 Christian R.H. RaetzGeorge Barth Geller Professor of BiochemistryMembrane biochemistry; biosynthesis of lipid A; endotoxin signaling; antibacterial antibiotics; genomics of lipid diversity. Contact InformationOffice Number: (919) 684-3384 Fax: (919) 684-8885 e-mail raetz@biochem.duke.edu Lab Location Room 239 Nanaline Duke Building Mailing Address Department of Biochemistry 255 Nanaline H. Duke Box 3711, DUMC Durham, NC 27710 Education
Research Interests – SummaryThe biochemistry of phospholipids has been the subject of intense research over the last ten years because of the important roles that these substances play in membrane assembly and signal transduction. Our laboratory has devised high throughput screening assays and expression cloning strategies, applicable to bacteria, yeast and animal cells, for identifying genes encoding enzymes of phospholipid biosynthesis. Using a combination of enzymology, genetics and bioinformatics, we have discovered and assigned the functions of over 20 gene products that are required for generating phospholipid diversity. One of our most intriguing discoveries has been the recognition of a new family of glucosamine-based phospholipids in E. coli. These substances are precursors of lipid A (also known as endotoxin), which makes up the outer monolayer of the outer membrane of E. coli and most other Gram-negative bacteria (Fig 1). Lipid A (Fig 2) not only is required for bacterial growth but also plays an important role in the pathogenesis of infections. Lipid A is an activator of the innate immune system of animals via the receptor TLR-4 (Fig 3) and a potent stimulator of cytokine synthesis in macrophages. In Salmonella, regulated covalent modifications of lipid A play an important role in host-pathogen interactions. Over the past decade, we have discovered ten new enzymes that constitute the pathway for lipid A biosynthesis (Fig 4) in E. coli. We are now exploring the molecular biology and regulation of the lipid A system in bacteria with sequenced genomes. The lipid A pathway is an excellent target for the design of new antibiotics against organisms like E. coli, Salmonella, and Pseudomonas, some of which have become resistant to existing antibiotics. Small molecule inhibitors (Fig 4) of lipid A biosynthesis with antibiotic activity have been identified in our laboratory. The catalytic mechanisms and structural biology (Fig 5) of the enzymes that assemble lipid A are under investigation to facilitate the design of even better inhibitors. Finally, recent bioinformatic observations have led to the remarkable realization that the enzymes of lipid A biosynthesis are not restricted to bacteria, but are also present in plants, where they may generate novel lipid A-like molecules needed as membrane components or in signaling pathways. Selected Publications1. Bartling, C. M. and Raetz, C. R. H. (2009) Crystal structure and acyl chain selectivity of LpxD, the N-acyltransferase of lipid A biosynthesis. Biochemistry 48, 8672-8683. More… 2. Rutten, L., Mannie, J. P., Stead, C. M., Raetz, C. R. H., Reynolds, C. M., Bonvin, A. M., Tommassen, J. P., Egmond, M. R., Trent, M. S., and Gros, P. (2009) Active-site architecture and catalytic mechanism of the lipid A deacylase LpxR of Salmonella typhimurium. Proc. Natl. Acad. Sci. U S A. 106, 1960-1964. More… 3. Ma, B., Reynolds, C. M. and Raetz, C. R. H. (2008) Periplasmic orientation of nascent lipid A in the inner membrane of an Escherichia coli LptA mutant. Proc. Natl. Acad. Sci. USA. 105, 13823-13828. More… 4. Schaaf, G., Ortlund, E. A., Tyeryar, K. R., Mousley, C. J., Ile, K. E., Garrett, T. A., Ren, J., Woolls, M. J., Raetz, C. R. H., Redinbo, M. R. and Bankaitis, V. A. (2008) Functional anatomy of phospholipid binding and regulation of phosphoinositide homeostasis by proteins of the sec14 superfamily. Mol. Cell 29, 191-206. More… 5. Raetz, C. R. H., Reynolds, C. M., Trent, M. S., and Bishop, R. E. (2007) Lipid A modification systems in Gram-negative bacteria. Annu. Rev. Biochem. 