Tuberculosis is the world's leading cause of death from a single infectious agent. The emergence of multidrug resistance tuberculosis poses a major new threat to the public health, giving new urgency to research aimed at combating this ancient scourge. The development of new strategies to prevent and treat tuberculosis requires more basic knowledge about the key molecules of the organism that allow it to infect the host. One such key molecule is glutamine synthetase. M. tuberculosis glutamine synthetase has three remarkable and very important characteristics, all discovered in the investigator's laboratory during the past three years. First, it is one of the major extracellular proteins and its export by the bacterium is highly correlated with pathogenicity, i.e., pathogenic mycobacteria secrete the enzyme but nonpathogenic mycobacteria do not. Second, its export, which does not involve a signal peptide, is determined by its amino acid sequence, making it an ideal model protein for studying signal peptide-independent protein export. Third, inhibition of its extracellular enzyme activity inhibits its growth both in broth and within human macrophages, making it an extraordinarily accessible and promising target for new antibiotic development. This project has two major goals. First, the investigators seek to use molecular biological approaches to map which amino acids govern the export of M. tuberculosis glutamine synthetase. Second, building upon their studies of a parent compound that inhibits the glutamine synthetase activity and growth of M. tuberculosis and upon their collaborative studies of the high resolution 3-dimensional structure of M. tuberculosis glutamine synthetase, they hope to develop more active entities than the parent compound and thereby to develop a new antibiotic against M. tuberculosis.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
Project #
Application #
Study Section
Bacteriology and Mycology Subcommittee 2 (BM)
Program Officer
Sizemore, Christine F
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California Los Angeles
Internal Medicine/Medicine
Schools of Medicine
Los Angeles
United States
Zip Code
Harth, Gunter; Horwitz, Marcus A (2003) Inhibition of Mycobacterium tuberculosis glutamine synthetase as a novel antibiotic strategy against tuberculosis: demonstration of efficacy in vivo. Infect Immun 71:456-64
Tullius, Michael V; Harth, Gunter; Horwitz, Marcus A (2003) Glutamine synthetase GlnA1 is essential for growth of Mycobacterium tuberculosis in human THP-1 macrophages and guinea pigs. Infect Immun 71:3927-36
Harth, Gunter; Horwitz, Marcus A; Tabatadze, David et al. (2002) Targeting the Mycobacterium tuberculosis 30/32-kDa mycolyl transferase complex as a therapeutic strategy against tuberculosis: Proof of principle by using antisense technology. Proc Natl Acad Sci U S A 99:15614-9
Tullius, M V; Harth, G; Horwitz, M A (2001) High extracellular levels of Mycobacterium tuberculosis glutamine synthetase and superoxide dismutase in actively growing cultures are due to high expression and extracellular stability rather than to a protein-specific export mechanism. Infect Immun 69:6348-63
Harth, G; Zamecnik, P C; Tang, J Y et al. (2000) Treatment of Mycobacterium tuberculosis with antisense oligonucleotides to glutamine synthetase mRNA inhibits glutamine synthetase activity, formation of the poly-L-glutamate/glutamine cell wall structure, and bacterial replication. Proc Natl Acad Sci U S A 97:418-23
Harth, G; Horwitz, M A (1999) Export of recombinant Mycobacterium tuberculosis superoxide dismutase is dependent upon both information in the protein and mycobacterial export machinery. A model for studying export of leaderless proteins by pathogenic mycobacteria. J Biol Chem 274:4281-92
Harth, G; Horwitz, M A (1999) An inhibitor of exported Mycobacterium tuberculosis glutamine synthetase selectively blocks the growth of pathogenic mycobacteria in axenic culture and in human monocytes: extracellular proteins as potential novel drug targets. J Exp Med 189:1425-36