Faculty: R. Pad Padmanabhan


Dr. Padmanabhan is Professor of Microbiology & Immunology

Summary:

  • Ph.D. Wayne State University, Detroit, MI., 1968
  • Postdoctoral Research: Cornell University 1969-1973
  • At Georgetown Since: 2002
  • Biographical Sketch
  • Contact: (202) 687-2092; rp55@georgetown.edu
     


Details:


Dengue viruses (types 1-4), members of Flaviviridae, are transmitted by mosquito vectors, Aedes aegypti and Aedes albopictus. They are recognized as the causative agents of diseases such as dengue fever, a simple self-limiting disease, to more severe forms, dengue hemorrhagic fever/dengue shock syndrome, affecting ~50-100 million people annually worldwide with thousands of fatalities. Over 40% of the world population is at risk for dengue viral infections and currently there is no effective vaccine or antiviral drug available. Moreover, infections caused by another member of the mosquito-borne Flaviviridae, West Nile virus, previously unknown in the U.S., have caused several thousand infections in birds and humans since 1999 epidemic in New York City. My laboratory has been involved (1) in understanding the role of cis-acting RNA elements and trans-acting factors involved in translation and replication of the viral genome, and (2) in identification of small molecule inhibitors of the viral protease, RNA helicase, and RNA-dependent RNA polymerase by a Structure-Activity Relationship (SAR) study.

Additional Research Information:

Dengue viruses have positive-strand RNA genomes with a 5'-cap structure. The viral RNA codes for a single polyprotein precursor; the precursor is processed by the host protease(s) as well as the two-component viral serine protease into at least 10 mature viral proteins. Processing by the viral protease requires the viral protein, NS2B, which acts as a cofactor to activate the N-terminal serine protease domain of NS3. The mechanism and the amino acid residues involved in activation are unknown and are currently under study. An in vitro protease assay was developed in our laboratory using E. coli-expressed and purified components of the viral protease. We have also developed a cell-based assay system using Dengue virus type 2 and 4 replicons and the respective replicon expressing mammalian cells to study the effects of protease inhibitors on viral replication. The C-terminal region of NS3 has an RNA-stimulated NTPase/RNA helicase and 5'-RNA triphosphatase activities which are excellent targets for antiviral therapy. In flavivirus-infected cells, NS3 and NS5, the RNA-dependent RNA polymerase (RdRP), exist as a complex. An in vitro replication system has been developed that utilizes cell-free system from dengue virus-infected mosquito and mammalian cells or purified recombinant NS5 and exogenous viral template RNAs. The identification of proteins and RNA structural motifs involved in viral replication using the in vitro and a cell-based assay system is pursued in our laboratory.



Publications:

  • Mark Manzano, Erin D. Reichert, Stephanie Polo, Barry Falgout, Wojciech Kasprzak, Bruce A. Shapiro, and Radhakrishnan Padmanabhan. Identification of Cis-acting elements in the 3’-untranslated region of the dengue virus type 2 RNA that modulate translation and replication J. Biol. Chem. published April 22, 2011 as doi:10.1074/jbc.M111.234302 (in press).
  • Wu R, Smidansky ED, Oh HS, Takhampunya R, Padmanabhan R, Cameron CE, Peterson BR. Synthesis of a 6-methyl-7-deaza analogue of adenosine that potently inhibits replication of polio and dengue viruses. J Med Chem. 2010 Nov 25;53(22):7958-66. Epub 2010 Oct 22.  
  • Alcaraz-Estrada SL, Manzano MI, Del Angel RM, Levis R, Padmanabhan R. Construction of Dengue virus type 4 reporter replicon and analysis of temperature sensitive mutations in nonstructural proteins 3 and 5. J. Gen. Virol. 2010 Jul 14. [Epub ahead of print]
  • Agis-Juárez RA, Galván I, Medina F, Daikoku T, Padmanabhan R, Ludert JE, del Angel RM. Polypyrimidine tract-binding protein is relocated to the cytoplasm and is required during dengue virus infection in Vero cells. J. Gen. Virol. 2009 Dec;90(Pt. 12):2893- 901. Epub 2009 Aug 19.
  • Ezgimen MD, Mueller NH, Teramoto T, Padmanabhan R.  Effects of detergents on the West Nile virus protease activity. Bioorg Med Chem. 2009 May 1;17(9):3278-82. Epub 2009 Apr 1.
  • Teramoto T, Kohno Y, Mattoo P, Markoff L, Falgout B, Padmanabhan R. Genome 3' end repair in dengue virus type 2. RNA. 2008 Dec;14(12):2645-56. Epub 2008 Oct 30.
  • Sampath A, Padmanabhan R. Molecular targets for flavivirus drug discovery. Antiviral Res. 2009 Jan;81(1):6-15. Epub 2008 Sep 15. Review.
  • Mueller NH, Pattabiraman N, Ansarah-Sobrinho C, Viswanathan P, Pierson TC, Padmanabhan R. Identification and biochemical characterization of small molecule inhibitors of West Nile Virus serine protease by a high throughput screen. Antimicrob Agents Chemother. 2008 Jul 7. [Epub ahead of print]
  • Yu L, Nomaguchi M, Padmanabhan R, Markoff L. Specific requirements for elements of the 5' and 3' terminal regions in flavivirus RNA synthesis and viral replication. Virology. 2008 Apr 25;374(1):170-85. Epub 2008 Jan 29.
  • Padmanabhan R, Mueller N, Reichert E, Yon C, Teramoto T, Kono Y, Takhampunya R, Ubol S, Pattabiraman N, Falgout B, Ganesh VK, Murthy K. Multiple enzyme activities of flavivirus proteins. Novartis Found Symp. 2006;277:74-84; discussion 84-6, 251-3. Review.


Medline publications list