Dehydration and cold hardiness in the Arctic Collembolan Onychiurus arcticus Tullberg 1876

Specimens of the Arctic Collembolon Onychiurus arcticus were exposed to desiccation at several subzero temperatures over ice and at 0.5 °C over NaCl solutions. The effects of desiccation on water content (WC), body fluid melting point (MP), supercooling point (SCP) and survival were studied at several acclimation temperatures and relative humidities. Exposure to temperatures down to −19.5 °C caused a substantial and increasing dehydration. At the lowest exposure temperature unfrozen individuals lost 91.6% of the WC at full hydration but more than 80% of the individuals survived when rehydrated. Exposure at 0.5 °C to decreasing relative humidities (RH) from 100% to 91.3% caused increasing dehydration and increasing mortality. Survival of equally dehydrated individuals was higher at subzero temperatures than at 0.5 °C. Concurrent with the decline in WC a lowering of the MP was observed. Animals exposed to −3 °C and −6 °C over ice for 31 days had a MP of −3.8 and < −7.5 °C, respectively. Specimens from a laboratory culture had a mean SCP of −6.1 °C, and acclimation at 0 or −3 °C had little effect on SCPs. Exposure at −8.2 °C over ice for 8 days, however, caused the mean SCP to decline to −21.8 °C due to the severe dehydration of these individuals. Dehydration at 0.5 °C in 95.1 and 93.3% RH also caused a decline in SCPs to about −18 °C. Individuals that had been acclimated over ice at −12.4 °C or at lower temperatures apparently did not freeze at all when cooled to −30 °C, probably because all freezeable water had been lost. These results show that O. arcticus will inevitably undergo dehydration when exposed to subzero temperatures in its natural frozen habitat. Consequently, the MP and SCP of the Collembola are substantially lowered and in this way freezing is avoided. The increased cold hardiness by dehydration is similar to the protective dehydration mechanism described in earthworm cocoons and Arctic enchytraeids. Accepted: 5 January 1998     

Extracellular Poly(α-L-guluronate)lyase from Corynebacterium sp.: Purification, Characteristics, and Conformational Properties

Extracellular alginate lyase was purified from the culture supernatant of Corynebacterium sp. isolated from the sewage of a sea tangle processing factory in order to elucidate the structure—function relationship of alginate lyase. The electrophoretically homogeneous enzyme was shown to have a molecular mass of 27 kDa by sodium dodecyl sulfate (SDS)—polyacrylamide gel electrophoresis (PAGE) and by gel filtration, with an isoelectric point of 7.3. The molecular mass from amino acid analysis was 28.644 kDa. The optimal pH and temperature for the enzyme reaction were around 7.0 and 55°C, respectively. Metal compounds such as MnCl₂ and NiCl₂ increased the enzyme activity. The enzyme was identified as the endolytic poly(-L-guluronate)lyase, which was active on poly(-L-1,4-guluronate) and caused a rapid decrease in the viscosity of alginate solution. Measurement of the far-UV circular dichroic spectrum of the enzyme molecule gave a spectrum with a deep trough at 215nm accompanied by a shallow one at around 237 nm, and with a high peak at 197 nm and a much lower one at 230 nm. This spectrum was most likely to be that of the -form of the enzyme molecule and resembled poly(-D-mannuronate)lyase from Turbo cornutus (wreath shell) and poly(-L-guluronate)lyase from Vibrio sp. (marine bacterium). The near-UV circular dichroic spectrum was characteristic for aromatic amino acid residues. In the presence of 6 M urea, these spectra changed drastically in the near-UV and a little in the far-UV with the disappearance of the enzyme activity. Removal of the denaturant in the enzyme solution by dialysis restored both the activity and inherent circular dichroic spectra. The -sheets observed in alginate lyases as the major ordered structure seem to be a common conformation for the lyases.     

