Purification and partial biochemical characterization of a membrane-bound type II-like α-glucosidase from the yeast morphotype of Sporothrix schenckii

Fungal Glycosidases in Sporothrix Species and Candida albicans

Glycoside hydrolases (GHs) are enzymes that participate in many biological processes of fungi and other organisms by hydrolyzing glycosidic linkages in glycosides. They play fundamental roles in the degradation of carbohydrates and the assembly of glycoproteins and are important subjects of studies in molecular biology and biochemistry. Based on amino acid sequence similarities and 3-dimensional structures in the carbohydrate-active enzyme (CAZy), they have been classified in 171 families. Members of some of these families also exhibit the activity of trans-glycosydase or glycosyl transferase (GT), i.e., they create a new glycosidic bond in a substrate instead of breaking it. Fungal glycosidases are important for virulence by aiding tissue adhesion and colonization, nutrition, immune evasion, biofilm formation, toxin release, and antibiotic resistance. Here, we review fungal glycosidases with a particular emphasis on Sporothrix species and C. albicans, two well-recognized human pathogens. Covered issues include a brief account of Sporothrix, sporotrichosis, the different types of glycosidases, their substrates, and mechanism of action, recent advances in their identification and characterization, their potential biotechnological applications, and the limitations and challenges of their study given the rather poor available information.

Insight into broad substrate specificity and synergistic contribution of a fungal α-glucosidase in Chinese Nong-flavor daqu

BACKGROUND

Chinese Nong-favor daqu, the presentative liquor starter of Baijiu, has been enriched with huge amounts of enzymes in degrading various biological macromolecules by openly man-made process for thousand years. According to previous metatranscriptomics analysis, plenty of α-glucosidases were identified to be active in NF daqu and played the key role in degrading starch under solid-state fermentation. However, none of α-glucosidases was characterized from NF daqu, and their actual functions in NF daqu were still unknown.

RESULTS

An α-glucosidase (NFAg31A, GH31-1 subfamily), the second highest expressed α-glucosidases in starch degradation of NF daqu, was directly obtained by heterologous expression in Escherichia coli BL21 (DE3). NFAg31A exhibited the highest sequence identities of 65.8% with α-glucosidase II from Chaetomium thermophilum, indicating its origin of fungal species, and it showed some similar features with homologous α-glucosidase IIs, i.e., optimal activity at pH ~ 7.0 and litter higher temperature of 45 ℃, well stability at 41.3 ℃ and a broad pH range of pH 6.0 to pH 10.0, and preference on hydrolyzing Glc-α1,3-Glc. Besides this preference, NFAg31A showed comparable activities on Glc-α1,2-Glc and Glc-α1,4-Glc, and low activity on Glc-α1,6-Glc, indicating its broad specificities on α-glycosidic substrates. Additionally, its activity was not stimulated by any of those detected metal ions and chemicals, and could be largely inhibited by glucose under solid-state fermentation. Most importantly, it exhibited competent and synergistic effects with two characterized α-amylases of NF daqu on hydrolyzing starch, i.e., all of them could efficiently degrade starch and malto-saccharides, two α-amylases showed advantage in degrading starch and long-chain malto-saccharides, and NFAg31A played the competent role with α-amylases in degrading short-chain malto-saccharides and the irreplaceable contribution in hydrolyzing maltose into glucose, thus alleviating the product inhibitions of α-amylases.

CONCLUSIONS

This study provides not only a suitable α-glucosidase in strengthening the quality of daqu, but also an efficient way to reveal roles of the complicated enzyme system in traditional solid-state fermentation. This study would further stimulate more enzyme mining from NF daqu, and promote their actual applications in solid-state fermentation of NF liquor brewing, as well as in other solid-state fermentation of starchy industry in the future.

Discovery of a Kojibiose Hydrolase by Analysis of Specificity-Determining Correlated Positions in Glycoside Hydrolase Family 65

The Glycoside Hydrolase Family 65 (GH65) is an enzyme family of inverting α-glucoside phosphorylases and hydrolases that currently contains 10 characterized enzyme specificities. However, its sequence diversity has never been studied in detail. Here, an in-silico analysis of correlated mutations was performed, revealing specificity-determining positions that facilitate annotation of the family’s phylogenetic tree. By searching these positions for amino acid motifs that do not match those found in previously characterized enzymes from GH65, several clades that may harbor new functions could be identified. Three enzymes from across these regions were expressed in E. coli and their substrate profile was mapped. One of those enzymes, originating from the bacterium Mucilaginibacter mallensis, was found to hydrolyze kojibiose and α-1,2-oligoglucans with high specificity. We propose kojibiose glucohydrolase as the systematic name and kojibiose hydrolase or kojibiase as the short name for this new enzyme. This work illustrates a convenient strategy for mapping the natural diversity of enzyme families and smartly mining the ever-growing number of available sequences in the quest for novel specificities.

