Structural perturbation of α-crystallin and its chaperone-like activity

α-Crystallin is a multimeric lenticular protein that has recently been shown to be expressed in several non-lenticular tissues as well. It is shown to prevent aggregation of non-native proteins as a molecular chaperone. By using a non-thermal aggregation model, we could show that this process is temperature-dependent. We investigated the chaperone-like activity of α-crystallin towards photo-induced aggregation of γ-crystallin, aggregation of insulin and on the refolding induced aggregation of β- and γ-crystallins. We observed that α-crystallin could prevent photo-aggregation of γ-crystallin and this chaperone-like activity of α-crystallin is enhanced several fold at temperatures above 30°C. This enhancement parallels the exposure of its hydrophobic surfaces as a function of temperature, probed using hydrophobic fluorescent probes such as pyrene and 8-anilinonaphthalene-1-sulfonate. We, therefore, concluded that α-crystallin prevents the aggregation of other proteins by providing appropriately placed hydrophobic surfaces; a structural transition above 30°C involving enhanced or re-organized hydrophobic surfaces of α-crystallin is important for its chaperone-like activity. We also addressed the issue of conformational aspects of target proteins and found that their aggregation prone molten globule states bind to α-crystallin. We trace these developments and discuss some new lines that suggest the role of tertiary structural aspects in the chaperone process.     

Effects of temperature and concentration on bovine lens α-crystallin secondary structure: a circular dichroism spectroscopic study

Elucidation of the structure of α-crystallin, the major protein in all vertebrate lenses, is important for understanding its role in maintaining transparency and its function in other tissues under both normal and pathological conditions. Progress toward a unified consensus concerning the tertiary and quaternary structures of α-crystallin depends, in part, on an accurate estimation of its secondary structure. For the first time, three algorithms, SELCON, K2D and CONTIN were used to analyze far ultra-violet circular dichroism (UV–CD) spectra of bovine lens α-crystallin to estimate the secondary structure and to determine the effects of temperature and concentration. Under all experimental conditions tested, the analyses show that α-crystallin contains 14% α-helix, 35% β-sheet and the remainder, random coil and turns. The results suggest that α-crystallin is best classified as a mixed protein. In addition, increased temperature and concentration of α-crystallin result in increased α-helices with a compensatory decrease in β-sheets. Such structural alterations in α-crystallin may be functionally important during terminal differentiation of the lens fiber cells that is accompanied by increased protein concentrations and its role as a chaperone-like protein.     

Purification and characterisation of the cardenolide-specificβ-glucohydrolase CGH II from Digitalis lanata leaves

A cardenolide-hydrolysing β-D-glucosidase was isolated from young leaves of Digitalis lanata. Since this enzyme differs from the cardenolide glucohydrolase (CGH) described and characterised previously, it was termed cardenolide glucohydrolase II (CGH II). CGH II was detected in various Digitalis tissue cultures as well as in young leaves of D. lanata. The latter source was used as the starting material for the isolation and purification of CGH II. The specific enzyme activity reached about 15 pkat·mg^–1 protein in buffered leaf extracts. Optimal CGH II activity was seen at around pH 6.0 and 50 °C. CGH II was purified about 600-fold by anion exchange chromatography, size exclusion chromatography and hydroxyapatite chromatography. The apparent molecular mass of CGH II was 65 kDa as determined by SDS-PAGE. CGH II exhibited a high substrate specificity towards cardenolide disaccharides, especially to those with a 1-4-β-linked glucose-digitoxose moiety such as glucoevatromonoside. The K_m- and V_max-values for this particular substrate were calculated to be 101 μM and 19.8 nkat·mg^–1 protein, respectively.     

Diet and physiological responses of Spondyliosoma cantharus (Linnaeus, 1758) to the Caulerpa racemosa var. cylindracea invasion

