A cryoprotective and cold-adapted 1,3-β-endoglucanase from cherimoya (Annona cherimola) fruit

Insect fungal pathogens secrete a cell wall-associated glucanase that acts to help avoid recognition by the host immune system

Fungal insect pathogens have evolved diverse mechanisms to evade host immune recognition and defense responses. However, identification of fungal factors involved in host immune evasion during cuticular penetration and subsequent hemocoel colonization remains limited. Here, we report that the entomopathogenic fungus Beauveria bassiana expresses an endo-β-1,3-glucanase (BbEng1) that functions in helping cells evade insect immune recognition/ responses. BbEng1 was specifically expressed during infection, in response to host cuticle and hemolymph, and in the presence of osmotic or oxidative stress. BbEng1 was localized to the fungal cell surface/ cell wall, where it acts to remodel the cell wall pathogen associated molecular patterns (PAMPs) that can trigger host defenses, thus facilitating fungal cell evasion of host immune defenses. BbEng1 was secreted where it could bind to fungal cells. Cell wall β-1,3-glucan levels were unchanged in ΔBbEng1 cells derived from in vitro growth media, but was elevated in hyphal bodies, whereas glucan levels were reduced in most cell types derived from the BbEng1 overexpressing strain (BbEng1OE). The BbEng1OE strain proliferated more rapidly in the host hemocoel and displayed higher virulence as compared to the wild type parent. Overexpression of their respective Eng1 homologs or of BbEng1 in the insect fungal pathogens, Metarhizium robertsii and M. acridum also resulted in increased virulence. Our data support a mechanism by which BbEng1 helps the fungal pathogen to evade host immune surveillance by decreasing cell wall glucan PAMPs, promoting successful fungal mycosis.

Antihyperglycemic Activity of the Leaves from Annona cherimola Miller and Rutin on Alloxan-induced Diabetic Rats

Background:

Annona cherimola, known as “chirimoya” has been reported in Mexican traditional medicine for the treatment of diabetes.

Objective:

The aims of the present study were to validate and assess the traditional use of A. cherimola as an antidiabetic agent.

Materials and Methods:

The ethanol extract from A. cherimola (300 mg/kg, EEAc), subsequent fractions (100 mg/kg), and rutin (30 mg/kg) were studied on alloxan-induced type 2 diabetic (AITD) and normoglycemic rats. In addition, oral glucose tolerance test (OGTT) and oral sucrose tolerance test (OSTT) were performed in normoglycemic rats. Molecular docking technique was used to conduct the computational study.

Results:

Bioassay-guided fractionation of EEAc afforded as major antihyperglycemic compound, rutin. EEAc attenuated postprandial hyperglycemia in acute test using AITD rats (331.5 mg/dL) carrying the glycemic levels to 149.2 mg/dL. Rutin after 2 h, attenuated postprandial hyperglycemia in an acute assay using AITD rats such as EEAc, with maximum effect (150.0 mg/dL) being seen at 4 h. The antihyperglycemic activities of EEAc and rutin were comparable with acarbose (151.3 mg/dL). In the subchronic assay on AITD rats, the EEAc and rutin showed a reduction of the blood glucose levels since the 1^st week of treatment, reaching levels similar to normoglycemic state (116.9 mg/kg) that stayed constant for the rest of the assay. OGTT and OSTT showed that EEAc and rutin significantly lowered blood glucose levels in normoglycemic rats at 2 h after a glucose or sucrose load such as acarbose. Computational molecular docking showed that rutin interacted with four amino acids residues in the enzyme α-glucosidase.

Conclusion:

The results suggest that rutin an α-glucosidase inhibitor was responsible in part of the antihyperglycemic activity of A. cherimola. Its in vivo antihyperglycemic activity is in good agreement with the traditional use of A. cherimola for the treatment of diabetes.

SUMMARY

The ethanol extract from Annona cherimola (300 mg/kg, EEAc), subsequent fractions (100 mg/kg) and rutin (30 mg/kg) were studied on alloxan-induced type 2 diabetic (AITD) and normoglycemic rats. The results suggest that rutin; an α-glucosidase inhibitor was responsible in part of the antihyperglycemic activity of A. cherimola. Its in vivo antihyperglycemic activity is in good agreement with the traditional use of A. cherimola for the treatment of diabetes.

