Correction: Activity of the Human Rhinovirus 3C Protease Studied in Various Buffers, Additives and Detergents Solutions for Recombinant Protein Production

The Statistical Optimisation of Recombinant β-glucosidase Production through a Two-Stage, Multi-Model, Design of Experiments Approach

β-glucosidases are a class of enzyme that are widely distributed in the living world, with examples noted in plants, fungi, animals and bacteria. They offer both hydrolysis and synthesis capacity for a wide range of biotechnological processes. However, the availability of native, or the production of recombinant β-glucosidases, is currently a bottleneck in the widespread industrial application of this enzyme. In this present work, the production of recombinant β-glucosidase from Streptomyces griseus was optimised using a Design of Experiments strategy, comprising a two-stage, multi-model design. Three screening models were comparatively employed: Fractional Factorial, Plackett-Burman and Definitive Screening Design. Four variables (temperature, incubation time, tryptone, and OD600 nm) were experimentally identified as having statistically significant effects on the production of S.griseus recombinant β-glucosidase in E. coli BL21 (DE3). The four most influential variables were subsequently used to optimise recombinant β-glucosidase production, employing Central Composite Design under Response Surface Methodology. Optimal levels were identified as: OD600 nm, 0.55; temperature, 26 °C; incubation time, 12 h; and tryptone, 15 g/L. This yielded a 2.62-fold increase in recombinant β-glucosidase production, in comparison to the pre-optimised process. Affinity chromatography resulted in homogeneous, purified β-glucosidase that was characterised in terms of pH stability, metal ion compatibility and kinetic rates for p-nitrophenyl-β-D-glucopyranoside (pNPG) and cellobiose catalysis.

Directed evolution of the 3C protease from coxsackievirus using a novel fluorescence-assisted intracellular method

Proteases are crucial for regulating biological processes in organisms through hydrolysis of peptide bonds. Recombinant proteases have moreover become important tools in biotechnological, and biomedical research and as therapeutics. We have developed a label-free high-throughput method for quantitative assessment of proteolytic activity in Escherichia coli. The screening method is based on co-expression of a protease of interest and a reporter complex. This reporter consists of an aggregation-prone peptide fused to a fluorescent protein via a linker that contains the corresponding substrate sequence. Cleavage of the substrate rescues the fluorescent protein from aggregation, resulting in increased fluorescence that correlates to proteolytic activity, which can be monitored using flow cytometry. In one round of flow-cytometric cell sorting, we isolated an efficiently cleaved tobacco etch virus (TEV) substrate from a 1:100 000 background of non-cleavable sequences, with around 6000-fold enrichment. We then engineered the 3C protease from coxsackievirus B3 (CVB3 3Cpro) towards improved proteolytic activity on the substrate LEVLFQ↓GP. We isolated highly proteolytic active variants from a randomly mutated CVB3 3Cpro library with up to 4-fold increase in activity. The method enables simultaneous measurement of proteolytic activity and protease expression levels and can therefore be applied for protease substrate profiling, as well as directed evolution of proteases.