Marine invasions are a worldwide problem that involves changes in communities and the acclimation of organisms to them. The invasive Chlorophyte Caulerpa racemosa var. cylindracea is widespread in the Mediterranean and colonises large areas from 0 to 70 m in depth. The omnivorous fish Spondyliosoma cantharus presents a high frequency of occurrence of C. racemosa in the stomach contents at invaded areas (76.3%) while no presence of C. racemosa was detected in control areas. The isotopic composition of muscle differed significantly between invaded and non-invaded sites for δ¹³C (− 16.67‰ ± 0.09 and − 17.67‰ ± 0.08, respectively), δ¹⁵N (10.22‰ ± 0.22 and 9.32‰ ± 0.18, respectively) and the C:N ratio (2.01 ± 0.0002 and 1.96 ± 0.009, respectively). Despite the high frequency of occurrence of C. racemosa in the stomach contents of S. cantharus and its important contribution to the δ¹³C source (20.7% ± 16.2), the contribution of C. racemosa to the δ¹⁵N in S. cantharus food sources was very low (6.6% ± 5.8). Other invertebrate prey such as decapods and polychaetes were more important contributors to the δ¹⁵N source at both invaded and non-invaded sites. Activation of enzymatic pathways (catalase, superoxide dismutase, glutathione-s-tranferase, 7-ethoxy resorufin O-de-ethylase) but not a significant increase in lipid peroxidation MDA (0.49 ± 0.01 nmol/mg prot at non-invaded and 0.53 ± 0.01 nmol/mg prot at invaded sites) was observed in S. cantharus individuals living in C. racemosa-invaded sites compared with control specimens. The low δ¹⁵N contribution values of C. racemosa by S. cantharus together with the toxicity demonstrated by the activation of the antioxidant defences and the important contribution of invertebrate prey to the δ¹⁵N could mean that the ingestion of C. racemosa by S. cantharus might be unintentional during the predation of invertebrate preys living underneath the entanglement of the C. racemosa fronds and stolons mats.     

Pronase digestion of brush border membrane-bound Cry1Aa shows that almost the whole activated Cry1Aa molecule penetrates into the membrane

Bacillus thuringiensis insecticidal proteins, Cry toxins, following ingestion by insect larvae, induce insecticidal effect by penetrating the brush border membranes (BBM) of midgut epithelial cells. Purified, activated B. thuringiensis Cry1Aa bound to Bombyx mori BBMV or unbound Cry1Aa were vigorously digested with Pronase. Both digests were compared by Western blotting. Free Cry1Aa was digested to α-helix and/or to amino acids at 1 mg Pronase/mL within 2.4 h at 37 °C. Whereas, BBMV-bound Cry1Aa was very resistant to Pronase digestion and even at 2 mg for 24 h, 7.5 kDa and 30 kDa peptide were detected by α-2,3 antiserum, and α-4,5 and α-6,7 antisera, respectively. Another 30 kDa peptide was also detected by β-6-11 and domain III antisera. These fragments are believed either to be embedded in or to strongly interact with the BBMV. The 7.5 and former 30 kDa peptides are thought to be derived from α-2,3 helix and stretch of α-4 to α-7 helices. Furthermore the latter 30 kDa was thought to include the stretch of β-6 to domain III. Moreover, the embedded Cry1Aa molecule appears to be segregated in some areas of β-1-5 sheets, resulting in the above two 30 kDa peptides. From these digestion patterns, we proposed new membrane insertion model for single Cry1Aa molecule. On the other hand, in digestion of BBMV-bound Cry1Aa, 15 kDa peptide which was recognized only by α-4,5 antiserum was observed. This fragment must be dimeric α-4,5 helices and we discussed the origin of this peptide.     

Mutations and modifications support a ‘pitted-flexiball’ model for α-crystallin

α-Crystallin is renown for resisting crystallization and electron microscopic image analysis. The spatial conformation thus remaining elusive, the authors explored the structure and chaperone functioning by analyzing the effects of site-directed mutagenesis, the properties of naturally occurring aberrant forms of α-crystallin and the influence of chemical modifications. The authors observed that the globular multimeric structure, as well as the chaperoning capacity are remarkably tolerant towards changes and modifications in the primary structure. The essential features of the quaternary structure—globular shape, flexibility, highly polar exterior and accessible hydrophobic surface pockets—support a ‘pitted-flexiball’ model, which combines tetrameric subunit building blocks in an open micelle-like arrangement.     

Thin layer chromatographic analysis of glucose and maltose in estivated Biomphalaria glabrata snails and those infected with Schistosoma mansoni

Thin layer chromatography was used to analyze the glucose and maltose concentrations of the digestive gland–gonad complex (DGG) of uninfected-estivated Biomphalaria glabrata snails and estivated B. glabrata patently infected with Schistosoma mansoni. All snails were estivated in a most chamber at a relative humidity of 98 ± 1% and a temperature of 23 ± 1 °C for 14 days. Carbohydrates were extracted from the DGG with 70% aqueous ethanol, and extracts were analyzed on silica gel preadsorbent plates using ethyl acetate–glacial acetic acid–methanol–water (60:15:15:10) mobile phase, α-naphthol–sulfuric acid detection reagent, and quantification by densitometry. The concentrations of glucose and maltose were significantly reduced in both uninfected-estivated snails and infected-estivated snails.     

