Professor
Department of Chemistry
Krieger School of Arts & Sciences

ctownsend@jhu.edu

252 Remsen Hall
3400 N. Charles Street
Baltimore, MD 21218

Office: 410-516-7444
Lab: 410-516-8441

The research problems in my group range from the heart of organic chemistry to the enzymology and molecular biology of secondary metabolism, mechanisms of drug action and rational drug design. Some specific examples are briefly summarized below.

Every year a portion of the U.S. corn crop is infected with aflatoxins, a family of potent mycotoxins produced by certain strains of the fungus Aspergillus. In our investigations of this toxin great strides have been taken toward making available the key biosynthetic enzymes for more detailed study. From the purified proteins we have been able to localize the corresponding structural genes, over-express these in yeast and E. coli, and examine the organization and control of the enzyme pathway at the genetic level. Prominent among these has been a Type I modular polyketide synthase (PKS), a member of a group of polyfunctional proteins of great current interest for their synthetic power and biotechnological potential. In the past year a pair of specialized Type I fatty acid synthases (FASs) has been characterized that synthesizes a 6-carbon starter unit to initiate polyketide synthesis. Normal fatty acids are C-16 or C-18. The means by with chain length is controlled in these important enzymes is under investigation as is the nature of the quarternary structure of the FAS*PKS complex.

The mechanism of ß-lactam formation is central to the question of how penicillin and related antibiotics are formed. We have cloned the gene clusters that encode the enzymes of these biosynthetic pathways, which has opened the way for detailed investigation of their catalytic properties and structures. Of particular interest are the proteins that carry out ß-lactam synthetase, active in clavulanic acid formation yet entirely distinct from penicillin biosynthesis. A related protein has been found to be active in carbapenem biosynthesis and X-ray structures of both enzymes recently obtained open the way to protein engineering to capture the synthetic power and chiral selection of these enzymes to accept alternate substrates and produce other medicinally-useful products. Similarly, we have just cloned a polypeptide synthetase from the nocardicin producer. As a group, these are giant polydomainal enzymes with remarkable synthetic power and considerable potential for biotechnological application. In this connection we have developed an algorithm to both predict substrates activated, and how one might engineer the amino acid recognition sites that control the identity, stereochemistry and number of amino acid units assembled by these megaproteins.

A new area of research is a collaboration with geneticists, microbiologists, pathologists and oncologists in the School of Medicine on the design, synthesis and testing of selective inhibitors/inactivators of fatty acid synthase (FAS) enzymes. The specific targets fall into two groups: (1) human FAS, which is gigantically up-regulated in cancers of the breast, cervix, prostate, etc., and (2) those lipid elongation enzymes uniquely associated with mycobacteria that cause, e.g., tuberculosis and leprosy. It has been demonstrated that inhibition of these enzymes is an effective, new therapeutic strategy in both human cancers and tuberculosis. TB is a disease that affects one third of the world's population, causes more than 3 million deaths annually and, like all infectious diseases, has become drug-resistant. We have developed a new class of antibiotics effective against TB and MDR-TB with exciting clinical potential and interesting biochemistry to determine its mode of action.

An important and unexpected breakthrough in the understanding of obesity in animals has been made in the last year where FAS inhibition in the hypothalamus and in neurons led to profound weight loss in test animals. Modulation of a metabolic intermediate appears to serve as a sensor molecule whose levels are translated by as yet unknown mechanisms to expression of protein hormones controlling feeding and hunger. Details of these and the research programs above can be found in the publications below.

Selected Publications
Crawford, J.M., B.C.R. Dancy, E.A. Hill, D.W. Udwary, and C.A. Towsend. (2006) Identification of a starter-unit ACP transacylase domain:  First steps in the deconstruction of a type I, iterative polyketide synthase. Proc. Nat. Acad. Sci. USA 103:16728-16733.

Li, R-F., and C.A. Townsend. (2006) Rational strain improvement for enhanced clavulanic acid production by genetic engineering of the glycolytic pathway in Streptomyces clavuligerus. Metabol. Eng. 8:240-252.

Henry, K.M., and C.A. Townsend. (2005) Ordering the reductive and cytochrome P450 oxidative steps in demethylsterigmatocystin formation yields new insights into xanthone biosynthesis. J. Am. Chem. Soc. 127:3724-3733.

McFadden, J.M., S.M. Medghalchi, J.N. Thupari, M.L. Pinn, A. Vadlamudi, K.I. Miller, F.P. Kuhajda, and C.A. Townsend. (2005) Application of a flexible synthesis of (5R)-thiolactomycin to develop new inhibitors of type I fatty acid synthase. J. Med. Chem. 49:946-961.

Kelly, W.L., and C.A. Townsend. (2005) Mutational analysis of nocK and nocL in the nocardicin a producer Nocardia uniformis. J. Bacteriol. 187:739-746.

Gerratana, B., S.O. Arnett, A. Stapon, and C.A. Townsend. (2004) Carboxymethylproline synthase from Pectobacterium carotovora: a multi-faceted member of the crotonase superfamily. Biochemistry 43:15936-15945.

Gunsior, M., S.D. Breazeale, A.J. Lind, J. Ravel, J.W. Janc, and C.A. Townsend. (2004) The biosynthetic gene cluster for a monocyclic ß-lactam antibiotic, nocardicin A. Chem. & Biol. 11:927-938.

Gunsior, M., J. Ravel, G.L. Challis, and C.A. Townsend. (2004) Engineering p-hydroxyphenylpyruvate dioxygenase to a p-hydroxymandelate synthase and evidence for the proposed benzene oxide intermediate in homogentisate formation. Biochemistry 43:663-674.

Stapon, A., R.-F. Li, and C.A. Townsend. (2003) Synthesis of (3S,5R)-carbapenam-3-carboxylic acid and its role in carbapenem biosynthesis and the stereoinversion problem. J. Amer. Chem. Soc. 125:15746-15747.

Gerratana, B., A. Stapon, and C.A. Townsend. (2003) Inhibition and alternate substrate studies on the mechanism of carbapenam synthetase from Erwinia carotovora. Biochemistry 42:7836-7847.

Stapon, A, R.-F. Li, and C.A. Townsend. (2003) Carbapenem biosynthesis: Confirmation of stereochemical assignments and the role of CarC in the ring stereoinversion process from L-proline. J. Amer. Chem. Soc. 125:8486-8493.