The role of the N-terminus of Vaccinia virus F1L in apoptosis regulation — ASN Events
  1. Schedule
  2. Session 12: Poster Session D - Including Happy Hour & Trade Display
  3. The role of the N-terminus of Vaccinia virus F1L in apoptosis regulation

The role of the N-terminus of Vaccinia virus F1L in apoptosis regulation (#412)

Sofia Caria 1 , Bevan Marshall 1 , Christine Hawkins 1 , Michelle Barry 2 , Marc Kvansakul 1
  1. La Trobe University, Bundoora, VIC, Australia
  2. Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada, University of Alberta, Edmonton, Alberta, Canada

Anti-apoptotic Bcl-2 proteins are efficient inhibitors of cell death.  Viruses, including poxvirus, have evolved viral pro-survival Bcl-2 proteins (vBcl-2) to ensure their own survival1. These proteins inhibit the multimerisation of Bax and Bak, thus preventing outer mitochondrial membrane permeabilization and subsequent host cell apoptosis via the intrinsic apoptotic pathway2,3,4.

Vaccinia virus (VACV) belongs to the poxvirus family, being well known for its role as a vaccine in smallpox eradication. VACV encodes F1L, a protein which shares structural and functional homology to mammalian pro-survival Bcl-2 proteins5. 

Recent studies have suggested that F1L acts as a caspase-9 inhibitor through its N-terminus region. It was shown that an N-terminal 15-residue conserved sequence is responsible for this interaction and modeling studies suggest that two alpha helical sections in that region enable this interaction6,7.  

Our structural and biochemical studies indicate that F1L does not function as a caspase-9 inhibitor. A small-angle X-ray scattering (SAXS) model of F1L with an intact N-terminus was obtained through rigid-body modeling with Bunch5,8. 

This model is compatible with scattering by a protein harbouring a flexible/unstructred region. Taking into account our previously determined crystal structure5 the scattering data suggests that the F1L N-terminus is unstructured. Additional functional assays using yeast have shown that VACV F1L blocks yeast growth arrest in the presence of Bak but not in the presence of Bax or Apaf/caspase 9/caspase3, indicating that F1L regulates apoptosis via inhibtion of Bak. Removal of the F1L N-terminus did not affect the ability of F1L to ablate cell death, suggesting that this region is of no relevance for apoptosis inhibition by F1L.

  1. Galluzzi, L., et al., Viral control of mitochondrial apoptosis. PLoS Pathog, 2008. 4(5): p. e1000018.
  2. Antonsson, B., et al., Bax is present as a high molecular weight oligomer/complex in the mitochondrial membrane of apoptotic cells. J Biol Chem, 2001. 276(15): p. 11615-23.
  3. Griffiths, G.J., et al., Cell damage-induced conformational changes of the pro-apoptotic protein Bak in vivo precede the onset of apoptosis. J Cell Biol, 1999. 144(5): p. 903-14.
  4. Mikhailov, V., et al., Association of Bax and Bak homo-oligomers in mitochondria. Bax requirement for Bak reorganization and cytochrome c release. J Biol Chem, 2003. 278(7): p. 5367-76.
  5. Kvansakul, M., et al., Vaccinia virus anti-apoptotic F1L is a novel Bcl-2-like domain-swapped dimer that binds a highly selective subset of BH3-containing death ligands. Cell Death Differ, 2008. 15(10): p. 1564-71.
  6. Yu, E., et al., Structural determinants of caspase-9 inhibition by the vaccinia virus protein, F1L. J Biol Chem, 2011. 286(35): p. 30748-58.
  7. Zhai, D., et al., Vaccinia virus protein F1L is a caspase-9 inhibitor. J Biol Chem, 2010. 285(8): p. 5569-80.
  8. Petoukhov, M.V. and D.I. Svergun, Global rigid body modeling of macromolecular complexes against small-angle scattering data. Biophys J, 2005. 89(2): p. 1237-50.