Effects of acute temperature or salinity stress on the immune response in sea cucumber, Apostichopus japonicus

Invertebrates are increasingly raised in mariculture, where it is important to monitor immune function and to minimize stresses that could suppress immunity. The activities of phagocytosis, superoxide dismutase (SOD), catalase (CAT), myeloperoxidase (MPO), and lysozyme (LSZ) were measured to evaluate the immune capacities of the sea cucumber, Apostichopus japonicus, to acute temperature changes (from 12 °C to 0 °C, 8 °C, 16 °C, 24 °C, and 32 °C for 72 h) and salinity changes (from 30‰ to 20‰, 25‰, and 35‰ for 72 h) in the laboratory. Phagocytosis was significantly affected by temperature increases in 3 h, and by salinity (25‰ and 35‰) changes in 1 h. SOD activities decreased significantly in 0.5 h to 6 h samples at 24 °C. At 32 °C, SOD activities decreased significantly in 0.5 h and 1 h exposures, and obviously increased for 12 h exposure. CAT activities decreased significantly at 24 °C for 0.5 h exposure, and increased significantly at 32 °C in 3 h to 12 h exposures. Activities of MPO increased significantly at 0 °C in 0.5 h to 6 h exposures and at 8 °C for 1 h. By contrast, activities of MPO decreased significantly in 24 °C and 32 °C treatments. In elevated-temperature treatments, activities of LSZ increased significantly except at 32 °C for 6 h to 12 h exposures. SOD activity was significantly affected by salinity change. CAT activity decreased significantly after only 1 h exposure to salinity of 20‰. Activities of MPO and LSZ showed that A. japonicus tolerates limited salinity stress. High-temperature stress had a much greater effect on the immune capacities of A. japonicus than did low-temperature and salinity stresses.     

Characterization of the heat shock protein 90 gene in the plant parasitic nematode Meloidogyne artiellia and its expression as related to different developmental stages and temperature

The full-length cDNA and the corresponding gene of the heat shock protein 90, Mt-Hsp90, were isolated and characterized in the plant parasitic nematode Meloidogyne artiellia. The full-length Mt-Hsp90 cDNA contained a 5′ untranslated region (UTR) of 45 bp with the 22 bp trans-spliced leader SL1, an ORF of 2172 bp encoding a polypeptide of 723 amino acids and a 3′ UTR of 191 bp. The deduced amino acid sequence of Mt-hsp90 showed high similarity with other known Hsp90s. Five conserved amino acid signatures indicated that Mt-hsp90 is a cytosolic member of the Hsp90 family. The gene consists of 10 exons and 9 introns, a more expanded gene structure compared to the corresponding Caenorhabditis elegans gene, daf-21. Mt-hsp90 gene was constitutively expressed at high levels in all developmental stages of M. artiellia. Egg masses and second stage juveniles (J2s) were exposed at 5° and 30 °C for different periods of times in order to explore the impact of adverse temperature on Mt-hsp90 gene expression. Expression levels of Mt-hsp90 were examined by fluorescent real-time PCR. At 30 °C a burst of expression for Mt-hsp90 was observed in J2s after 2 h of heat shock treatment, then expression dropped with longer exposing times, although remaining still relatively high after 24 h. This temperature did not affect Mt-hsp90 gene expression in the egg masses. However, egg masses exposed at 5 °C showed a little but gradual increase in the mRNA level with time. By contrast, no significant changes in the Mt-hsp90 level were observed in J2s exposed to cold. These data show that egg masses and J2s exposed to cold and heat stresses have different expression profiles suggesting that Mt-Hsp90 may provide a link between environmental conditions and the life cycle of the nematode.     

Interaction of DNA with bovine lens α-crystallin: its functional implications

Under normal conditions, lens aggregates of α-crystallin subunits, αA and αB, are found in the cytoplasm. However, during stress in nonlenticular tissues, αB translocates to the nucleus. A sequence study revealed that both subunits share a consensus sequence with other DNA binding proteins. These observations prompted us to investigate DNA binding with α-crystallin by UV-mediated photo-crosslinking. The data show that both single and double stranded DNA crosslink mainly with tetramers of α-crystallin subunits. The formation of tetramers appears to modify α-crystallin interactive properties and, therefore, its induction may have functional significance. These observations suggest that α-crystallin may have a nuclear function which includes DNA binding.     

