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Regulation of Bcl-xl channel activity by calcium
1Department of Pharmacology, Case Western Reserve University, Cleveland,Ohio 44106, USA.
Abstract:
Recent studies have demonstrated that the anti-apoptotic proteins, Bcl-2 and Bcl-xl, with the carboxyl-terminal hydrophobic domain removed, form cation-selective channels in the lipid bilayer reconstitution system. However, the regulatory properties of these channels are unknown. In this study, we investigated the ion-conducting properties of full-length Bcl-xl in the lipid bilayer reconstitution system. Our findings indicate that Bcl-xl forms a cation-selective channel that conducts sodium but not calcium and that Bcl-xl channel activity is reversibly inhibited by luminal calcium with a half-dissociation constant of approximately 60 microM. This calcium-dependent regulation of the Bcl-xl channel provides new insights into the roles of calcium and Bcl-2-related proteins in the programmed cell death pathway.
Insights
Full-length Bcl-xl protein forms a cation-selective channel, conducting sodium ions. Luminal calcium reversibly inhibits this channel, offering new insights into programmed cell death regulation.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Anti-apoptotic proteins Bcl-2 and Bcl-xl, when truncated, form cation-selective channels.
- The regulatory properties of these Bcl-xl channels remain largely unknown.
Purpose of the Study:
- To investigate the ion-conducting properties of full-length Bcl-xl.
- To explore the regulatory mechanisms of Bcl-xl channels in a lipid bilayer system.
Main Methods:
- Utilized a lipid bilayer reconstitution system.
- Examined ion selectivity (sodium vs. calcium) and channel activity.
- Assessed the effect of luminal calcium on channel function and determined inhibition constants.
Main Results:
- Full-length Bcl-xl forms a cation-selective channel permeable to sodium ions but not calcium ions.
- Channel activity is reversibly inhibited by luminal calcium.
- The half-dissociation constant for calcium inhibition was found to be approximately 60 microM.
Conclusions:
- Bcl-xl functions as a calcium-regulated cation channel.
- Calcium-dependent regulation of Bcl-xl channels offers new insights into programmed cell death.
- Bcl-2 family proteins may play a direct role in calcium signaling during apoptosis.