Genetic optimization of biotin-binding proteins : artificial metalloenzymes and beyond

Abstract

The versatility of the biotin-(strept)avidin system has been exploited as important tool in a plethora of medical and biotechnological applications, including molecular detection, immobilization, protein purification, construction of supramolecular assemblies and artificial metalloenzymes. The incorporation of catalytically active biotinylated complexes within streptavidin affords artificial transfer hydrogenases for the reduction of prochiral ketones. Genetic “fine-tuning” of the second coordination sphere through a “designed” evolution scheme improves the fitness of hybrid catalysts in terms of enantioselectivity and catalytic performance. High throughput screening strategies allow the identification of highly selective scaffolds for the reduction of challenging substrates, such as dialkyl ketones. The well-tailored streptavidin binding pocket can also accommodate biotinylated metallodrugs such as ruthenium piano stool complexes. The resulting metallodrug-presenter protein assemblies modulate specific DNA recognition patterns through additional non-covalent interactions. Chemo-genetic modifications, by varying the complex or mutating the protein, modulate binding to different DNA targets. The recombinant expression and characterization of a novel secreted biotin-binding protein from the human pathogen B. pseudomallei, named burkavidin, reveals strong biotin-binding activity and high stability as attractive properties for its use as artificial metalloenzyme. In combination with a biotinylated metal complex burkavidin performs the enantioselective hydrogenation of N-protected dehydroamino acids. Recombinantly expressed into the periplasm of E. coli cells, burkavidin represents a milestone for in vivo catalysis as the creation of hybrid enzymes within the cell periplasm may allow catalytic reactions to be carried out in vivo.