Supercooling point plasticity during cold storage in the freeze‐tolerant sugarbeet root maggot Tetanops myopaeformis

Abstract The sugarbeet root maggot Tetanops myopaeformis (Röder) overwinters as a freeze‐tolerant third‐instar larva. Although most larvae are considered to overwinter for only 1 year, some may exhibit prolonged diapause in the field. In the laboratory, they can live for over 5 years using a combination of diapause and post‐diapause quiescence. In the present study, the cold survival strategies of these larvae during storage is investigated by measuring their supercooling points in combination with survival data. Supercooling points (SCPs) change significantly during storage, highlighted by a marked increase in the range of SCPs recorded, although the ability to tolerate freezing is not affected. Additionally, a freezing event ‘re‐focuses’ the SCPs of aged larvae to levels similar to those seen at diapause initiation. This change in SCPs is dependant not only on the initial freezing event, but also on the parameters of the incubation period between freezing events. Finally, the temperatures of larval overwintering microhabitats are monitored during the 2007–2008 boreal winter. The results indicate that, although overwintering larva are physiologically freeze‐tolerant, they may essentially be freeze avoidant during overwintering via microhabitat selection.     

Absolute quantification of DcR3 and GDF15 from human serum by LC‐ESI MS

Biomarkers are widely used in clinical diagnosis, prognosis and therapy monitoring. Here, we developed a protocol for the efficient and selective enrichment of small and low concentrated biomarkers from human serum, involving a 95% effective depletion of high‐abundant serum proteins by partial denaturation and enrichment of low‐abundant biomarkers by size exclusion chromatography. The recovery of low‐abundance biomarkers was above 97%. Using this protocol, we quantified the tumour markers DcR3 and growth/differentiation factor (GDF)15 from 100 μl human serum by isotope dilution mass spectrometry, using ¹⁵N metabolically labelled and concatamerized fingerprint peptides for the both proteins. Analysis of three different fingerprint peptides for each protein by liquid chromatography electrospray ionization mass spectrometry resulted in comparable concentrations in three healthy human serum samples (DcR3: 27.23 ± 2.49 fmol/ml; GDF15: 98.11 ± 0.49 fmol/ml). In contrast, serum levels were significantly elevated in tumour patients for DcR3 (116.94 ± 57.37 fmol/ml) and GDF15 (164.44 ± 79.31 fmol/ml). Obtained data were in good agreement with ELISA and qPCR measurements, as well as with literature data. In summary, our protocol allows the reliable quantification of biomarkers, shows a higher resolution at low biomarker concentrations than antibody‐based strategies, and offers the possibility of multiplexing. Our proof‐of‐principle studies in patient sera encourage the future analysis of the prognostic value of DcR3 and GDF15 for colon cancer patients in larger patient cohorts.     

Thermal denaturation and aggregation of apoform of glycogen phosphorylase b. Effect of crowding agents and chaperones

The effect of protein and chemical chaperones and crowders on thermal stability and aggregation of apoform of rabbit muscle glycogen phosphorylase b (apoPhb) has been studied at 37°C. Proline suppressed heat‐induced loss in ability of apoPhb to reconstitution at 37°C, whereas α‐crystallin did not reveal a protective action. To compare the antiaggregation activity of intact and crosslinked α‐crystallins, an adsorption capacity (AC) of a protein chaperone with respect to a target protein was estimated. This parameter is a measure of the antiaggregation activity. Crosslinking of α‐crystallin results in 11‐fold decrease in the initial AC. The nonlinear character of the relative initial rate of apoPhb aggregation versus the [intact α‐crystallin]/[apoPhb] ratio plot is indicative of the decrease in the AC of α‐crystallin with increasing the [α‐crystallin]/[apoPhb] ratio and can be interpreted as an evidence for dynamic chaperone structure and polydispersity of α‐crystallin–target protein complexes. As for chemical chaperones, a semisaturation concentration of the latter was used as a characteristic of the antiaggregation activity. A decrease in the semisaturation concentration for proline was observed in the presence of the crowders (polyethylene glycol and Ficoll‐70). © 2013 Wiley Periodicals, Inc. Biopolymers 101: 504–516, 2014.     

