A Step Forward toward Selective Activation/Inhibition of Bak, a Pro-Apoptotic Member of the Bcl-2 Protein Family: Discovery of New Prospective Allosteric Sites Using Molecular Dynamics.

Bak is a pro-apoptotic protein and a member of the Bcl-2 family that plays a key role in apoptosis, a programmed cell death mechanism of multicellular organisms. Its activation under death stimuli triggers the permeabilization of the mitochondrial outer membrane that represents a point of no return in the apoptotic pathway. This process is deregulated in many tumors where Bak is inactivated, whereas in other cases like in neurodegeneration, it exhibits an excessive response leading to disorders such as the Alzheimer disease. Members of the Bcl-2 family share a common 3D structure, exhibiting an extremely similar orthosteric binding site, a place where both pro and antiapoptotic proteins bind. This similarity raises a selectivity issue that hampers the identification of new drugs, capable of altering Bak activation in a selective manner. An alternative activation site triggered by antibodies has been recently identified, opening the opportunity to undertake new drug discovery studies. Despite this recent identification, an exhaustive study to identify cryptic pockets as prospective allosteric sites has not been yet performed. Thus, the present study aims to characterize novel hotspots in the Bak structure. For this purpose, we have carried out extensive molecular dynamics simulations using three different Bak systems including Bak in its apo form, Bak in complex with its endogen activator Bim and an intermediate form, set up by removing Bim from the previous complex. The results reported in the present work shed some light on future docking studies on Bak through the identification of new prospective allosteric sites, not previously described in this protein.