Genetic and Structural Characterization of a Thermo-Tolerant, Cold-Active, and Acidic Endo-ß-1,4-glucanase from Antarctic Springtail, Cryptopygus antarcticus.

The CaCel gene from Antarctic springtail Cryptopygus antarcticus codes for a cellulase belonging to the glycosyl hydrolase family 45 (GHF45). Phylogenetic, biochemical, and structural analyses revealed that the CaCel gene product (CaCel) is closely related to fungal GHF45 endo-ß-1,4-glucanases. The organization of five introns within the open reading frame of the CaCel gene indicates its endogenous origin in the genome of the species, which suggests the horizontal transfer of the gene from fungi to the springtail. CaCel exhibited optimal activity at pH 3.5, retained 80% of its activity at 0-10 °C, and maintained a half-life of 4 h at 70 °C. Based on the structural comparison between CaCel and a fungal homologue, we deduced the structural basis for the unusual characteristics of CaCel. Under acidic conditions at 50 °C, CaCel was effective to digest the green algae (Ulva pertusa), suggesting that it could be exploited for biofuel production from seaweeds.

Morphological, molecular, and biochemical characterization of astaxanthin-producing green microalga Haematococcus sp. KORDI03 (Haematococcaceae, Chlorophyta) isolated from Korea.

A unicellular red microalga was isolated from environmental freshwater in Korea, and its morphological, molecular, and biochemical properties were characterized. Morphological analysis revealed that the isolate was a unicellular biflagellated green microalga that formed a non-motile, thick-walled palmelloid or red aplanospore. To determine the taxonomical position of the isolate, its 18S rRNA and rbcL genes were sequenced and phylogenetic analysis was performed. We found that the isolate was clustered together with other related Haematococcus strains showing differences in the rbcL gene. Therefore, the isolated microalga was classified into the genus Haematococcus, and finally designated Haematococcus sp. KORDI03. The microalga could be cultivated in various culture media under a broad range of pH and temperature conditions. Compositions of the microalgal cellular components were analyzed, and its protein, carbohydrate, and lipid compositions were estimated to be 21.1 ± 0.2%, 48.8 ± 1.8%, and 22.2 ± 0.9%, respectively. In addition, D-glucose and D-mannose were the dominant monosaccharides in the isolate, and its amino acids were composed mainly of aspartic acid, glutamic acid, alanine, and leucine. Moreover, several polyunsaturated fatty acids accounted for about 80% of the total fatty acids in Haematococcus sp. KORDI03, and the astaxanthin content in the red aplanospores was estimated to be 1.8% of the dry cell weight. To the best of our knowledge, this is the first report of an Haematococcus sp. isolated from Korea, which may be used for bioresource production in the microalgal industry.

Structure-based investigation into the functional roles of the extended loop and substrate-recognition sites in an endo-ß-1,4-D-mannanase from the Antarctic springtail, Cryptopygus antarcticus.

Endo-ß-1,4-D-mannanase from the Antarctic springtail, Cryptopygus antarcticus (CaMan), is a cold-adapted ß-mannanase that has the lowest optimum temperature (30°C) of all known ß-mannanases. Here, we report the apo- and mannopentaose (M5) complex structures of CaMan. Structural comparison of CaMan with other ß-mannanases from the multicellular animals reveals that CaMan has an extended loop that alters topography of the active site. Structural and mutational analyses suggest that this extended loop is linked to the cold-adapted enzymatic activity. From the CaMan-M5 complex structure, we defined the mannose-recognition subsites and observed unreported M5 binding site on the surface of CaMan.

Characterization of Cryptopygus antarcticus endo-ß-1,4-glucanase from Bombyx mori expression systems.

