Publication Abstract from PubMed
Apoptosis is a tightly regulated process that plays a crucial role in the removal of virally infected cells; a process controlled by both pro- and anti-apoptotic members of the Bcl-2 family. The pro-apoptotic proteins Bak and Bax are regulated by anti-apoptotic Bcl-2 proteins and are also activated by a subset of proteins known as BH3-only proteins, which contain dual functions by directly activating Bak and Bax, or by sequestering and neutralizing anti-apoptotic members. Numerous viruses express proteins that prevent premature host cell apoptosis. Vaccinia virus encodes F1L, an anti-apoptotic protein essential for survival of infected cells that bears no discernible sequence homology to mammalian cell death inhibitors. Despite the limited sequence similarities, F1L has been shown to adopt a novel dimeric Bcl-2-like fold, which enables hetero-oligomeric binding to both Bak and the pro-apoptotic BH3-only protein Bim that ultimately prevents Bak and Bax homo-oligomerization. However, no structural data on the mode of engagement between F1L and its Bcl-2 counterparts is presently available. Here we solved the crystal structures of F1L in complex with two ligands, Bim and Bak. Our structures indicate that F1L can engage two BH3 ligands simultaneously via the canonical Bcl-2 ligand binding grooves. Furthermore, with the use of structure guided mutagenesis, we generated point mutants within the binding pocket of F1L in order to elucidate residues responsible for both Bim and Bak binding and prevention of apoptosis. We propose that the sequestration of Bim by F1L is primarily responsible for preventing apoptosis during vaccinia virus infection. IMPORTANCE: Numerous viruses have adapted strategies to counteract apoptosis by encoding proteins responsible for sequestering pro-apoptotic components. Vaccinia virus, the prototypical member of the orthopoxviridae encodes a protein known as F1L that functions to prevent apoptosis by interacting with Bak and the BH3-only protein Bim. Despite recent structural advances, little is known regarding the binding mechanics between F1L and the pro-apoptotic Bcl-2 members. Utilizing 3D-structures of F1L bound to host pro-apoptotic proteins we generated variants of F1L that neutralize Bim and/or Bak. We demonstrate that during vaccinia virus infection engagement of Bim and Bak by F1L is crucial for subverting host cell apoptosis.
Structural Insight Into BH3-Domain Binding of Vaccinia Virus Anti-Apoptotic F1L.,Campbell S, Thibault J, Mehta N, Colman PM, Barry M, Kvansakul M J Virol. 2014 May 21. pii: JVI.01092-14. PMID:24850748[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
