Reassembly of enzymes from peptide fragments has been used as a strategy for understanding the evolution, folding, and role of individual subdomains in catalysis and regulation of activity. We demonstrate an oligomerization-assisted enzyme reassembly strategy whereby fragments are covalently linked to independently folding and interacting domains whose interactions serve to promote efficient refolding and complementation of fragments, forming active enzyme. We show that active murine dihydrofolate reductase (E.C. 1.5.1.3) can be reassembled from complementary N-and C-terminal fragments when fused to homodimerizing GCN4 leucine zipper-forming sequences as well as heterodimerizing protein partners. Reassembly is detected by an in vivo selection assay in Escherichia coli and in vitro. The effects of mutations that disrupt fragment affinity or enzyme activity were assessed. The steady-state kinetic parameters for the reassembled mutant (Phe-31 3 Ser) were determined; they are not significantly different from the full-length mutant. The strategy described here provides a general approach for protein dissection and domain swapping studies, with the capacity both for rapid in vivo screening as well as in vitro characterization. Further, the strategy suggests a simple in vivo enzyme-based detection system for protein-protein interactions, which we illustrate with two examples: ras-GTPase and raf-ras-binding domain and FK506-binding proteinrapamycin complexed with the target of rapamycin TOR2.

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This critical review presents an introduction to biocatalysis for synthetic chemists. Advances in biocatalysis of the past 5 years illustrate the breadth of applications for these powerful and selective catalysts in conducting key reaction steps. Asymmetric synthesis of value-added targets and other reaction types are covered, with an emphasis on pharmaceutical intermediates and bulk chemicals. Resources of interest for the non-initiated are provided, including specialized websites and service providers to facilitate identification of suitable biocatalysts, as well as references to recent volumes and reviews for more detailed biocatalytic procedures. Challenges related to the application of biocatalysts are discussed, including how 'green' a biocatalytic reaction may be, and trends in biocatalyst improvement through enzyme engineering are presented (152 references).