here, we present data showing that αA-crystallin can prevent thermal inactivation of CpUDG that catalyzes uracil removal from DNAs.