IP3 receptor modulation by Bcl-2: from novel molecular determinants to disease-related mutations

Through prior research, the team of Dr. Bultynck discovered that the anti-apoptotic Bcl-2 proteins play an important cellular function at the endoplasmic reticulum (ER) as inhibitors of the intracellular calcium release channels, IP3 receptors (IP3R). Although a lot of progress was made in the study of IP3R/Bcl-2 complexes, many aspects on the molecular level are still unclear. The purpose of this project is three-fold: 1. Bcl-2 binds the ligand-binding region of the IP3R. However, the exact Bcl-2 binding site in this region is unknown. Elucidation of the exact binding site would allow the team to compare the role of Bcl-2 binding to the central modulating region of the IP3R with Bcl-2 binding to the ligand binding domain. 2. Bcl-2 binds the IP3R with its BH4 domain. However, when looking at its 3D structure, the IP3R regions that interact with Bcl-2's BH4 domain are located relatively far from the ER membrane, which is where Bcl-2 resides. Thusly, we postulate that the Bcl-2 BH4 domain has the ability to 'detach' from the rest of the Bcl-2 structure via an unstructured loop located between the BH4 domain and the rest of the Bcl-2 protein. This hypothesis will be explored using Bcl-2 proteins from which the unstructured loop was removed. 3. Bcl-2 is upregulated in cancer but it is also mutated in DLBCL and in CLL with acquired resistance against BH3 mimetica (venetoclax). The influence of these cancer related Bcl-2 mutations on the regulation of the IP3R will be explored.