Flow-cytometric screening of aggregation-inhibitors using a fluorescence-assisted intracellular method

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.

Editorial: Methods and advances for systems and synthetic biology, nanobiotech and medicine

Congratulations to the winners of our cover competition. The first prize goes to the cover of the October issue, which was provided by the authors of the article "Chlorella species as hosts for genetic engineering and expression of heterologous proteins: Progress, challenge and perspective" by Bo Yang, Jin Liu, Yue Jiang and Feng Chen (http://dx.doi.org/10.1002/biot.201500617). Very close by only very few votes followed the July issue cover showing a nice illustration of Aspergillus fungi, which was selected by BTJs Production manager Sigi Mehren and Technical editor Bernadette Gmeiner. The winner of the book voucher was already informed via email. Many thanks to the more than 1000 participants who were voting for these covers!