Proteases are essential ingredients in modern laundry detergents. Over the past 30 years, subtilisin proteases employed in the laundry detergent industry have been engineered by directed evolution and rational design to tailor their properties towards industrial demands. This comprehensive review discusses recent success stories in subtilisin protease engineering. Advances in protease engineering for laundry detergents comprise simultaneous improvement of thermal resistance and activity at low temperatures, a rational strategy to modulate pH profiles, and a general hypothesis for how to increase promiscuous activity towards the production of peroxycarboxylic acids as mild bleaching agents. The three protease engineering campaigns presented provide in-depth analysis of protease properties and have identified principles that can be applied to improve or generate enzyme variants for industrial applications beyond laundry detergents.

Ultrahigh throughput screening (uHTS) plays an essential role in directed evolution for tailoring biocatalysts for industrial applications. Flow cytometry-based uHTS provides an efficient coverage of the generated protein sequence space by analysis of up to 107 events per hour. Cell-free enzyme production overcomes the challenge of diversity loss during the transformation of mutant libraries into expression hosts, enables directed evolution of toxic enzymes, and holds the promise to efficiently design enzymes of human or animal origin. The developed uHTS cell-free compartmentalization platform (InVitroFlow) is the first report in which a flow cytometry-based screened system has been combined with compartmentalized cell-free expression for directed cellulase enzyme evolution. InVitroFlow was validated by screening of a random cellulase mutant library employing a novel screening system (based on the substrate fluorescein-di-β-D-cellobioside), and yielded significantly improved cellulase variants (e.g. CelA2-H288F-M1 (N273D/H288F/N468S) with 13.3-fold increased specific activity (220.60 U/mg) compared to CelA2 wildtype: 16.57 U/mg).

Screening throughput is a key in directed evolution experiments and enzyme discovery. Here, we describe a high-throughput screening platform based on a coupled reaction of glucose oxidase and a hydrolase (Yersinia mollaretii phytase [YmPh]). The coupled reaction produces hydroxyl radicals through Fenton's reaction, acting as initiator of poly(ethyleneglycol)-acrylate-based polymerization incorporating a fluorescent monomer. As a consequence, a fluorescent hydrogel is formed around Escherichia coli cells expressing active YmPh. We achieve five times enrichment of active cell population through flow cytometry analysis and sorting of mixed populations. Finally, we validate the performance of the fluorescent polymer shell (fur-shell) technology by directed phytase evolution that yielded improved variants starting from a library containing 10(7) phytase variants. Thus, fur-shell technology represents a rapid and nonlaborious way of identifying the most active variants from vast populations, as well as a platform for generation of polymer-hybrid cells for biobased interactive materials.

Bacillus subtilis strains are used for extracellular expression of enzymes (i.e., proteases, lipases, and cellulases) which are often engineered by directed evolution for industrial applications. B. subtilis DB104 represents an attractive directed evolution host since it has a low proteolytic activity and efficient secretion. B. subtilis DB104 is hampered like many other Bacillus strains by insufficient transformation efficiencies (≤10(3) transformants/μg DNA). After investigating five physical and chemical transformation protocols, a novel natural competent transformation protocol was established for B. subtilis DB104 by optimizing growth conditions and histidine concentration during competence development, implementing an additional incubation step in the competence development phase and a recovery step during the transformation procedure. In addition, the influence of the amount and size of the transformed plasmid DNA on transformation efficiency was investigated. The natural competence protocol is "easy" in handling and allows for the first time to generate large libraries (1.5 × 10(5) transformants/μg plasmid DNA) in B. subtilis DB104 without requiring microgram amounts of DNA.

Understanding interactions between polymers and enzymes to boost enzymatic activity is of high importance for application of enzymes in multicomponent systems, such as laundry, food, pharmaceuticals, or cosmetics. Proteases are widely used in industries and increased performance in the presence of polymers has been reported. Boosting of enzymes activity by polymers and understanding of the molecular principles is of high interest in biomedical and biotechnological applications. A molecular understanding of the boosting effect of poly­(acrylic acid) (PAA) and poly­(l-γ-glutamic acid) (γ-PGA) for a nonspecific subtilisin protease (Protein Database (PDB) ID: 1ST3) was generated through biophysical characterization (fluorescence correlation and circular dichroism spectroscopies, isothermal titration calorimetry), molecular dynamics simulations, and protease reengineering (site-saturation mutagenesis). Our study revealed that enthalpically driven interactions via key amino acid residues close to the protease Ca2+ binding sites cause the boosting effect in protease activity. On the molecular level electrostatic interactions results in the formation of protease-polyelectrolyte complexes. Site-saturation mutagenesis on positions S76, I77, A188, V238, N242, and K245 yielded an increased proteolytic performance against a complex protein mixture (trademark CO-3; up to ∼300% and ∼70%) in the presence of PAA and γ-PGA. Being able to fine-tune interactions between proteins and negatively charged polymers through integrative use of computational design, protein re-engineering and biophysical characterization proved to be an efficient workflow to improve protease performance.