Structural insight into African swine fever virus A179L mediated inhibition of apoptosis

Programmed cell death is a tightly controlled process critical for the removal of damaged or infected cells. Pro- and anti-apoptotic proteins of the Bcl-2 family are pivotal mediators of this process. African Swine Fever virus (ASFV) is a large DNA virus, the only member of the Asfarviridae family, and harbors A179L, a putative Bcl-2 like protein. A179L has been shown to bind to several pro-apoptotic Bcl-2 proteins, however the hierarchy of binding and the structural basis for apoptosis inhibition are currently not understood. We systematically evaluated the ability of A179L to bind pro-apoptotic Bcl-2 family members, and show that A179L is the first anti-apoptotic Bcl-2 protein to bind to all major death inducing mammalian Bcl-2 proteins. We then defined the structural basis for apoptosis inhibition of A179L by determining crystal structures of A179L bound to both Bid and Bax BH3 motifs. Our findings provide a mechanistic understanding for the potent anti-apoptotic activity of A179L by identifying it as the first pan pro-death Bcl-2 binder, and serve as a platform for more detailed investigations into the role of A179L during ASFV infection.IMPORTANCE Numerous viruses have acquired strategies to subvert apoptosis by encoding proteins capable of sequestering pro-apoptotic host proteins. African Swine Fever virus (ASFV), a large DNA virus and the only member of the Asfarviridae family, encodes the protein A179L that functions to prevent apoptosis. We show that A179L is unusual amongst anti-apoptotic Bcl-2 proteins in being able to physically bind to all core death inducing mammalian Bcl-2 proteins. Currently, little is known regarding the molecular interactions between A179L and the pro-apoptotic Bcl-2 members. Using crystal structures of A179L bound to two of the identified pro-apoptotic Bcl-2 proteins, Bid and Bax, we now provide a 3D view of how A179L sequesters host pro-apoptotic proteins, which is crucial for subverting premature host cell apoptosis.