Structural basis of apoptosis inhibition by the fowlpox virus protein FPV039

J Biol Chem. 2017 Jun 2;292(22):9010-9021. doi: 10.1074/jbc.M116.768879. Epub 2017 Apr 14.


Programmed cell death or apoptosis of infected host cells is an important defense mechanism in response to viral infections. This process is regulated by proapoptotic and prosurvival members of the B-cell lymphoma 2 (Bcl-2) protein family. To counter premature death of a virus-infected cell, poxviruses use a range of different molecular strategies including the mimicry of prosurvival Bcl-2 proteins. One such viral prosurvival protein is the fowlpox virus protein FPV039, which is a potent apoptosis inhibitor, but the precise molecular mechanism by which FPV039 inhibits apoptosis is unknown. To understand how fowlpox virus inhibits apoptosis, we examined FPV039 using isothermal titration calorimetry, small-angle X-ray scattering, and X-ray crystallography. Here, we report that the fowlpox virus prosurvival protein FPV039 promiscuously binds to cellular proapoptotic Bcl-2 and engages all major proapoptotic Bcl-2 proteins. Unlike other identified viral Bcl-2 proteins to date, FPV039 engaged with cellular proapoptotic Bcl-2 with affinities comparable with those of Bcl-2's endogenous cellular counterparts. Structural studies revealed that FPV039 adopts the conserved Bcl-2 fold observed in cellular prosurvival Bcl-2 proteins and closely mimics the structure of the prosurvival Bcl-2 family protein Mcl-1. Our findings suggest that FPV039 is a pan-Bcl-2 protein inhibitor that can engage all host BH3-only proteins, as well as Bcl-2-associated X, apoptosis regulator (Bax) and Bcl-2 antagonist/killer (Bak) proteins to inhibit premature apoptosis of an infected host cell. This work therefore provides a mechanistic platform to better understand FPV039-mediated apoptosis inhibition.

Keywords: B-cell lymphoma 2 (Bcl-2) family; X-ray crystallography; apoptosis; isothermal titration calorimetry (ITC); poxvirus; small-angle X-ray scattering (SAXS).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis Regulatory Proteins / chemistry*
  • Apoptosis Regulatory Proteins / genetics
  • Apoptosis Regulatory Proteins / metabolism
  • Avian Proteins / chemistry
  • Avian Proteins / genetics
  • Avian Proteins / metabolism
  • Chickens
  • Crystallography, X-Ray
  • Fowlpox virus / chemistry*
  • Fowlpox virus / genetics
  • Fowlpox virus / metabolism
  • Humans
  • Myeloid Cell Leukemia Sequence 1 Protein / chemistry
  • Myeloid Cell Leukemia Sequence 1 Protein / genetics
  • Myeloid Cell Leukemia Sequence 1 Protein / metabolism
  • Protein Domains
  • Viral Proteins / chemistry*
  • Viral Proteins / genetics
  • Viral Proteins / metabolism
  • bcl-2-Associated X Protein / chemistry
  • bcl-2-Associated X Protein / genetics
  • bcl-2-Associated X Protein / metabolism


  • Apoptosis Regulatory Proteins
  • Avian Proteins
  • BAX protein, human
  • MCL1 protein, human
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Viral Proteins
  • bcl-2-Associated X Protein

Associated data

  • PDB/2VOG
  • PDB/3PK1
  • PDB/4HW4
  • PDB/5TZQ
  • PDB/5TZP