Molecular basis of the regulation of Beclin 1-dependent autophagy by the γ-herpesvirus 68 Bcl-2 homolog M11

gamma-Herpesviruses (gamma HVs), including important human pathogens such as Epstein Barr virus, Kaposi's sarcoma-associated W, and the murine gamma HV68, encode homologs of the antiapoptotic, cellular Bcl-2 (cBcl-2) to promote viral replication and pathogenesis. The precise molecular details by which these proteins function in viral infection are poorly understood. Autophagy, a lysosomal degradation pathway, is inhibited by the interaction of cBcl-2s with a-key autophagy effector, Beclin 1, and can also be inhibited by gamma HV Bcl-2s. Here we investigate the gamma HV68 M11-Beclin 1 interaction in atomic detail, using biochemical and structural approaches. We show that the Beclin I BH3 domain is the primary determinant of binding to M11 and other Bcl-2s, and this domain binds in a hydrophobic groove on M 11, reminiscent of the binding of different BH3 domains to other Bcl-2s. Unexpectedly, regions outside of, but contiguous with, the Beclin I BH3 domain also contribute to this interaction. We find that M 11 binds to Beclin I more strongly than do KSHV Bcl-2 or cBcl-2. Further, the differential affinity of M 11 for different BH3 domains is caused by subtle, yet significant, variations in the atomic details of each interaction. Consistent with our structural analysis, we find that Beclin I residues L116 and F 123, and M 11 residue pairs G86 + R87 and Y60 + L74, are required for M 11 to bind to Beclin I and downregulate autophagy. Thus, our results suggest that M 11 inhibits autophagy through a mechanism that involves the binding of the Beclin I BH3 domain in the M 11 hydrophobic surface groove.