Enzymatic characterization of the Plasmodium vivax chitinase, a potential malaria transmission-blocking target

The chitinase (EC 3.2.1.14) of the human malaria parasite Plasmodium falciparum, PfCHT1, has been validated as a malaria transmission-blocking vaccine (TBV). The present study aimed to delineate functional characteristics of the P. vivax chitinase PvCHT1, whose primary structure differs from that of PfCHT1 by having proenzyme and chitin-binding domains. The recombinant protein rPvCHT1 expressed with a wheat germ cell-free system hydrolyzed 4-methylumbelliferone (4MU) derivatives of chitin oligosaccharides (β-1,4-poly-N-acetyl glucosamine (GlcNAc)). An anti-rPvCHT1 polyclonal antiserum reacted with in vitro-obtained P. vivax ookinetes in anterior cytoplasm, showing uneven patchy distribution. Enzymatic activity of rPvCHT1 shared the exclusive endochitinase property with parallelly expressed rPfCHT1 as demonstrated by a marked substrate preference for 4MU-GlcNAc₃ compared to shorter GlcNAc substrates. While rPvCHT1 was found to be sensitive to the general family-18 chitinase inhibitor, allosamidin, its pH (maximal in neutral environment) and temperature (max. at ~ 25 °C) activity profiles and sensitivity to allosamidin (IC₅₀ = 6 µM) were different from rPfCHT1. The results in this first report of functional rPvCHT1 synthesis indicate that the P. vivax chitinase is enzymatically close to long form Plasmodium chitinases represented by P. gallinaceum PgCHT1.     

Growth and protein synthesis of barramundi, Lates calcarifer, fed lupin as a partial protein replacement

Protein synthesis is an essential growth process in all animals. Little information is available on post-prandial protein synthesis and even less where different protein sources are compared. Protein synthesis was measured at 4 and 24 h after feeding juvenile barramundi in order to determine the effect of using lupin as a partial protein replacement for fish meal on the post-prandial protein metabolism. Juvenile barramundi (4.3 ±0.6 g) were held in a recirculation system (27 °C, salinity 10‰ and 24 h light) for 15 days. Fish were fed one of two isonitrogenous isoenergetic diets (40% crude protein, 16% lipid and 18.5 GE MJ kg^− 1). One diet was formulated with 100% fish meal as the protein source while the other had 45% of the protein replaced with lupin ingredients (lupin kernel meal (Lupinus angustifolius) and lupin protein concentrate). All fish were fed a ration of 6%·d^− 1 and feed intake was not significantly different between the two diets. Specific growth rate (SGR) and growth efficiency (in relation to protein (PPV) and energy (PEV)) were 6.5 ± 0.14%·d^− 1, 43.8 ± 2.72% and 38.31 ± 1.56%, respectively, and were not significantly different between the two diets. There was no significant difference in protein synthesis between the two diets at 4 and 24 h after feeding, however protein synthesis was significantly higher 4 h after feeding than at 24 h (p = 0.02). Neither growth performance nor protein metabolism was altered by replacing 45% of the protein with lupin protein and indicated this to be a suitable protein source for barramundi feeds.     

Endogenous C-terminal fragments of beta-amyloid precursor protein from Xenopus laevis skin exudate

Using a monoclonal antibody against the entire C-terminal end of human APP₆₉₅ (643–695 sequence) and a monoclonal antibody directed against human β[1–40] amyloid peptide (βA), we show the existence of endogenous peptides proteolytically derived from APP in skin exudate of the non transgenic Xenopus laevis frog. The majority of the immunoreactivity is found associated with a 30 kDa molecular species. Biochemical fractionation followed by mass spectrometry identification allowed us to assign this molecular species to C-terminal APP fragments containing all or part of βA. According to the nature of N- and C-terminal amino acids we identified endogenous β-, γ-, ε-secretase-like activities, caspase-like activity and numerous endogenous cleavage sites within the β-amyloid sequence at same sites as those observed in human βA sequence. All these homologies with human indicate that X. laevis skin exudate is a good natural model to study βA metabolism. In this way, interestingly, we identified endogenous cleavages at prohormone convertase-like sites not yet described at the same sites in human. Finally, all identified peptide fragments were stably associated with a 20.2 kDa protein. These new observed features suggest new research pathways concerning human βA metabolism and carriage of hydrophobic peptide fragments issued from APP processing.     

