Prof. David Sherman, "Drug Discovery and Development Efforts Employing Unique Chemical Diversity Resources Against Cardiovascular Targets", Technion Lecture at the University of Michigan Dec. 6, 2012.
Congratulations to Michael M. Kaufman-Schofield for passing her 2nd candidacy checkpoint!
Bolduc, K.L., Larsen, S.D., Sherman, D.H. (2012) Efficient, divergent synthesis of cryptophycin unit A analogues. Chem. Comm. 48, 6414-6416.
Abstract: A flexible and divergent synthesis of cryptophycin unit A analogues is described. This method relies on iridium-catalysed stereo- and enantioselective crotylation and chemoselective one-pot oxidative olefination to access common intermediate 8. Heck, cross metathesis, and Suzuki-Miyaura reactions are illustrated for the generation of methyl ester unit A analogues 10a–d.
Nusca, T.D., Kim, Y., Maltseva, N., Lee, J.Y., Eschenfeldt, W., Stols, L., Schofield, M.M., Scaglione, J.B., Dixon, S.D., Oves-Costales, D., Challis, G.L., Hannah, P.C., Pfleger, B.F., Joachimiak, A., Sherman, D.H. (2012) Functional and structural analysis of the siderophore synthetase AsbB through reconstitution of the petrobactin biosynthetic pathway from Bacillus anthracis. JBC 287, 16058-16072
Abstract: Petrobactin, a mixed catechol-carboxylate siderophore, is required for full virulence of Bacillus anthracis, the causative agent of anthrax. The asbABCDEF operon encodes the biosynthetic machinery for this secondary metabolite. Here, we show that the function of five gene products encoded by the asb operon is necessary and sufficient for conversion of endogenous precursors to petrobactin using an in vitro system. In this pathway, the siderophore synthetase AsbB catalyzes formation of amide bonds crucial for petrobactin assembly through use of biosynthetic intermediates, as opposed to primary metabolites, as carboxylate donors. In solving the crystal structure of the B. anthracis siderophore biosynthesis protein B (AsbB), we disclose a 3-D model of a nonribosomal peptide synthetase (NRPS)-independent siderophore (NIS) synthetase. Structural characteristics provide new insight into how this bifunctional condensing enzyme can bind and adenylate multiple citrate-containing substrates, followed by incorporation of both natural and unnatural polyamine nucleophiles. This activity enables formation of multiple end-stage products leading to final assembly of petrobactin. Subsequent enzymatic assays with the NRPS-like AsbC, AsbD, and AsbE polypeptides show that the alternative products of AsbB are further converted to petrobactin, verifying previously proposed convergent routes to formation of this siderophore. These studies identify potential therapeutic targets to halt deadly infections caused by B. anthracis and other pathogenic bacteria, and suggest new avenues for the chemoenzymatic synthesis of novel compounds.
Chemler, J.A., Buchholz, T.J., Geders, T.W., Akey, D.L., Rath, C.M., Chlipala, G.E., Smith, J.L., Sherman, D.H. (2012) Biochemical and structural charactierzation of germicidin synthase: analysis of a type III polyletide synthase that employs acyl-ACP as a start unit donor. JACS 134, 7359-7366.
Abstract: Germicidin synthase (Gcs) from Streptomyces coelicolor is a type III polyketide synthase (PKS) with broad substrate flexibility for acyl groups linked through a thioester bond to either coenzyme A (CoA) or acyl carrier protein (ACP). Germicidin synthesis was reconstituted in vitro by coupling Gcs with fatty acid biosynthesis. Since Gcs has broad substrate flexibility, we directly compared the kinetic properties of Gcs with both acyl-ACP and acyl-CoA. The catalytic efficiency of Gcs for acyl-ACP was 10-fold higher than for acyl-CoA, suggesting a strong preference toward carrier protein starter unit transfer. The 2.9 Å germicidin synthase crystal structure revealed canonical type III PKS architecture along with an unusual helical bundle of unknown function that appears to extend the dimerization interface. A pair of arginine residues adjacent to the active site affect catalytic activity but not ACP binding. This investigation provides new and surprising information about the interactions between type III PKSs and ACPs that will facilitate the construction of engineered systems for production of novel polyketides.
