α-Crystallins are small heat shock proteins: Functional and structural properties

Anti-aggregation Properties of the Mini-Peptides Derived from Alpha Crystallin Domain of the Small Heat Shock Protein, Tpv HSP 14.3

The highly conserved alpha crystallin domain of the small heat shock proteins is essential for dimerization and also implicated in substrate interaction. In this study, we designed four novel mini-peptides from alpha crystallin domain of archaeal Small Heat Shock Protein Tpv HSP 14.3. Among the peptide designs, the mini-peptides 38SDLVLEAEMAGFDKKNIKVS57 and 40LVLEAEMAGFD50 overlapped to the sequences of β3-β4 region. The other two peptides 77YIDQRVDKVYKVVKLPVE94 and 107GILTVRMK114 correspond to β6-β7 region and β9, respectively. Functional activity of the peptides was evaluated by monitoring heat-induced aggregation of the model substrates alcohol dehydrogenase at 43 °C and citrate synthase at 45 °C. Our results showed that the (38-57) and the (77-94) fragments exhibited chaperone activity with both of the substrate proteins. The (40-50) fragment while exhibiting a noticeable protective effect (> 90%) when tested with citrate synthase showed an anti-chaperone property toward alcohol dehydrogenase. Unlike the (40-50) fragment, the (107-114) fragment did not show any chaperone activity with citrate synthase but exhibited the highest chaperone efficiency among four mini-peptides with alcohol dehydrogenase. The selectivity of the (40-50) and the (107-114) fragments in targeting the client proteins is most likely dependent on their surface hydrophobicity and/or charge as revealed by the sequence and exposed surface analyses.

Constitutively expressed small heat shock protein LsHsp21.5 not only enhances heat tolerance but also helps to maintain reproduction in female Laodelphax striatellus

Coping with stressful conditions and maintaining reproduction are two key biological processes that affect insect population dynamics. Small heat shock proteins (sHSPs) are involved in the stress response and the development of insects. The sHsp gene Laodelphax striatellus (Hemiptera: Delphacidae) sHsp 21.5 (LsHsp21.5) showed constitutive, stage- and organ-specific expression in L. striatellus, a pest that damages cultivated rice in east Asia. The expression of LsHsp21.5 was highest in the ovary, with 43.60, 12.99 and 1.45 time higher expression here than in the head, gut and female fat bodies, respectively. The expression of this gene was weakly affected by heat or cold shock. The gene provided in vitro protection against heat damage to malate dehydrogenase and in vivo protection against heat stress in Escherichia coli (Enterobacteriales: Enterobacteriaceae) BL21(DE3) and L. striatellus. Moreover, L. striatellus reproduction decreased by 1.85 times when the expression of LsHsp21.5 was inhibited by RNA interference. The expression of some genes related to reproduction, such as the homologous gene of chorion protein, also declined. These results suggest that LsHsp21.5 expression not only protects other proteins against stress but also helps maintain the stable expression of some reproduction-related genes under non-stressful conditions, with impacts on L. striatellus fecundity.

Significant influence of four highly conserved amino-acids in lipochaperon-active sHsps on the structure and functions of the Lo18 protein

To cope with environmental stresses, bacteria have developed different strategies, including the production of small heat shock proteins (sHSP). All sHSPs are described for their role as molecular chaperones. Some of them, like the Lo18 protein synthesized by Oenococcus oeni, also have the particularity of acting as a lipochaperon to maintain membrane fluidity in its optimal state following cellular stresses. Lipochaperon activity is poorly characterized and very little information is available on the domains or amino-acids key to this activity. The aim in this paper is to investigate the importance at the protein structure and function level of four highly conserved residues in sHSP exhibiting lipochaperon activity. Thus, by combining in silico, in vitro and in vivo approaches the importance of three amino-acids present in the core of the protein was shown to maintain both the structure of Lo18 and its functions.