76, 295-329. More… 6. Williams, A. H. and Raetz, C. R. H. (2007) Structural basis for the acyl chain selectivity and mechanism of UDP-N-acetylglucosamine acyltransferase. Proc. Natl. Acad. Sci. USA. 104:13543-13550. More… 7. Barb, A. W., Jiang, L., Raetz, C. R. H. and Zhou, P. (2007) Structure of the deacetylase LpxC bound to the antibiotic CHIR-090: Time-dependent inhibition and specificity in ligand binding. Proc Natl Acad Sci U S A. 104:18433-8 More… 8. Wang, X., McGrath, S. C., Cotter, R. J., and Raetz, C. R. H. (2006) Expression cloning and periplasmic orientation of the Francisella novicida lipid A 4’-phosphatase LpxF. J. Biol. Chem. 281, 9321-9330. More… 9. Williams, A. H., Immormino, R. M., Gewirth, D. T., and Raetz, C. R. H. (2006) Structure of UDP-N-acetylglucosamine acyltransferase with a bound antibacterial pentadecapeptide. Proc. Natl. Acad. Sci. USA. 103, 10877-82. More… 10. Gibbons, H. S., Kalb, S. R., Cotter, R. J., and Raetz, C. R. H. (2005) Role of Mg++ and pH in the modification of Salmonella lipid A following endocytosis by macrophage tumor cells. Mol. Microbiol. 55, 425-440. More… 11. Doerrler, W. T. and Raetz, C. R. H. (2005) Loss of outer membrane proteins without inhibition of lipid export in an Escherichia coli YaeT mutant. J. Biol. Chem. 280:27679-87. More… 12. Guan, Z., Breazeale, S. D., and Raetz, C. R. H. (2005) Extraction and identification by mass spectrometry of undecaprenyl diphosphate-MurNAc-pentapeptide-GlcNAc from Escherichia coli. Anal. Biochem. 345, 336-339. More… 13. McClerren, A. L., Endsley, S., Bowman, J. L., Andersen, N. H., Guan, Z. Rudolph, J., and Raetz, C. R. H. (2005) A slow, tight-binding inhibitor of the zinc-dependent deacetylase LpxC of lipid A biosynthesis with antibiotic activity comparable to ciprofloxacin. Biochemistry 44, 16574-16583 More… 14. Wang, X., Karbarz, M. J., McGrath, S. C., Cotter, R. J., and Raetz, C. R. H. (2004) MsbA Transporter-dependent lipid A 1-dephosphorylation on the periplasmic surface of the inner membrane: topography of Francisella novicida LpxE expressed in Escherichia coli. J. Biol. Chem. 279, 49470-49478. More… 15. Doerrler, W. T., Gibbons, H. S., and Raetz, C. R. H. (2004) MsbA-dependent translocation of lipids across the inner membrane of Escherichia coli. J. Biol. Chem. 279, 45102-09. More… 16. Coggins, B. E., Li, X., McClerren, A. L., Hindsgaul, O., Raetz, C. R. H., and Zhou, P. (2003) Structure of the LpxC deacetylase with a bound substrate-analog inhibitor. Nat. Struct. Biol. 10, 645-651. More… 17. Raetz CR, Whitfield C. (2002) Lipopolysaccharide endotoxins. Annu Rev Biochem. 71, 635-700. More… 18. Hwang PM, Choy WY, Lo EI, Chen L, Forman-Kay JD, Raetz CR, Prive GG, Bishop RE, Kay LE. (2002) Solution structure and dynamics of the outer membrane enzyme PagP by NMR. Proc Natl Acad Sci U S A. 99, 13560-5. More… 19. Jackman, J. E., Fierke, C. A., Tumey, L. N., Pirrung, M., Uchiyama, T., Tahir, S. H., Hindsgaul, O., and Raetz, C. R. H. (2000) Antibacterial agents that target lipid A biosynthesis in Gram-negative bacteria: inhibition of diverse UDP-3-O-acyl-N-acetylglucosamine deacetylases by substrate-analogs containing zinc-binding motifs J. Biol. Chem. 275, 11002-11009. More… 20. Wyckoff, T. J. O., Raetz, C. R. H., and Jackman, J. E. (1998) Antibacterial and anti-inflammatory agents that target endotoxin. Trends in Microbiology 6: 154-159. More… 21. Onishi, H. R., Pelak, B. A., Gerckens, L. S., Silver, L. L., Kahan, F. M., Chen, M. H., Patchett, A. A., Galloway, S. M., Hyland, S. A., Anderson, M. S., and Raetz, C. R. H. (1996) Antibacterial agents that inhibit lipid A biosynthesis. Science 274, 980-982. More… 22. Raetz, C. R. H. (1996) Bacterial lipopolysaccharides: a remarkable family of bioactive macroamphiphiles, in Escherichia coli and Salmonella, Vol. I (Neidhardt, F., ed.), Second Edition, pp. 1035-1063, ASM Publications, Washington, DC. More… 23. Raetz, C. R. H. and Roderick, S. L. (1995) A left-handed parallel b-helix in the structure of UDP-N-acetylglucosamine acyltransferase. Science 270, 997-1000. More… |
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