Molecular cloning of the gene encoding β-1,3(4)-glucanase A from a marine bacterium, Pseudomonas sp. PE2, an essential enzyme for the degradation of Pythium porphyrae cell walls

An Aspergillus nidulans endo-β-1,3-glucanase exhibited specific catalytic features and was used to prepare 3-O-β-cellobiosyl-d-glucose and 3-O-β-gentiobiosyl-d-glucose with high antioxidant activity from barley β-glucan and laminarin, respectively

An endo-β-1,3(4)-glucanase AnENG16A from Aspergillus nidulans shows distinctive catalytic features for hydrolysis of β-glucans. AnENG16A hydrolyzed Eisenia bicyclis laminarin to mainly generate 3-O-β-gentiobiosyl-d-glucose and hydrolyzed barley β-glucan to mainly produce 3-O-β-cellobiosyl-d-glucose. Using molecular exclusion chromatography, we isolated and purified 3-O-β-cellobiosyl-d-glucose and 3-O-β-gentiobiosyl-d-glucose, respectively, from AnENG16A-hydrolysate of barley β-glucan and E. bicyclis laminarin. Further study reveals that 3-O-β-cellobiosyl-d-glucose had 8.99-fold higher antioxidant activity than barley β-glucan and 3-O-β-gentiobiosyl-d-glucose exhibited 43.0% higher antioxidant activity than E. bicyclis laminarin. Notably, 3-O-β-cellobiosyl-d-glucose and 3-O-β-gentiobiosyl-d-glucose exhibited 148.9% and 116.0% higher antioxidant activity than laminaritriose, respectively, indicating that β-1,4-linkage or -1,6-linkage at non-reducing end of β-glucotrioses had enhancing effect on antioxidant activity compared to β-1,3-linkage. Furthermore, 3-O-β-cellobiosyl-d-glucose showed 237.9% higher antioxidant activity than cellotriose, and laminarin showed 5.06-fold higher antioxidant activity than barley β-glucan, indicating that β-1,4-linkage at reducing end of β-glucans or oligosaccharides resulted in decrease of antioxidant activity compared to β-1,3-linkage.

Isolation of β-1,3-Glucanase-Producing Microorganisms from Poria cocos Cultivation Soil via Molecular Biology

β-1,3-Glucanase is considered as a useful enzymatic tool for β-1,3-glucan degradation to produce (1→3)-linked β-glucan oligosaccharides with pharmacological activity properties. To validly isolate β-1,3-glucanase-producing microorganisms, the soil of Wolfiporia extensa, considered an environment rich in β-1,3-glucan-degrading microorganisms, was subjected to high throughput sequencing. The results demonstrated that the genera Streptomyces (1.90%) and Arthrobacter (0.78%) belonging to the order Actinomycetales (8.64%) in the phylum Actinobacteria (18.64%) were observed in soil for P. cocos cultivation (FTL₁). Actinomycetes were considered as the candidates for isolation of glucan-degrading microorganisms. Out of 58 isolates, only 11 exhibited β-1,3-glucan-degrading activity. The isolate SYBCQL belonging to the genus Kitasatospora with β-1,3-glucan-degrading activity was found and reported for the first time and the isolate SYBC17 displayed the highest yield (1.02 U/mg) among the isolates. To check the β-1,3-glucanase contribution to β-1,3-glucan-degrading activity, two genes, 17-W and 17-Q, encoding β-1,3-glucanase in SYBC17 and one gene QLK1 in SYBCQL were cloned and expressed for verification at the molecular level. Our findings collectively showed that the isolates able to secrete β-1,3-glucanase could be obtained with the assistance of high-throughput sequencing and genes expression analysis. These methods provided technical support for isolating β-1,3-glucanase-producing microorganisms.

Identification of novel glycosyl hydrolases with cellulolytic activity against crystalline cellulose from metagenomic libraries constructed from bacterial enrichment cultures

To obtain cellulases that are capable of degrading crystalline cellulose and cedar wood, metagenomic libraries were constructed from raw soil sample which was covered to pile of cedar wood sawdust or from its enrichment cultures. The efficiency of screening of metagenomic library was improved more than 3 times by repeating enrichment cultivation using crystalline cellulose as a carbon source, compared with the library constructed from raw soil. Four cellulase genes were obtained from the metagenomic libraries that were constructed from the total genome extracted from an enrichment culture that used crystalline cellulose as a carbon source. A cellulase gene and a xylanase gene were obtained from the enrichment culture that used unbleached kraft pulp as a carbon source. The culture supernatants of Escherichia coli expressing three clones that were derived from the enrichment culture that used crystalline cellulose showed activity against crystalline cellulose. In addition, these three enzyme solutions generated a reducing sugar from cedar wood powder. From these results, the construction of a metagenomic library from cultures that were repetition enriched using crystalline cellulose demonstrated that this technique is a powerful tool for obtaining cellulases that have activity toward crystalline cellulose.