Characterization of Plasmodium falciparum calcium-dependent protein kinase 4

In Plasmodium berghei, the orthologous gene of P. falciparum calcium-dependent protein kinase 4 (PfCDPK4) was reported to be essential for the exflagellation of male gametocytes. To elucidate the role of PfCDPK4 in P. falciparum gametogenesis, we characterized the biological function of PfCDPK4 in vitro. PfCDPK4 was purified as a fusion protein that was labeled with [γ-³²P]ATP; this labeling was then eliminated by phosphatase. Phosphorylation activity of PfCDPK4 was eliminated when its putative catalytic lysine residue was replaced with alanine. In biochemical analyses, PfCDPK4 was found to have characteristics that were similar to those of homologous proteins from plants. PfCDPK4 phosphorylation was activated when experimental conditions were changed from those characteristic of human blood (37 °C, pH 7.4) to those of the mosquito bloodmeal (at least 5 °C below 37 °C, pH 7.6, with xanthurenic acid (XA)). PfCDPK4 was overexpressed in day 15 gametocytes exposed to XA or human serum. Thus, PfCDPK4 phosphorylation is activated by an increase in Ca²⁺ concentration or pH and by a decrease in temperature, and is associated with the Ca²⁺ signals that facilitate P. falciparum gametogenesis.     

Thermally induced structural changes of intrinsically disordered small heat shock protein Hsp22

We applied different methods (differential scanning calorimetry, circular dichroism, Fourier transform infrared spectroscopy, and intrinsic fluorescence) to investigate the thermal-induced changes in the structure of small heat shock protein Hsp22. It has been shown that this protein undergoes thermal-induced unfolding that occurs within a very broad temperature range (from 27 °C to 80 °C and above), and this is accompanied by complete disappearance of α-helices, significant decrease in β-sheets content, and by pronounced changes in the intrinsic fluorescence. The results confirm predictions that Hsp22 belongs to the family of intrinsically disordered proteins (IDP) with certain parts of its molecule (presumably, in the α-crystallin domain) retaining folded structure and undergoing reversible thermal unfolding. The results are also discussed in terms of downhill folding scenario.     

Thermodynamic stability of bovine α-crystallin in its interactions with other bovine crystallins

Light scattering measurements were performed on dilute solutions of α-crystallin mixed with different combinations of β_H, β_L and γ-fractions of bovine lens crystallins. Light scattering intensities were obtained as a function of scattering angle, concentration and temperature. The temperature dependence of the second virial coefficients was used to obtain partial molar enthalpy and end entropy of solutions. The difference between the thermodynamic parameters of the crystallin mixtures and those of the weighted averages of the individual components yielded the excess enthalpy and entropy functions of the solutions. Both the excess enthalpy and entropy functions indicated that thermodynamic stability of α-crystallin is progressively enhanced by its interactions with γ(β_H+γ)(β_H+β_L+γ) crystallins. The last two combinations showed negative values both for excess enthalpy as well for excess entropy of solutions. Other combinations demonstrated increasing positive values. This implies that the combination of all four crystallins in the vertebrate lens enables the best solvation property as well as the best packing as opposed to any other single or combinatorial arrangements of crystallins. Similar conclusions have been obtained in the past from water and other vapor sorption studies.     

Environmental factors influencing the chaperone-like activity of α-crystallin

The effects of mild environmental changes (e.g. the addition of divalent cations or EDTA, as well as variations of buffer pH) on the heat stability and chaperone-like activity of native α-crystallin, and denatured–renatured α-crystallin in the native molar isoform ratio, have been investigated using circular dichroism (CD) spectropolarimetry and functional assays. The presence or absence of divalent cations has little or no effect on the secondary structure of renatured samples, although chaperone-like activity levels can vary widely; the only relevant spectral difference observed is a loss of some α-helical content in all the renatured samples relative to the native protein, but this change has no impact on function. The range of concentration over which the inhibitory Mg²⁺ effect is observed is 10-fold higher for dialyzed fresh protein than for protein renatured into buffers containing Mg²⁺, but for both sets of samples, the full effect is established below physiological Mg²⁺ concentrations. Renaturing into various pH buffers, in contrast, affects both heat stability and chaperone-like activity below pH 7.0, with essentially no functionality observed at pH 6.0. CD spectra of these samples indicate that acidic conditions lead to some degree of unfolding, and that this unfolding correlates directly with functionality. Similar results are obtained for fresh protein dialyzed against these pH levels. Overall, these results suggest that heat stability is a function of the protein's secondary structure and folding state, while chaperone-like activity is primarily a function of factors at the tertiary and quaternary levels of organization.     