Abbreviations Used: EEAc: The ethanol extract from Annona cherimola, AITD: Alloxan-induced type 2 diabetic rats, OGTT: Oral glucose tolerance test, OSTT: Oral sucrose tolerance test, DM: Diabetes mellitus

Purification, characterization and synergism in autolysis of a group of 1,3-β-glucan hydrolases from the pilei of Coprinopsis cinerea fruiting bodies

Using a combined chromatography method, we simultaneously purified three protein fractions (II-2, II-3 and II-4) with 1,3-β-glucanase activity from extraction of pilei of Coprinopsis cinerea fruiting bodies. MALDI-TOF/TOF amino acid sequencing showed that these three fractions matched a putative exo-1,3-β-glucanase, a putative glucan 1,3-β-glucosidase and a putative glycosyl hydrolase family 16 protein annotated in the C. cinerea genome, respectively; however, they were characterized as a 1,3-β-glucosidase, an exo-1,3-β-glucanase and an endo-1,3-β-glucanase, respectively, by analysis of their substrate specificities and modes of action. This study explored how these three 1,3-β-glucoside hydrolases synergistically acted on laminarin: the endo-1,3-β-glucanase hydrolysed internal glycosidic bonds of laminarin to generate 1,3-β-oligosaccharides of various lengths, the exo-1,3-β-glucanase cleaved the longer-chain laminarioligosaccharides into short-chain disaccharides, laminaribiose and gentiobiose, and the 1,3-β-glucosidase further hydrolysed laminaribiose to glucose. The remaining gentiobiose must be hydrolysed by other 1,6-β-glucosidases. Therefore, the endo-1,3-β-glucanase, exo-1,3-β-glucanase and 1,3-β-glucosidase may act synergistically to completely degrade the 1,3-β-glucan backbone of the C. cinerea cell wall during fruiting body autolysis. These three 1,3-β-glucoside hydrolases share a similar optimum pH and optimum temperature, supporting the speculation that these enzymes work together under the same conditions to degrade 1,3-β-glucan in the C. cinerea cell wall during fruiting body autolysis.

Differential regulation of dehydrin expression and trehalose levels in Cardinal table grape skin by low temperature and high CO2

Dehydrins and trehalose are multifunctional protective biomolecules that play a role in counteracting cellular damage during dehydrative stresses. In this paper, we studied dehydrin isoform patterns, dehydrin gene expression and trehalose levels in the skin of Cardinal (Vitis vinifera L.) table grapes, along with their regulation by different cold postharvest storage conditions. Immunoanalysis with K-segment antibody recognizes four constitutive dehydrins (from 17 to 44 kDa) that are tightly regulated by low temperature and high CO2. Phosphatase treatment showed that DHN44 and DHN22 isoforms are phosphorylated polypeptides, while MALDI-TOF MS and MS/MS analysis suggested that 44 kDa polypeptide may be a dehydrin homodimer. At the transcriptional level, dehydrins are also regulated by low temperature and high CO2, showing a fairly good correlation with their mRNA levels. Trehalose was quantified by high performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), revealing a progressive increase of this metabolite throughout storage at 0 °C and the sudden transitory increases in short-term high CO2-treated fruit. We propose that the constitutive presence and up-regulation of dehydrins and trehalose during low temperature postharvest storage could be positively correlated with the relative chilling tolerance of table grapes and the adaptive responses activated by high CO2 levels to preserve cell water status and to counteract the disruption of physiological processes during cold storage.

Two cold-induced family 19 glycosyl hydrolases from cherimoya (Annona cherimola) fruit: an antifungal chitinase and a cold-adapted chitinase

Two cold-induced chitinases were isolated and purified from the mesocarp cherimoyas (Annona cherimola Mill.) and they were characterised as acidic endochitinases with a Mr of 24.79 and 47.77kDa (AChi24 and AChi48, respectively), both family 19 glycosyl hydrolases. These purified chitinases differed significantly in their biochemical and biophysical properties. While both enzymes had similar optimal acidic pH values, AChi24 was enzymatically active and stable at alkaline pH values, as well as displaying an optimal temperature of 45°C and moderate thermostability. Kinetic studies revealed a great catalytic efficiency of AChi24 for oligomeric and polymeric substrates. Conversely, AChi48 hydrolysis showed positive co-operativity that was associated to a mixture of different functional oligomeric states through weak transient protein interactions. The rise in the AChi48 kcat at increasing enzyme concentrations provided evidence of its oligomerisation. AChi48 chitinase was active and stable in a broad acidic pH range, and while it was relatively labile as temperatures increased, with an optimal temperature of 35°C, it retained about 50% of its maximal activity from 5 to 50°C. Thermodynamic characterisation reflected the high kcat of AChi48 and the remarkably lower ΔH(‡), ΔS(‡) and ΔG(‡) values at 5°C compared to AChi24, indicating that the hydrolytic activity of AChi48 was less thermodependent. In vitro functional studies revealed that AChi24 had a strong antifungal defence potential against Botrytis cinerea, whereas they displayed no cryoprotective or antifreeze activity. Hence, based on biochemical, thermodynamic and functional data, this study demonstrates that two acidic endochitinases are induced at low temperatures in a subtropical fruit, and that one of them acts in an oligomeric cold-adapted manner.