TY - JOUR
T1 - Molecular basis of the regulation of Beclin 1-dependent autophagy by the γ-herpesvirus 68 Bcl-2 homolog M11
AU - Sinha, Sangita
AU - Colbert, Christopher L.
AU - Becker, Nils
AU - Wei, Yongjie
AU - Levine, Beth
N1 - Funding Information:
tance with synchrotron data collection. X-ray diffraction data used in this report are derived from work performed at Argonne National Laboratory, Structural Biology Center at the Advanced Photon Source. Argonne is operated by U. Chicago Argonne, LLC, for the U.S. Department of Energy, Office of Biological and Environmental Research under contract DE-AC02-06CH11357.
Funding Information:
Beclin 1 and Bif-1 have been shown to also form homo-oligomers.53,54 Binding of Beclin 1 to cBcl-2 has been shown to inhibit Beclin 1 interaction with PI3Kc3 or UVRAG, although neither protein appears to interact directly with the Beclin 1 BH3 domain.18,54 Further, it has been suggested that binding of various Bcl-2 homologs may prevent higher order oligomerization of Beclin 1.55Thus, it appears likely that binding of Bcl-2 homologs to Beclin 1 sterically hinders its interactions with other components of the autophagy nucleation complex, inhibiting the autophagy-inducing function of Beclin 1. The molecular mechanism of Beclin 1 in autophagy and consequently, the exact mechanism by which the Beclin 1-Bcl-2 interaction disrupts the autophagy function of Beclin 1, remains to be understood. Finally, this study not only furthers our knowledge of the regulation of Beclin 1, and consequently, the vital cellular process of autophagy, but also provides information regarding the subtle differences that constitute specificity determinants of the interac- tion of M11 with BH3 domains. Information regarding interaction specificity determinants will be useful for constructing mutant viruses to selectively examine the effects of M11 on either host cell autophagy or apoptosis, and consequently on viral pathogenesis and transformation of infected cells. For instance, the highest level of γHV Bcl-2 expression occurs immediately post-infection, abrogating host cell apoptosis, thus promoting virus survival. It is likely that inhibition of virus degradation by autophagy may be another key reason for the early expression γHV Bcl-2. Similarly, it has generally been believed that γHV Bcl-2s cause transformation of infected cells chiefly by inhibiting apoptosis. However, given the established role of Beclin 1 and autophagy in tumor suppression,31-35 it is quite possible, as has been discussed recently,16 that inhibition of autophagy may be another mechanism of malignant transformation of infected cells by viral Bcl-2 family members. Finally, information regarding interac- tion specificity determinants can also be used for the structure-based design of small molecules that selectively inhibit Beclin 1-γHV Bcl-2 Acknowledgements interactions and remove the γHV blockade of autophagy. Such inhib-This work was funded by NIH grants R21 AI078108 to S. S. and itors would provide a powerful tool to examine the role of autophagy R01 CA109168 to B.L. We thank Johann Deisenhofer for access in regulating γHV infection, and ultimately may even form the basis to facilities for protein purification and structure biology, Michael
PY - 2008/11/16
Y1 - 2008/11/16
N2 - γ-Herpesviruses (γHVs), including important human pathogens such as Epstein Barr virus, Kaposi's sarcoma-associated HV, and the murine γHV68, 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 γHV Bcl-2s. Here we investigate the γHV68 M11-Beclin 1 interaction in atomic detail, using biochemical and structural approaches. We show that the Beclin 1 BH3 domain is the primary determinant of binding to M11 and other Bcl-2s, and this domain binds in a hydrophobic groove on M11, reminiscent of the binding of different BH3 domains to other Bcl-2s. Unexpectedly, regions outside of, but contiguous with, the Beclin 1 BH3 domain also contribute to this interaction. We find that M11 binds to Beclin 1 more strongly than do KSHV Bcl-2 or cBcl-2. Further, the differential affinity of M11 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 1 residues L116 and F123, and M11 residue pairs G86 + R87 and Y60 + L74, are required for M11 to bind to Beclin 1 and downregulate autophagy. Thus, our results suggest that M11 inhibits autophagy through a mechanism that involves the binding of the Beclin 1 BH3 domain in the M11 hydrophobic surface groove.
AB - γ-Herpesviruses (γHVs), including important human pathogens such as Epstein Barr virus, Kaposi's sarcoma-associated HV, and the murine γHV68, 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 γHV Bcl-2s. Here we investigate the γHV68 M11-Beclin 1 interaction in atomic detail, using biochemical and structural approaches. We show that the Beclin 1 BH3 domain is the primary determinant of binding to M11 and other Bcl-2s, and this domain binds in a hydrophobic groove on M11, reminiscent of the binding of different BH3 domains to other Bcl-2s. Unexpectedly, regions outside of, but contiguous with, the Beclin 1 BH3 domain also contribute to this interaction. We find that M11 binds to Beclin 1 more strongly than do KSHV Bcl-2 or cBcl-2. Further, the differential affinity of M11 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 1 residues L116 and F123, and M11 residue pairs G86 + R87 and Y60 + L74, are required for M11 to bind to Beclin 1 and downregulate autophagy. Thus, our results suggest that M11 inhibits autophagy through a mechanism that involves the binding of the Beclin 1 BH3 domain in the M11 hydrophobic surface groove.
KW - Apoptosis
KW - Autophagy
KW - Bcl-2
KW - Beclin 1
KW - Viral Bcl-2
KW - γ-herpesvirus
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U2 - 10.4161/auto.6803
DO - 10.4161/auto.6803
M3 - Article
C2 - 18797192
AN - SCOPUS:58149095737
SN - 1554-8627
VL - 4
SP - 989
EP - 997
JO - Autophagy
JF - Autophagy
IS - 8
ER -