Discovery and characterization of a distinctive exo-1,3/1,4-{beta}-glucanase from the marine bacterium Pseudoalteromonas sp. strain BB1

Marine bacteria residing on local red, green, and brown seaweeds were screened for exo-1,3-β-glucanase (ExoP) activity. Of the 90 bacterial species isolated from 32 seaweeds, only one, a Pseudoalteromonas sp., was found to display such activity. It was isolated from a Durvillaea sp., a brown kelp known to contain significant amounts of the storage polysaccharide laminarin (1,3-β-D-glucan with some 1,6-β branching). Four chromatographic steps were utilized to purify the enzyme (ExoP). Chymotryptic digestion provided peptide sequences for primer design and subsequent gene cloning. The exoP gene coded for 840 amino acids and was located just 50 bp downstream from a putative lichenase (endo-1,3-1,4-β-glucanase) gene, suggesting possible cotranscription of these genes. Sequence comparisons revealed ExoP to be clustered within a group of bacterial glycosidases with high similarity to a group of glycoside hydrolase (GH3) plant enzymes, of which the barley exo-1,3/1,4-β-glucanase (ExoI) is the best characterized. The major difference between the bacterial and plant proteins is an extra 200- to 220-amino-acid extension at the C terminus of the former. This additional sequence does not correlate with any known functional domain, but ExoP was not active against laminarin when this region was removed. Production of recombinant ExoP allowed substrate specificity studies to be performed. The enzyme was found to possess similar levels of exoglucanase activity against both 1,4-β linkages and 1,3-β linkages, and so ExoP is designated an exo-1,3/1,4-β-exoglucanase, the first such bacterial enzyme to be characterized. This broader specificity could allow the enzyme to assist in digesting both cell wall cellulose and cytoplasmic laminarin.

The family 6 carbohydrate-binding modules have coevolved with their appended catalytic modules toward similar substrate specificity

The survey of carbohydrate active enzymes in genomic data uncovered the modular architecture of most of these proteins. Many of the additional modules associated with catalytic modules tightly bind carbohydrates. The primary role of these carbohydrate-binding modules (CBMs) is to enhance the enzymatic activity of the ensemble by bringing their appended catalytic module(s) in intimate contact with their substrates. Biochemical and biophysical approaches have unraveled the subtle interplay of the modules and the structural basis for their ligand specificities, but little attention has been paid to the evolutionary mechanisms leading to the appearance of modular architecture in carbohydrate active enzymes. Focusing on the promiscuous family CBM6 modules, we investigated the evolution of substrate specificities in parallel to that of their respectively appended catalytic modules. An extensive phylogenetic analysis of family CBM6 modules indicates that these noncatalytic modules have diverged into clades which coincide with their substrate selectivity. These data as well as the remarkable congruence of the phylogenetic trees inferred from CBM6s on the one hand and their associated catalytic modules on the other hand show that CBM6s and their associated glycoside hydrolases have coevolved to acquire the same substrate specificity. We also propose an evolutionary scenario explaining the emergence of the modular agarases, by which existent alpha-agarases acquired their agar-binding CBM6 module through a lateral transfer from pre-existing beta-agarases. Altogether, this observed coevolution between CBM6s and their catalytic modules will facilitate the prediction of the substrate specificity of uncharacterized CBM6 modules present in genomic data.

Flavobacterium sp. strain 4221 and Pedobacter sp. strain 4236 beta-1,3-glucanases that are active at low temperatures

Secretion of beta-1,3-glucanases by the arctic bacterial isolates 4221 and 4236, related to the genera Flavobacterium and Pedobacter, was discovered. Escherichia coli and Lactococcus lactis expression of beta-1,3-glucanases Glc4221-1 and Glc4236-1 from the respective isolates was achieved. The enzymes hydrolyzed fungal cell walls and retained activity at low temperatures.

Novel modular enzymes encoded by a cellulase gene cluster in Cellvibrio mixtus

Hydrolysis of plant cell wall polysaccharides, a process which is of intrinsic biological and biotechnological importance, requires the concerted action of an extensive repertoire of microbial cellulases and hemicellulases. Here, we report the identification of the gene cluster unk16A, regA and cel5B in the aerobic soil bacterium Cellvibrio mixtus, encoding a family 16 (CmUnk16A) glycoside hydrolase (GH), an AraC/XylS transcription activator (CmRegA) and a family 5 (CmCel5B) endo-glucanase, respectively. CmUnk16A is a modular enzyme comprising, in addition to the catalytic domain, two family 32 carbohydrate-binding modules (CBMs), termed CBM32-1 and CBM32-2, a CBM4 and a domain of unknown function. We show that CBM32-2 binds weakly to laminarin and pustulan. CmRegA is also a modular protein containing a highly hydrophobic N-terminal domain and a C-terminal DNA-binding domain of the AraC/XylS family. The role of the identified enzymes in the hydrolysis of cell wall polysaccharides by aerobic bacteria is discussed.