A review on oligomeric polydispersity and oligomers-dependent holding chaperone activity of the small heat-shock protein IbpB of Escherichia coli

Inclusion body-associated proteins IbpA and IbpB of MW 16 KDa are the two small heat-shock proteins (sHSPs) of Escherichia coli, and they have only holding, but not folding, chaperone activity. In vitro holdase activity of IbpB is more than that of IbpA, and in combination, they synergise. Both IbpA and IbpB monomers first form homodimers, which as building blocks subsequently oligomerize to make heavy oligomers with MW of MDa range; for IbpB, the MW range of heavy oligomers is 2.0-3.0 MDa, whereas for IbpA oligomers, the values in MDa are not so specified/reported. By temperature upshift, such large oligomers of IbpB, but not of IbpA, dissociate to make relatively small oligomeric assemblies of MW around 600-700KDa. The larger oligomers of IbpB are assumed to be inactive storage form, which on facing heat or oxidative stress dissociate into smaller oligomers of ATP-independent holding chaperone activity. These smaller oligomers bind with stress-induced partially denatured/unfolded and thereby going to be aggregated proteins, to give them protection against permanent damage and aggregation. On withdrawal of stress, IbpB transfers the bound substrate protein to the ATP-dependent bi-chaperone system DnaKJE-ClpB, having both holdase and foldase properties, to finally refold the protein. Of the two sHSPs IbpA and IbpB of E. coli, this review covers the recent advances in research on IbpB only.

Is the lipochaperone activity of sHSP a key to the stress response encoded in its primary sequence?

Several strategies have been put in place by organisms to adapt to their environment. One of these strategies is the production of stress proteins such as sHSPs, which have been widely described over the last 30 years for their role as molecular chaperones. Some sHSPs have, in addition, the particularity to exert a lipochaperone role by interacting with membrane lipids to maintain an optimal membrane fluidity. However, the mechanisms involved in this sHSP-lipid interaction remain poorly understood and described rather sporadically in the literature. This review gathers the information concerning the structure and function of these proteins available in the literature in order to highlight the mechanism involved in this interaction. In addition, analysis of primary sequence data of sHSPs available in database shows that sHSPs can interact with lipids via certain amino acid residues present on some β sheets of these proteins. These residues could have a key role in the structure and/or oligomerization dynamics of sHPSs, which is certainly essential for interaction with membrane lipids and consequently for maintaining optimal cell membrane fluidity.

Crystallin Alpha-B Overexpression as a Possible Marker of Reactive Astrogliosis in Human Cerebral Contusions

The pathophysiology of traumatic brain injury (TBI) has not yet been fully elucidated. Crystallin alpha-B (CRYAB) is a molecular chaperone that apparently tries to stabilize the rapid thickening of the intermediate filaments of glial fibrillary acidic protein (GFAP) during the process of reactive astrogliosis in response to TBI. Previous analyses of the gene expression profile in human brain contusion tissue showed us an exacerbated CRYAB overexpression. Here, we used 3, 3’-diaminobenzidine (DAB) immunohistochemistry and immunofluorescence to verify CRYAB overexpression and to describe its expression and distribution in samples of contused cortical tissue derived from emergency decompressive surgery after severe TBI. The histological expression of CRYAB was mainly seen in subcortical white matter astrocytes of injured tissue. Most of the cells that overexpressed GFAP in the analyzed tissue also overexpressed CRYAB, a finding corroborated by the co-localization of the two markers. The only difference was the presence of a few pyramidal neurons that expressed CRYAB in layer V of the cerebral cortex. The selective vulnerability of layer V of the cerebral cortex during TBI could explain the expression of CRYAB in neurons of this cortical layer. Our results indicate a parallel behavior in the cellular expression of CRYAB and GFAP during the subacute response to TBI. These results lead us to postulate CRYAB as a possible marker of reactive astrogliosis in contused cortical tissue.

