Dr. Craig Townsend
Joint-Appointed Faculty
Professor, Chemistry

Johns Hopkins University
Department of Chemistry
3400 North Charles Street
252 Remsen Hall
Baltimore, MD 21218
410-516-7444 Office
410-516-8420 Fax
ctownsend@jhu.edu
Lab Home Page

The Structure and Function of Complex Biosynthetic Enzymes

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 formation itself. We have recently isolated and characterized a new kind of enzyme, a ß-lactam synthetase, active in clavulanic acid formation yet entirely distinct from penicillin biosynthesis. 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. There is a great need for new and effective antibiotic therapies.

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: