Fig. 1.
Viral proteins target specific elements of the mitochondrial checkpoint of apoptosis. According to a prevalent model, upon an apoptotic stimulus the BH3-only proteins (Bim, Noxa, Bid, Puma, Bmf, Bad) are induced or activated. They subsequently translocate to the mitochondria to inhibit the pro-survival Bcl-2 proteins (Bcl-2, Bcl-XL, Bcl-w, Mcl-1). Upon sequestration of pro-survival Bcl-2 proteins by BH3-only proteins, the pro-apoptotic Bcl-2 proteins Bak and Bax located in the outer mitochondrial membrane undergo structural rearrangements of their N-terminus, leading to their oligomerisation. The viral activators (pink) and inhibitors (purple) of apoptosis sequestering this pathway target specific subsets of Bcl-2 proteins, for details see text. Black lines indicate the cellular apoptotic pathway, red lines indicate viral inhibition, and red arrows indicate activation. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)