Stabilization of collagen through bioconversion: An insight in protein–protein interaction

Collagen is a natural protein, which is used as a vital biomaterial in tissue engineering. The major concern about native collagen is lack of its thermal stability and weak resistance to proteolytic degradation. In this scenario, the crosslinking compounds used for stabilization of collagen are mostly of chemical nature and exhibit toxicity. The enzyme mediated crosslinking of collagen provides a novel alternative, nontoxic method for stabilization. In this study, aldehyde forming enzyme (AFE) is used in the bioconversion of hydroxylmethyl groups of collagen to formyl groups that results in the formation of peptidyl aldehyde. The resulted peptidyl aldehyde interacts with bipolar ions of basic amino acid residues of collagen. Further interaction leads to the formation of conjugated double bonds (aldol condensation involving the aldehyde group of peptidyl aldehyde) within the collagen. The enzyme modified collagen matrices have shown an increase in the denaturation temperature, when compared with native collagen. Enzyme modified collagen membranes exhibit resistance toward collagenolytic activity. Moreover, they exhibited a nontoxic nature. The catalytic activity of AFE on collagen as a substrate establishes an efficient modification, which enhances the structural stability of collagen. This finds new avenues in the context of protein–protein stabilization and discovers paramount application in tissue engineering. © 2014 Wiley Periodicals, Inc. Biopolymers 101: 903–911, 2014.     

More stable structure of wheat germ lipase at low pH than its native state

Wheat germ lipase is a cereal lipase which is a monomeric protein. In the present study we sought to structurally characterize this protein along with equilibrium unfolding in solution. Conformational changes occurring in the protein with varying pH, were monitored by circular dichroism (CD) spectroscopy, fluorescence emission spectroscopy, binding of hydrophobic dye, 1-anilino 8-naphthalenesulfonic acid (ANS) and dynamic light scattering (DLS). Our study showed that acid denaturation of lipase lead to characterization of multiple monomeric intermediates. Native protein at pH 7.0 showed far-UV spectrum indicating mixed structure with both alpha and beta-type of characteristics. Activity of lipase was found to fall on either sides of pH 7.0–8.0. Acid-unfolded state was characterized at pH 4.0 with residual secondary structure, disrupted tertiary spectrum and red-shifted fluorescence spectrum with decreased intensity. Further decrease in pH lead to formation of secondary structure and acid-induced molten globule state was found to be stabilized at pH 1.4, with exposed tryptophan residues and hydrophobic patches. Notably, interesting finding of this study was characterization of acid-induced state at pH 0.8 with higher secondary structure content than native lipase, regain in tertiary spectrum and induction of compact conformation. Although enzymatically inactive, acid-induced state at pH 0.8 was found to be structurally more stable than native lipase, as shown by chemical and thermal denaturation profiles.     

Nucleic acid and protein factors involved in Escherichia coli polynucleotide phosphorylase function on RNA

It has been reported that polynucleotide phosphorylase (PNPase) binds to RNA via KH and S1 domains, and at least two main complexes (I and II) have been observed in RNA-binding assays. Here we describe PNPase binding to RNA, the factors involved in this activity and the nature of the interactions observed in vitro. Our results show that RNA length and composition affect PNPase binding, and that PNPase interacts primarily with the 3′ end of RNA, forming the complex I-RNA, which contains trimeric units of PNPase. When the 5′ end of RNA is blocked by a hybridizing oligonucleotide, the formation of complex II-RNA is inhibited. In addition, PNPase was found to form high molecular weight (>440 kDa) aggregates in vitro in the absence of RNA, which may correspond to the hexameric form of the enzyme. We confirmed that PNPase in vitro RNA binding, degradation and polyadenylation activities depend on the integrity of KH and S1 domains. These results can explain the defective in vivo autoregulation of PNPase71, a KH point substitution mutant. As previously reported, optimal growth of a cold-sensitive strain at 18 °C requires a fully active PNPase, however, we show that overexpression of a novel PNPaseΔS1 partially compensated the growth impairment of this strain, while PNPase71 showed a minor compensation effect. Finally, we propose a mechanism of PNPase interactions and discuss their implications in PNPase function.