The orf virus inhibitor of apoptosis functions in a Bcl-2-like manner, binding and neutralizing a set of BH3-only proteins and active Bax.
We have previously shown that the Orf virus protein, ORFV125, is a potent inhibitor of the mitochondrial pathway of apoptosis and displays rudimentary sequence similarities to cellular anti-apoptotic Bcl-2 proteins. Here we investigate the proposal that ORFV125 acts in a Bcl-2-like manner to inhibit apoptosis. We show that the viral protein interacted with a range of BH3-only proteins (Bik, Puma, DP5, Noxa and all 3 isoforms of Bim) and neutralized their pro-apoptotic activity. In addition, ORFV125 bound to the active, but not the inactive, form of Bax, and reduced the formation of Bax dimers. Mutation of specific amino acids in ORFV125 that are conserved and functionally important in mammalian Bcl-2 family proteins led to loss of both binding and inhibitory functions. We conclude that ORFV125's mechanism of action is Bcl-2-like and propose that the viral protein's combined ability to bind to a range of BH3-only proteins as well as the active form of Bax provides significant protection against apoptosis. Furthermore, we demonstrate that the binding profile of ORFV125 is distinct to that of other poxviral Bcl-2-like proteins.
Westphal
Dana
D
Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand.
Ledgerwood
Elizabeth C
EC
Tyndall
Joel D A
JD
Hibma
Merilyn H
MH
Ueda
Norihito
N
Fleming
Stephen B
SB
Mercer
Andrew A
AA
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D008969:Molecular Sequence Data; D009923:Orf virus / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D016415:Sequence Alignment; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*
D051017:Apoptosis Regulatory Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014764:Viral Proteins