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The Intrinsic Apoptotic Pathway01:31

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Internal cellular stress, such as cellular injury or hypoxia, triggers intrinsic apoptosis. The B-cell lymphoma 2 (Bcl-2) family of proteins are the primary regulators of the intrinsic apoptotic pathway. For example, during DNA damage, checkpoint proteins, such as Ataxia Telangiectasia Mutated (ATM protein) and Checkpoints Factor-2 (Chk2) proteins, are activated. These proteins phosphorylate p53 which further activates pro-apoptotic proteins, such as Bax, Bak, PUMA, and Noxa, and inhibits...
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A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...
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The extrinsic apoptotic pathway is initiated when extracellular death-inducing signals, such as specific cytokines, activate the death receptors expressed on the cell surface. The immune cells involved in this pathway are natural killer cells (NK cells) and cytotoxic T-lymphocytes. NK cells are critical in innate immune response, while cytotoxic T-lymphocytes are associated with adaptive immune response. These cells recognize specific receptors expressed on the altered cells and activate...
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Examining BCL-2 Family Function with Large Unilamellar Vesicles
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Bax assembles into large ring-like structures remodeling the mitochondrial outer membrane in apoptosis.

Lena Große1, Christian A Wurm2, Christian Brüser2

  • 1Department of Neurology, University Medical Center of Göttingen, Göttingen, Germany Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.

The EMBO Journal
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PubMed
Summary

Researchers found that Bax proteins form ring-like structures in the mitochondrial outer membrane, creating pores essential for apoptosis. These Bax assemblies are crucial for mitochondrial outer membrane permeabilization (MOMP) during programmed cell death.

Keywords:
Bcl‐2MICOScell deathmembrane curvaturesuperresolution microscopy

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Area of Science:

  • Cell biology
  • Molecular biology
  • Biophysics

Background:

  • Bcl-2 family proteins, Bax and Bak, are key regulators of apoptosis.
  • Bax translocation to mitochondria initiates outer membrane permeabilization (MOMP).
  • The precise mechanism of Bax-mediated MOMP remains unclear.

Purpose of the Study:

  • To elucidate the structural mechanisms of Bax-mediated mitochondrial outer membrane permeabilization (MOMP).
  • To visualize Bax assembly dynamics during apoptosis using super-resolution microscopy.

Main Methods:

  • STED (Stimulated Emission Depletion) nanoscopy to visualize protein structures.
  • Analysis of Bax and Bak protein assemblies in the mitochondrial outer membrane.
  • Investigation of protein distribution within Bax structures.

Main Results:

  • Activated Bax forms ring-like structures in the mitochondrial outer membrane, potentially with Bak.
  • These Bax rings surround openings devoid of mitochondrial outer membrane proteins (e.g., Tom20, Tom22, Sam50).
  • Bax assemblies are necessary but not sufficient for full cytochrome c release in Drp1 knockdown cells.

Conclusions:

  • Bax rings delineate pores crucial for Bax-mediated MOMP.
  • Super-resolution data provide direct evidence for large Bax-delineated pores in MOMP.
  • The formation of Bax assemblies is a critical step in initiating programmed cell death.