Structure-Destabilizing Mutations Transform Bcl-2 from an Antiapoptotic Protein into a Proapoptotic Protein

Bcl-2 family proteins are highly conserved molecules that play a crucial role in regulating the release of apoptotic proteins from mitochondria. They possess Bcl-2 homology (BH) domains, which are characterized by both sequence and structural similarities, and are essential for their interactions and functions.

The antiapoptotic members of this family, including Bcl-2, Bcl-XL, and Mcl-1, feature four BH domains (BH1 to BH4). On the other hand, proapoptotic multi-BH members like Bax, Bak, and Bok also have four BH domains. In contrast, BH3-only members such as Bid and Bim only possess the BH3 domain. Some BH3-only proteins have the ability to directly activate Bax and Bak, leading to their homo-oligomerization and the formation of pores in the mitochondrial outer membrane (MOM). This process is critical in regulating apoptosis.

Surprisingly, the structures of multi-BH anti and proapoptotic proteins exhibit remarkable similarities. The main question lies in the possibility of transforming anti-apoptotic Bcl-2 into pro-apoptotic proteins resembling Bax by modifying key structural elements within Bcl-2.

The researchers conducted mutations on critical amino acids within a highly conserved domain of the Bcl-2 protein. They found that glutamate at position 152 (E152) in the Bcl-2 protein plays a pivotal role in regulating its functionality. Mutations at E152 (E152A, E152C, E152S) were able to induce apoptosis by liberating cytochrome c from mitochondria in cells lacking Bax and Bak.

“Interestingly, when the transmembrane region of the Bcl-2 protein was excised, and E152 mutations were introduced, a multimeric structure formed in the mitochondrial outer membrane. This structural change exposed more BH3 domains, ultimately resulting in a pro-apoptotic function,” shared Jialing Lin, corresponding to the study published in the KeAi journal Mitochondrial Communications.

Further mechanism studies showed that the mutation of E152 could eliminate the formation of hydrogen bonds with K22 and S105, thus reducing the structural stability of Bcl-2, and the mutants of K22 and S105 also had pro-apoptotic functions similar to that of the mutant E152. Consequently, through in vitro liposome experiments, the researchers found that both WT Bcl-2 and E152S mutant proteins can form large pores mediated by tBid, which regulated the release of molecules about 10kd in the membrane.

“Our study contributes to the existing literature on apoptosis,” says co-corresponding author Quan Chen. “It introduces fresh concepts and potential avenues for the development of adjuvant drugs targeting Bcl-2 as a cancer treatment approach.”

Contact author name, affiliation, email address:
Quan Chen, The State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, P. R. China, Tel: 86-10-6480-7321, Fax: 86-10-6480-7321, Email: chenq@ioz.ac.cn

Jialing Lin, Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73126, USA, Tel: 01-405-271-2227 ext. 61216, Fax: 01-405-271-3092, Email: jialing-lin@ouhsc.edu

Funder: This work was supported by National Natural Science Foundation of China Grant (32230046) to Q. C., National Natural Science Foundation of China Grants (92254301) to L. L., US National Institutes of Health Grant (R01GM062964) and Presbyterian Health Foundation Bridge Grant (20221568) to J. L., and by an Institutional Development Award from the National Institute of General Medical Sciences of US National Institutes of Health (P20GM103640).

Conflict of interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

See the article: Ping Gao, et al., Structure-destabilizing mutations unleash an intrinsic perforation activity of antiapoptotic Bcl-2 in the mitochondrial membrane enabling apoptotic cell death, Mitochondrial Communications, Volume 1, 2023, Pages 48-61.  https://doi.org/10.1016/j.mitoco.2023.08.001