Chemoenzymatic Synthesis of Cryptophycin Anticancer Agents by an Ester Bond-Forming Non-ribosomal Peptide Synthetase Module

Cryptophycins (Crp) are a group of cyanobacterial depsipeptides with activity against drug-resistant tumors. Although they have been shown to be promising, further efforts are required to return these highly potent compounds to the clinic through a new generation of analogues with improved medicinal properties. Herein, we report a chemosynthetic route relying on themultifunctional enzyme CrpD-M2 that incorporates a 2-hydroxy acid moiety (unit D) into Crp analogues. CrpD-M2 is a unique nonribosomal peptide synthetase (NRPS) module comprised of condensation-adenylation-ketoreduction-thiolation (C-A-KR-T) domains. We interrogated A-domain 2-keto and 2-hydroxy acid activation and loading, and KR domain activity in the presence of NADPH and NADH. The resulting 2-hydroxy acid was elongated with three synthetic Crp chain elongation intermediate analogues through ester bond formation catalyzed by CrpD-M2 C domain. Finally, the enzyme-bound seco-Crp products were macrolactonized by the Crp thioesterase. Analysis of these sequential steps was enabled through LC-FTICR-MS of enzyme-bound intermediates and products. This novel chemoenzymatic synthesis of Crp involves four sequential catalytic steps leading to the incorporation of a 2-hydroxy acid moiety in the final chain elongation intermediate. The presented work constitutes the first example where a NRPS-embedded KR domain is employed for assembly of a fully elaborated natural product, and serves as a proof-of-principle for chemoenzymatic synthesis of new Crp analogues

Expanding LAGLIDADG endonuclease scaffold diversity by rapidly surveying evolutionary sequence space

LAGLIDADG homing endonucleases (LHEs) are a family of highly specific DNA endonucleases capable of recognizing target sequences ∼20 bp in length, thus drawing intense interest for their potential academic, biotechnological and clinical applications. Methods for rational design of LHEs to cleave desired target sites are presently limited by a small number of high-quality native LHEs to serve as scaffolds for protein engineering—many are unsatisfactory for gene targeting applications. One strategy to address such limitations is to identify close homologs of existing LHEs possessing superior biophysical or catalytic properties. To test this concept, we searched public sequence databases to identify putative LHE open reading frames homologous to the LHE I-AniI and used a DNA binding and cleavage assay using yeast surface display to rapidly survey a subset of the predicted proteins. These proteins exhibited a range of capacities for surface expression and also displayed locally altered binding and cleavage specificities with a range of in vivo cleavage activities. Of these enzymes, I-HjeMI demonstrated the greatest activity in vivo and was readily crystallizable, allowing a comparative structural analysis. Taken together, our results suggest that even highly homologous LHEs offer a readily accessible resource of related scaffolds that display diverse biochemical properties for biotechnological applications