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Updated: May 17, 2026
Examining BCL-2 Family Function with Large Unilamellar Vesicles
Published on: October 5, 2012
Profiling of the Bcl-2/Bcl-X(L)-binding sites on type 1 IP(3) receptor
Giovanni Monaco1, Marjolein Beckers, Hristina Ivanova
1Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, KU Leuven Campus Gasthuisberg O/N-I bus 802, Herestraat 49, BE-3000 Leuven, Belgium.
Abstract:
Several members of the anti-apoptotic Bcl-2-protein family, including Bcl-2, Bcl-X(L) and Mcl-1, directly bind and regulate the inositol 1,4,5-trisphosphate receptor (IP(3)R), one of the two main intracellular Ca(2+)-release channel types present in the endoplasmic reticulum. However, the molecular determinants underlying their binding to the IP(3)R remained a matter of debate. One interaction site for Bcl-2 was proposed in the central part of the modulatory domain [Y.P. Rong, A.S. Aromolaran, G. Bultynck, F. Zhong, X. Li, K. McColl, S. Matsuyama, S. Herlitze, H.L. Roderick, M.D. Bootman, G.A. Mignery, J.B. Parys, H. De Smedt, C.W. Distelhorst, Targeting Bcl-2-IP3 receptor interaction to reverse Bcl-2's inhibition of apoptotic calcium signals, Mol. Cell 31 (2008) 255-265] and another site in the C-terminal domain of the IP(3)R encompassing the sixth transmembrane domain, to which Bcl-2, Bcl-X(L) and Mcl-1 can bind [E.F. Eckenrode, J. Yang, G.V. Velmurugan, J.K. Foskett, C. White, Apoptosis protection by Mcl-1 and Bcl-2 modulation of inositol 1,4,5-trisphosphate receptor-dependent Ca(2+) signaling, J. Biol. Chem. 285 (2010) 13678-13684]. Here, we investigated and compared the binding of Bcl-2 and Bcl-X(L) to both sites. Two different IP(3)R domains were used for the C-terminal site: one lacking and one containing the sixth transmembrane domain. Our results show that elements preceding the C-terminal cytosolic tail located at the sixth transmembrane domain of IP(3)R1 were critical for recruiting both Bcl-2 and Bcl-X(L) to the C-terminal part of the IP(3)R. Furthermore, consistent with our previous observations, Bcl-X(L) bound with higher efficiency to the C-terminal part of the IP(3)R and to a much lesser extent to the central, modulatory domain, while Bcl-2 targeted both sites with similar efficiencies. In conclusion, IP(3)R harbors two different binding sites for anti-apoptotic Bcl-2 proteins, one in the central, modulatory domain and one in the C-terminal domain near the Ca(2+)-channel pore.
Insights
Anti-apoptotic Bcl-2 proteins bind the inositol 1,4,5-trisphosphate receptor (IP(3)R) at two distinct sites. Elements near the IP(3)R
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- Anti-apoptotic Bcl-2 proteins regulate intracellular calcium (Ca2+) signaling by binding to the inositol 1,4,5-trisphosphate receptor (IP(3)R).
- The precise molecular interactions and binding sites between Bcl-2 family proteins and IP(3)R have been debated.
- Previous studies proposed two potential binding sites: one in the central modulatory domain and another in the C-terminal domain near the Ca2+-release channel.
Purpose of the Study:
- To investigate and compare the binding characteristics of Bcl-2 and Bcl-X(L) to the proposed IP(3)R binding sites.
- To identify the specific regions within the IP(3)R C-terminal domain critical for Bcl-2 protein recruitment.
- To elucidate the differential binding affinities of Bcl-2 and Bcl-X(L) to distinct IP(3)R domains.
Main Methods:
- Utilized two distinct IP(3)R domains for C-terminal binding assays: one lacking and one including the sixth transmembrane domain.
- Performed comparative binding experiments to assess the interaction of Bcl-2 and Bcl-X(L) with both the central and C-terminal IP(3)R sites.
- Analyzed the role of the sixth transmembrane domain and preceding elements in recruiting Bcl-2 proteins to the IP(3)R.
Main Results:
- Elements preceding the C-terminal cytosolic tail at the sixth transmembrane domain of IP(3)R1 are crucial for recruiting both Bcl-2 and Bcl-X(L).
- Bcl-X(L) demonstrated higher binding efficiency to the C-terminal IP(3)R region compared to the central modulatory domain.
- Bcl-2 exhibited similar binding efficiencies to both the central and C-terminal IP(3)R sites, indicating broader interaction capabilities.
Conclusions:
- The inositol 1,4,5-trisphosphate receptor (IP(3)R) possesses two distinct binding sites for anti-apoptotic Bcl-2 proteins.
- One site is located in the central modulatory domain, and the other is in the C-terminal domain, adjacent to the Ca2+-channel pore.
- The sixth transmembrane domain and associated elements play a critical role in mediating the interaction of Bcl-2 proteins with the IP(3)R.
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