Expression, purification, and characterization of recombinant Metarhizium anisopliae acid trehalase in Pichia pastoris

The many functions of carbohydrate-active enzymes in family GH65: diversity and application

Glycoside Hydrolase family 65 (GH65) is a unique family of carbohydrate-active enzymes. It is the first protein family to bring together glycoside hydrolases, glycoside phosphorylases and glycosyltransferases, thereby spanning a broad range of reaction types. These enzymes catalyze the hydrolysis, reversible phosphorolysis or synthesis of various α-glucosides, typically α-glucobioses or their derivatives. In this review, we present a comprehensive overview of the diverse reaction types and substrate specificities found in family GH65. We describe the determinants that control this remarkable diversity, as well as the applications of GH65 enzymes for carbohydrate synthesis.

Structure of a bacterial α-1,2-glucosidase defines mechanisms of hydrolysis and substrate specificity in GH65 family hydrolases

Glycoside hydrolase family 65 (GH65) comprises glycoside hydrolases (GHs) and glycoside phosphorylases (GPs) that act on α-glucosidic linkages in oligosaccharides. All previously reported bacterial GH65 enzymes are GPs, whereas all eukaryotic GH65 enzymes known are GHs. In addition, to date, no crystal structure of a GH65 GH has yet been reported. In this study, we use biochemical experiments and X-ray crystallography to examine the function and structure of a GH65 enzyme from Flavobacterium johnsoniae (FjGH65A) that shows low amino acid sequence homology to reported GH65 enzymes. We found that FjGH65A does not exhibit phosphorolytic activity, but it does hydrolyze kojibiose (α-1,2-glucobiose) and oligosaccharides containing a kojibiosyl moiety without requiring inorganic phosphate. In addition, stereochemical analysis demonstrated that FjGH65A catalyzes this hydrolytic reaction via an anomer-inverting mechanism. The three-dimensional structures of FjGH65A in native form and in complex with glucose were determined at resolutions of 1.54 and 1.40 Å resolutions, respectively. The overall structure of FjGH65A resembled those of other GH65 GPs, and the general acid catalyst Glu⁴⁷² was conserved. However, the amino acid sequence forming the phosphate-binding site typical of GH65 GPs was not conserved in FjGH65A. Moreover, FjGH65A had the general base catalyst Glu⁶¹⁶ instead, which is required to activate a nucleophilic water molecule. These results indicate that FjGH65A is an α-1,2-glucosidase and is the first bacterial GH found in the GH65 family.

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.

A eukaryotic expression strategy for producing the novel antimicrobial peptide PRW4

The antimicrobial peptide PMAP-36 is a cationic peptide derived from porcine myeloid. The N-terminally paired lysine of PMAP-36 was substituted with tryptophan, and the C-terminal hydrophobic tail was deleted, thereby obtaining the antimicrobial peptide PRW4. PRW4 is a α-helical antimicrobial peptide with broad-spectrum antimicrobial activity. In this study, PRW4 was fused to the 6× His-Trx, and the fusion protein was successfully expressed in Pichia pastoris GS115 from the vector pPICZαA. The maximal induction of recombinant protein occurred in the presence of 1% methanol after 96 h at pH 6.0. After purification by a Ni-NTA resin column and digestion by enterokinase protease, 15 mg of recombinant PRW4 with a purity of 90% was obtained from 1 L of fermentation culture. The results indicated that recombinant PRW4 had similar antimicrobial activity as synthetic PRW4 against bacteria such as Escherichia coli ATCC 25922, Escherichia coli UB 1005, Salmonella typhimurium C7731, Salmonella typhimurium 7913, Salmonella typhimurium ATCC 14028, Staphylococcus aureus ATCC 29213, Staphylococcus epidermidis ATCC 12228, and Streptococcus faecalis ATCC 29212. We have successfully expressed PRW4 in P. pastoris, and this work provides a reference for the production of modified antimicrobial peptides in P. pastoris.