Simple Indolizidine and Quinolizidine Alkaloids

This review of simple indolizidine and quinolizidine alkaloids (i.e., those in which the parent bicyclic systems are in general not embedded in polycyclic arrays) is an update of the previous coverage in Volume 55 of this series (2001). The present survey covers the literature from mid-1999 to the end of 2013; and in addition to aspects of the isolation, characterization, and biological activity of the alkaloids, much emphasis is placed on their total synthesis. A brief introduction to the topic is followed by an overview of relevant alkaloids from fungal and microbial sources, among them slaframine, cyclizidine, Steptomyces metabolites, and the pantocins. The important iminosugar alkaloids lentiginosine, steviamine, swainsonine, castanospermine, and related hydroxyindolizidines are dealt with in the subsequent section. The fourth and fifth sections cover metabolites from terrestrial plants. Pertinent plant alkaloids bearing alkyl, functionalized alkyl or alkenyl substituents include dendroprimine, anibamine, simple alkaloids belonging to the genera Prosopis, Elaeocarpus, Lycopodium, and Poranthera, and bicyclic alkaloids of the lupin family. Plant alkaloids bearing aryl or heteroaryl substituents include ipalbidine and analogs, secophenanthroindolizidine and secophenanthroquinolizidine alkaloids (among them septicine, julandine, and analogs), ficuseptine, lasubines, and other simple quinolizidines of the Lythraceae, the simple furyl-substituted Nuphar alkaloids, and a mixed quinolizidine-quinazoline alkaloid. The penultimate section of the review deals with the sizable group of simple indolizidine and quinolizidine alkaloids isolated from, or detected in, ants, mites, and terrestrial amphibians, and includes an overview of the "dietary hypothesis" for the origin of the amphibian metabolites. The final section surveys relevant alkaloids from marine sources, and includes clathryimines and analogs, stellettamides, the clavepictines and pictamine, and bis(quinolizidine) alkaloids.

Functional characterization of Sporothrix schenckii glycosidases involved in the N-linked glycosylation pathway

Protein glycosylation pathways are conserved metabolic processes in eukaryotic organisms and are required for cell fitness. In fungal pathogens, the N-linked glycosylation pathway is indispensable for proper cell wall composition and virulence. In Sporothrix schenckii sensu stricto, the causative agent of sporotrichosis, little is known about this glycosylation pathway. Here, using a genome-wide screening for putative members of the glycosyl hydrolase (CAZy - GH) families 47 and 63, which group enzymes involved in the processing step during N-linked glycan maturation, we found seven homologue genes belonging to family 47 and one to family 63. The eight genes were individually expressed in C. albicans null mutants lacking either MNS1 (for members of family 47) or CWH41 (for the member of family 63). Our results indicate that SsCWH41 is the functional ortholog of CaCWH41, whereas SsMNS1 is the functional ortholog of CaMNS1. The remaining genes of family 47 encode Golgi mannosidases and endoplasmic reticulum degradation-enhancing alpha-mannosidase-like proteins (EDEMs). Since these GH families gather proteins used as target for drugs to control cell growth, identification of these genes could help in the design of antifungals that could be used to treat sporotrichosis and other fungal diseases. In addition, to our knowledge, we are the first to report that Golgi mannosidases and EDEMs are expressed and characterized in yeast cells.

Expression of a secretory α-glucosidase II from Apis cerana indica in Pichia pastoris and its characterization

Background

α–glucosidase (HBGase) plays a key role in hydrolyzing α-glucosidic linkages. In Apis mellifera, three isoforms of HBGase (I, II and III) have been reported, which differ in their nucleotide composition, encoding amino acid sequences and enzyme kinetics. Recombinant (r)HBGase II from A. cerana indica (rAciHBGase II) was focused upon here due to the fact it is a native and economic honeybee species in Thailand. The data is compared to the two other isoforms, AciHBGase I and III from the same bee species and to the three isoforms (HBGase I, II and III) in different bee species where available.

Results

The highest transcript expression level of AciHBGase II was found in larvae and pupae, with lower levels in the eggs of A. cerana indica but it was not found in foragers. The full-length AciHBGase II cDNA, and the predicted amino acid sequence it encodes were 1,740 bp and 579 residues, respectively. The cDNA sequence was 90% identical to that from the HBGase II from the closely related A. cerana japonica (GenBank accession # NM_FJ752630.1). The full length cDNA was directionally cloned into the pPICZαA expression vector in frame with a (His)₆ encoding C terminal tag using EcoRI and KpnI compatible ends, and transformed into Pichia pastoris. Maximal expression of the rAciHBGase II–(His)₆ protein was induced by 0.5% (v/v) methanol for 96 h and secreted into the culture media. The partially purified enzyme was found to have optimal α-glucosidase activity at pH 3.5 and 45°C, with > 80% activity between pH 3.5–5.0 and 40–55°C, and was stabile (> 80% activity) at pH 4–8 and at < 25–65°C. The optimal substrate was sucrose.

Conclusions

Like in A. mellifera, there are three isoforms of AciHBGase (I, II and III) that differ in their transcript expression pattern, nucleotide sequences and optimal enzyme conditions and kinetics.