Trehalose accumulation in Baudoinia compniacensis following abiotic stress

Baudoinia compniacensis is a microfungus recently described as the principal agent of fouling known as “warehouse staining”, affecting building exteriors, fixtures and vegetation surfaces in areas proximate to distillery aging warehouses, commercial bakeries and other areas subject to low-level ethanol vapour exposure. The surfaces most affected tend to be highly exposed and undergo extreme diurnal temperature fluctuations. In previous work, we have demonstrated the existence of heat-inducible putative chaperone proteins that may also be induced by low-level exposures to ethanol vapour (e.g., <10 ppm). The present study investigated the cellular accumulation of trehalose, a disaccharide identified in some microorganisms to be important in the protection of cell components during adverse stress conditions, such as thermal stress. Following heat shock at 45 °C, we observed a 2.5-fold accumulation of trehalose relative to unheated controls maintained at 26 °C. Peak trehalose concentrations of 10 mg g⁻¹ dry wt were seen at 90 min after heat treatment, followed by a gradual return to post-treatment by 150 min. Exposure of B. compniacensis cells to ethanol resulted in a similar increased accumulation of trehalose compared to unexposed controls. These findings imply that trehalose may be important in the tolerance of this fungus to abiotic stresses, such as heat and solvent exposure, and suggest future research directions for the control and prevention of warehouse staining.     

Antagonism of Aeromonas hydrophila by propolis and its effect on the performance of Nile tilapia, Oreochromis niloticus

Propolis, a resinous substance collected by Apis mellifera bees from various plant sources and mixed with secreted beeswax, is a multifunctional material used by bees in the construction, maintenance, and protection of their hives. The collected propolis sample, from High Egypt, was dark-green with olive-odor. The minimal inhibition concentration (MIC) of propolis-ethanolic-extract, against Aeromonas hydrophila, was 80 μg Propolis-ethanolic-extract and crude propolis (1%) were added to artificial basal diet with (30% crude protein) to evaluate their efficacy on the fish growth-performance, immunostimulation and resistance to A. hydrophila. Two hundred and twenty-five Oreochromis niloticus (8 ± 0.45 g/fish) were divided into three equal treatments (T) of triplet replicates. The fish of T₁ were fed on basal diet (control). The fish of T₂ were given the basal diet, containing propolis-ethanolic-extract. The fish of T₃ were given the basal diet containing crude propolis for 28 day. The fish were intraperitoneally challenged by A. hydrophila (0.2 × 10⁷ cells ml⁻¹) at the end of the feeding period and kept for 15 more days.The best growth rate and feed conversion ratio were obtained with T_2. The increase in the average daily gain, specific growth rate and feed efficiency ratio were highly significances in T₂ followed by T₃ when compared with the control group. The HCT-level and monocyte-counts were increased (T₂). No significant change, in the large lymphocytic-count was found among the three treatments (28–27–28%), while the neutrophil-count was significantly decreased (7%) with T₂ and increased (13.11%) with the control. A significant increase in serum lysozyme and serum bactericidal activities was found with T₂. The RLP against A. hydrophila was high with T₂ and T₃.The propolis-ethanolic-extract enhanced the growth, immunity and resistance of O. niloticus against A. hydrophila more than the crude propolis.     

Genealogy of the α-crystallin—small heat-shock protein superfamily

Sequences of 40 very diverse representatives of the α-crystallin–small heat-shock protein (α-Hsp) superfamily are compared. Their characteristic C-terminal ‘α-crystallin domain' of 80–100 residues contains short consensus sequences that are highly conserved from prokaryotes to eukaryotes. There are, in addition, some positions that clearly distinguish animal from non-animal α-Hsps. The α-crystallin domain is predicted to consist of two hydrophobic β-sheet motifs, separated by a hydrophilic region which is variable in length. Combination of a conserved α-crystallin domain with a variable N-terminal domain and C-terminal extension probably modulates the properties of the various α-Hsps as stress-protective and structural oligomeric proteins. Phylogeny reconstruction indicates that multiple α-Hsps were already present in the last common ancestor of pro- and eukaryotes. It is suggested that during eukaryote evolution, animal and non-animal α-Hsps originated from different ancestral gene copies. Repeated gene duplications gave rise to the multiple α-Hsps present in most organisms.