Genome-wide identification and expression analysis of the Hsp gene superfamily in Asian long-horned beetle (Anoplophora glabripennis)

The environmental adaptability of insects has been a key focus of ecological research. As molecular chaperones, Heat shock proteins (Hsps) play an important role in insect responses to environmental stress. Anoplophora glabripennis is a destructive pest of broad-leaved trees such as poplars. The ability to adapt to low temperature is an important factor for successful colonization of A. glabripennis in new diffusion area. However, the roles of Hsp in the stress responses in A. glabripennis have not been established. In this study, we identified 47 Hsp genes, including 3 Hsp90, 14 Hsp70, 9 Hsp60, and 21 sHsp genes. The Hsp gene family expanded substantially in A. glabripennis. The differences in expression patterns may be related to the type and intensity of stress. Larval overwintering transcriptomes showed that 13 Hsp genes were not induced during overwintering and 21 Hsp genes were involved in the regulation of life activities under non-stress conditions. In a quantitative RT-PCR analysis, AglaHsp90-2 responded more quickly under gradient cooling treatments; AglaHsp90-2 and AglaHsp90-3 were sensitive to treatment at 0 °C for 6 h under instantaneous cooling. Our results provide a theoretical basis for clarifying the molecular mechanism of Hsp genes in A. glabripennis in responsing to environmental stresses.

Zeta-crystallin: a moonlighting player in cancer

Crystallins were firstly found as structural proteins of the eye lens. To this family belong proteins, such as ζ-crystallin, expressed ubiquitously, and endowed with enzyme activity. ζ-crystallin is a moonlighting protein endowed with two main different functions: (1) mRNA binding with stabilizing activity; (2) NADPH:quinone oxidoreductase. ζ-crystallin has been clearly demonstrated to stabilize mRNAs encoding proteins involved in renal glutamine catabolism during metabolic acidosis resulting in ammoniagenesis and bicarbonate ion production that concur to compensate such condition. ζ-crystallin binds also mRNAs encoding for antiapoptotic proteins, such as Bcl-2 in leukemia cells. On the other hand, the physiological role of its enzymatic activity is still elusive. Gathering research evidences and data mined from public databases, we provide a framework where all the known ζ-crystallin properties are called into question, making it a hypothetical pivotal player in cancer, allowing cells to hijack or subjugate the acidity response mechanism to increase their ability to resist oxidative stress and apoptosis, while fueling their glutamine addicted metabolism.

Molecular genetics of congenital cataracts

Congenital cataracts, the most common cause of visual impairment and blindness in children worldwide, have diverse etiologies. According to statistics analysis, about one quarter of congenital cataracts caused by genetic defects. Various mutations of more than one hundred genes have been identified in hereditary cataracts so far. In this review, we briefly summarize recent developments about the genetics, molecular mechanisms, and treatments of congenital cataracts. The studies of these pathogenic mutations and molecular genetics is making it possible for us to comprehend the underlying mechanisms of cataractogenesis and providing new insights into the preventive, diagnostic and therapeutic approaches of cataracts.

Small heat shock protein B3 (HSPB3) mutation in an axonal Charcot-Marie-Tooth disease family

Heat shock protein B3 (HSPB3) gene encodes a small heat-shock protein 27-like protein which has a high sequence homology with HSPB1. A mutation in the HSPB3 was reported as the putative underlying cause of distal hereditary motor neuropathy 2C (dHMN2C) in 2010. We identified a heterozygous mutation (c.352T>C, p.Tyr118His) in the HSPB3 from a Charcot-Marie-Tooth disease type 2 (CMT2) family by the method of targeted next generation sequencing. The mutation was located in the well conserved alpha-crystalline domain, and several in silico predictions indicated a pathogenic effect of the mutation. Clinical and electrophysiological features of the patients indicated the axonal type of CMT. Clinical symptoms without sensory involvements were similar between the present family and the previous family. Mutations in the HSPB1 and HSPB8 genes have been reported to be relevant with both types of CMT2 and dHMN. Our findings will help in the molecular diagnosis of CMT2 by expanding the phenotypic range due to the HSPB3 mutations.