Targeting the γ‐Herpesvirus Bcl‐2 – Mediated Inhibition of Autophagy and Apoptosis

γ‐herpesviruses (γHVs) are common human pathogens that encode homologs of the anti‐apoptotic cellular Bcl‐2 proteins, which are critical to viral reactivation and oncogenic transformation. Bcl‐X L , a cellular Bcl‐2 homolog, and the γHV68 Bcl‐2 homolog, M11, both bind to a BH3 domain within the key autophagy effector BECN1 with comparable affinities, resulting in the suppression of BECN1‐mediated autophagy. Despite this similarity, the different residues lining the binding site of M11 and Bcl‐X L dictate varying affinities for BH3 domains from diverse proteins. Here we delineate BECN1 differential specificity determinants for binding to M11 or Bcl‐X L by quantifying autophagy levels in cells expressing different BECN1 mutants and either M11 or Bcl‐X L , and we show that a G120E+D121A BECN1 mutant selectively prevents suppression of BECN1‐mediated autophagy by Bcl‐X L , but not by M11. We use isothermal titration calorimetry to identify a BECN1 BH3 domain‐derived peptide that selectively binds to M11, but not to Bcl‐X L . The X‐ray crystal structure of this peptide bound to M11 reveals the mechanism by which the M11 BH3 domain‐binding groove accommodates this M11‐specific peptide. Lastly, we have used this information to develop a cell‐permeable peptide inhibitor that selectively inhibits M11‐mediated, but not Bcl‐X L ‐mediated suppression of autophagy. We are now testing the ability of this inhibitor to selectively inhibit M11‐mediated suppression of apoptosis. This work was funded by NIH grants P20 RR015566 and P30 GM103332‐01, and NSF grant EPS‐0814442 to SS and CC; NIH grant R21 AI078108 and NSF grant HRD‐0811239 to SS.