Endo-ß-1,4-glucanase (CaCel) from Antarctic springtail, Cryptopygus antarcticus, a cellulase with high activity at low temperature, shows potential industrial use. To obtain sufficient active cellulase for characterization, CaCel gene was expressed in Bombyx mori-baculovirus expression systems. Recombinant CaCel (rCaCel) has been expressed in Escherichia coli (Ec-CaCel) at temperatures below 10°C, but the expression yield was low. Here, rCaCel with a silkworm secretion signal (Bm-CaCel) was successfully expressed and secreted into pupal hemolymph and purified to near 90% purity by Ni-affinity chromatography. The yield and specific activity of rCaCel purified from B. mori were estimated at 31 mg/l and 43.2 U/mg, respectively, which is significantly higher than the CaCel yield obtained from E. coli (0.46 mg/l and 35.8 U/mg). The optimal pH and temperature for the rCaCels purified from E. coli and B. mori were 3.5 and 50°C. Both rCaCels were active at a broad range of pH values and temperatures, and retained more than 30% of their maximal activity at 0°C. Oligosaccharide structural analysis revealed that Bm-CaCel contains elaborated N- and O-linked glycans, whereas Ec-CaCel contains putative O-linked glycans. Thermostability of Bm-CaCel from B. mori at 60°C was higher than that from E. coli, probably due to glycosylation.

Expression at 279†K, purification, crystallization and preliminary X-ray crystallographic analysis of a novel cold-active ß-1,4-D-mannanase from the Antarctic springtail Cryptopygus antarcticus.

The CaMan gene product from Cryptopygus antarcticus, which belongs to the glycoside hydrolase family 5 type ß-1,4-D-mannanases, has been crystallized using a precipitant solution consisting of 0.1 M Tris-HCl pH 8.5, 25%(w/v) polyethylene glycol 3350 by the microbatch crystallization method at 295 K. The CaMan protein crystal belonged to space group P212121, with unit-cell parameters a = 73.40, b = 83.81, c = 163.55 Å. Assuming the presence of two molecules in the asymmetric unit, the solvent content was estimated to be about 61.29%. CaMan-mannopentaose (M5) complex crystals that were isomorphous to the CaMan crystals were obtained using the same mother liquor containing 1 mM M5.

Cultivation at 6-10°C is an effective strategy to overcome the insolubility of recombinant proteins in Escherichia coli.

Protein expression in Escherichia coli at 15-25°C is widely used to increase the solubility of recombinant proteins. However, many recombinant proteins are insolubly expressed even at those low temperatures. Here, we show that recombinant proteins can be expressed as soluble forms by simply lowering temperature to 6-10°C without cold adapted chaperon systems. By using E. coli Rosetta-gami2(DE3), we obtained 1.8 and 0.9mg of Cryptopygus antarticus mannanase (CaMan) and cellulase (CaCel) from 1l culture grown at 6 and 10°C, respectively. Cultivation at 10°C also led to successful expression of EM3L7 (a lipase isolated from a metagenomic library) in a soluble form in E. coli BL21(DE3). Consequently, E. coli cultivation at 6-10°C is an effective strategy for overcoming a major hurdle of the inclusion body formation.

Molecular and biochemical characterizations of a novel arthropod endo-beta-1,3-glucanase from the Antarctic springtail, Cryptopygus antarcticus, horizontally acquired from bacteria.

Collembolan species have been known to have beta-1,3-glucanase activity and yet the genes coding such enzymes have not been demonstrated. We report here a novel arthropod endo-beta-1,3-glucanase gene CaLam from the Antarctic springtail, Cryptopygus antarcticus. The open reading frame consists of 813bp encoding 270 amino acids with a putative signal peptide and a typical motif of glycosyl hydrolase family 16 (GHF16), E-I-D-I-T-E. The recombinant protein expressed in E. coli shows the hydrolytic activity toward laminarin (K(m) approximately 9.98mg/mL) with an optimal temperature 50 degrees C and an optimal pH 6.0. CaLam digests laminarin and laminarioligosaccharides except laminaribiose as an endo-beta-1,3-glucanase, releasing glucose, laminaribiose and laminaritriose as the major products. Analyses of molecular phylogeny of CaLam and its protein structure reveal that CaLam is closely related with bacterial beta-1,3-glucanases more than with the eukaryotic homologues. Even so, the genomic structure of the CaLam gene consisting of six exons interspersed with approximately 57 to 63bp introns confirms that it is endogenous in the genome of the Antarctic springtail. These results suggest that CaLam should have been transferred from bacteria to the lineage of the Collembolan species by horizontal gene transfer.