Effect of Pichia pastoris host strain on the properties of recombinant Aspergillus niger endoglucanase, EglB

Aims@#The methylotrophic yeast Pichia pastoris is widely used to express foreign proteins fused to secretion signals. As the effect of the expression host on the final protein product is unclear, we compared the properties of an endoglucanase (eglB of Aspergillus niger) expressed in two different P. pastoris strains. @*Methodology and results@#Full-length cDNA encoding endoglucanase of A. niger strain ATCC10574 was isolated and expressed in P. pastoris X33 (the methanol utilisation plus phenotype, Mut+) and P. pastoris GS115 (slow methanol utilisation, MutS). EglB-GS115 showed the highest activity and stability at 60 °C while EglB-X33 was most active at 50 °C. EglB-X33 was active towards other substrates such as arabinogalactan, guar gum and locust bean gum besides its specific substrate, carboxymethyl cellulose (CMC). However, EglB-GS115 was only active on CMC. The affinity of EglB-X33 towards CMC (Km = 7.5 mg/mL and specific activity 658 U/mg) was higher than that of EglB-GS115 (Km = 11.57 mg/mL, specific activity 144 U/mg). @*Conclusion, significance and impact of study@#Although eglB was cloned in the same expression vector (pPICZαC), two different characteristics of enzymes were recovered from the supernatant of the different hosts. Thus, expression of recombinant enzyme in different P. pastoris strains greatly affects the physical structure and biochemical properties of the enzyme.

Short-chain fructo-oligosaccharides produced by enzymatic hydrolysis enhance the growth of probiotics isolated from cultured milk drinks

Aims@#Short-chain fructo-oligosaccharides (scFOSs) are good prebiotics that enhance the growth of probiotic bacteria. The aim of this study is to determine the effect of scFOSs produced by levan hydrolysis using recombinant endo-levanase from B. lehensis G1 on the growth of probiotics isolated from commercially cultured milk drinks. @*Methodology and results@#Two probiotic bacteria, Lactobacillus casei and L. rhamnosus, were isolated from commercially cultured milk drinks. ScFOSs were produced by levan hydrolysis using recombinant endo-levanase from B. lehensis G1. The scFOS and levan (control) were added independently to the growth medium, and the growth rates of the probiotic bacteria were determined. Results showed that the growth rate of L. casei decreased in the presence of levan compared with the control medium but increased by approximately 20% when supplemented with scFOS produced by Levblg1-N28S. Similarly, the growth rate of L. rhamnosus increased by approximately 20% when supplemented with scFOS produced by Levblg1 and Levblg1-N28S. @*Conclusion, significance and impact of study@#The scFOSs produced by the enzymatic hydrolysis of levan using a recombinant endo-levanase from B. lehensis G1 have significant potential as prebiotics because they were able to promote the growth of the probiotic bacteria.

Gene isolation and prediction of the corresponding three-dimensional structure of subtilisin from the psychrophilic yeast, Glaciozyma antarctica PI12

Aims@#Subtilisin, a serine protease, is a key player in many industrial applications especially in the detergent industry. Most reported subtilisins originate from mesophilic and thermophilic microorganisms. Only scarce information about cold-active subtilisins from psychrophilic microbes is available. Here we describe the isolation, cloning and in silico characterisation of a gene encoding subtilisin in the obligate psychrophilic yeast, Glaciozyma antarctica PI12. @*Methodology and results@#A full-length cDNA from Glaciozyma antarctica encoding subtilisin (GaSUB) was isolated through Reverse-Transcription-Polymerase Chain Reaction (RT-PCR) techniques. The open reading frame of GaSUB comprised 1,125 nucleotides encoding 375 amino acids. The GaSUB amino acid sequence had 49% sequence identity with a subtilisin from the yeast, Puccinia striiformis. Bioinformatic analyses revealed that the GaSUB protein contains a domain that represents the S8 domain of the largest protease family. The predicted model of GaSUB protein using MODELLER and Pymol software revealed that this enzyme has longer loops and less intramolecular interactions between amino acid residues as compared to its mesophilic and thermophilic counterparts. These characteristics are known to help in protein flexibility and stability in cold-active enzymes. @*Conclusion, significance and impact of study@#Bioinformatics characterisations suggested that this enzyme is uniquely adapted to cold environments. Further work using amplified cDNA will be conducted to confirm the catalytic function of this enzyme.