High-level expression of highly active and thermostable trehalase from Myceliophthora thermophila in Aspergillus niger by using the CRISPR/Cas9 tool and its application in ethanol fermentation

Trehalase catalyzes the hydrolysis of the non-reducing disaccharide trehalose. The highly active trehalase MthT from Myceliophthora thermophila was screened from the trehalase genes of six species of filamentous fungi. An ingenious multi-copy knock-in expression strategy mediated by the CRISPR/Cas9 tool and medium optimization were used to improve MthT production in Aspergillus niger, up to 1698.83 U/mL. The protein background was dramatically abated due to insertion. The recombinant MthT showed optimal activity at pH 5.5 and 60 °C, and exhibited prominent thermal stability between 50 and 60 °C under acid conditions (pH 4.5-6.5). The ethanol conversion rate (ethanol yield/total glucose) was significantly improved by addition of MthT (51.88%) compared with MthT absence (34.38%), using 30% starch saccharification liquid. The results of this study provided an effective strategy, established a convenient platform for heterologous expression in A. niger and showed a potential strategy to decrease production costs in industrial ethanol production.

High cell density fed-batch production of insecticidal recombinant ribotoxin hirsutellin A from Pichia pastoris

BACKGROUND

The fungal ribotoxin hirsutellin A (HtA) exhibits strong insecticidal activity; however, efficient systems for expressing recombinant HtA (rHtA) are lacking. Here, we established an efficient heterologous expression system to produce large amounts of rHtA.

RESULTS

Recombinant Pichia pastoris transformants with high levels of secretory rHtA were screened, and in a fed-batch reactor, rHtA was secreted at levels up to 80 mg/l following methanol induction, which was more than sixfold higher than that in shake flasks. Approximately 7 mg of highly pure rHtA was obtained from 300 ml of fed-batch culture supernatant by Ni+-nitriloacetic acid affinity chromatography and CM Sepharose ion-exchange chromatography. Mass spectrometry results revealed rHtA as a native N-terminal non-glycosylated monomeric protein with a molecular weight of 15.3 kDa. Purified rHtA exhibited excellent thermal and protease stability and dose-dependent cytotoxicity to Sf9 insect cells and insecticidal activity against Galleria mellonella larvae.

CONCLUSIONS

This is the first report of rHtA expression in P. pastoris. The rHtA was expressed at a high level under high-cell-density fed-batch fermentation and was efficiently purified using a two-step purification method. Purified rHtA exhibited thermal and protease stability, as well as appropriate bioactivities. Our results indicate that fed-batch production by P. pastoris is an efficient method to produce functional rHtA.

Improving the secretory expression of active recombinant AaIT in Pichia pastoris by changing the expression strain and plasmid

Scorpion long-chain insect selective neurotoxin AaIT has the potential to be used against agricultural insect pests. However, there is still a lack of a heterologous gene expression system that can express AaIT efficiently. Here, using X33 as the host strain and pPICZαA as the expression vector, one transformant had the highest expression of recombinant AaIT (rAaIT) was obtained, and secreted as high as 240 mg/l rAaIT in fed-batch fermentation. Secretory rAaIT was purified by Ni²⁺-nitriloacetic affinity and CM chromatography, and 8 mg of high purity rAaIT were purified from 200 ml fed-batch fermentation cultures. Injecting silkworm (Bombyx mori Linnaeus) and Galleria mellonella larvae with rAaIT resulted in obvious neurotoxin symptoms and led to death. These results demonstrate that a large amount of anti-insect active rAaIT could be prepared efficiently.

Expression, purification, and analyses of glycosylation and disulfide bonds of Stereum purpureum endopolygalacturonase I in Pichia pastoris

We have succeeded in the expression of Stereum purpureum endopolygalacturonase I (EndoPG I) using the Pichia expression system and in purification of the three kinds of recombinant EndoPG I, which have one to three sugar chains by using CM52 column chromatography. The sugar chains which were added to EndoPG I were the M8, M9, and/or M10 high-mannose type. The results of LC-MS analysis showed that recombinant EndoPG Is were randomly glycosylated at four N-glycosylation sites. From the thermal denaturation curves of the recombinant enzymes, it was suggested that EndoPG I differing in thermal stability was included in the sample after purification. Therefore, we investigated the disulfide bonds of recombinant EndoPG I by LC-MS analysis. As a result, peptides without a second or third disulfide bond were detected. This result is the first indicating that there are incomplete enzymes in terms of disulfide bonds in the Pichia expression system.