Structural destabilizing mutations transform Bcl-2 from an anti-apoptotic protein to a pro-apoptotic protein

Bcl-2 family proteins are highly conserved molecules that play an important role in controlling the release of apoptotic proteins from mitochondria. They have Bcl-2 homology (BH) domains that are characterized by both sequence and structural similarity and are essential for their interaction and function.

Antiapoptotic members of this family, including Bcl-2, Bcl-XL, and Mcl-1, are characterized by four BH domains (BH1–BH4). On the other hand, proapoptotic multi-BH members such as Bax, Bak, and Bok also have four BH domains.

In contrast, BH3-only members such as Bid and Bim possess only BH3 domains. Some His BH3-only proteins have the ability to directly activate Bax and Bak, leading to their homo-oligomerization and pore formation at the mitochondrial outer membrane (MOM). This process is important in the control of apoptosis.

Remarkably, the structures of multi-BH anti-apoptotic and pro-apoptotic proteins show remarkable similarities. The main question is the possibility of converting anti-apoptotic Bcl-2 into a pro-apoptotic protein similar to Bax by modifying key structural elements within Bcl-2.

To address this, a group of researchers from China and the United States elucidated the mechanism of apoptosis induced by structural instability mutations in the mitochondrial protein Bcl-2.

The researchers performed mutations at key amino acids within a highly conserved domain of the Bcl-2 protein. They discovered that glutamate at position 152 (E152) of the Bcl-2 protein plays a pivotal role in regulating its function. 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 the E152 mutation was introduced, a multimeric structure formed in the outer mitochondrial membrane. This structural change exposed more BH3 domains. and ultimately provided a pro-apoptotic function,” said Jialing Lin, correspondent for the study published in . mitochondrial communication.

Further mechanistic studies showed that mutation of E152 may abolish the formation of hydrogen bonds with K22 and S105, reducing the structural stability of Bcl-2, and that the K22 and S105 mutants also showed apoptosis similar to the mutants. It has been shown that it has a promoting function. E152. As a result, through in vitro liposome experiments, researchers found that both WT Bcl-2 and E152S mutant proteins are able to form large pores through tBid, which regulates the release of approximately 10 kd molecules within the membrane. .

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