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Related Concept Videos

The Inner Mitochondrial Membrane01:28

The Inner Mitochondrial Membrane

The inner mitochondrial membrane is the primary site of ATP synthesis. The inner membrane domain that forms a smooth layer adjacent to the outer membrane is called the inner boundary membrane. This domain contains membrane transporters that drive metabolites in and out of the mitochondria.  In contrast, the inner membrane network that invaginates into the matrix space is called the cristae membrane. This domain accounts for principle mitochondrial function as it accommodates the protein...
Porin Insertion in the Outer Mitochondrial Membrane01:12

Porin Insertion in the Outer Mitochondrial Membrane

Porins are beta-barrel proteins translocated to the mitochondrial outer membrane through the TOM complex into the intermembrane space. Porin precursors bind TIM chaperones within the intermembrane space and are guided to the Sorting and Assembly Machinery complex or SAM complex on the outer mitochondrial membrane.
Three models describe the assembly of porins by the SAM complex and their insertion into the outer membrane. Model 1 suggests that porins are assembled outside the SAM channel as the...
Structure of Porins01:21

Structure of Porins

Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a  motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel precursors...
Negative Regulator Molecules01:23

Negative Regulator Molecules

Positive regulators allow a cell to advance through cell cycle checkpoints. Negative regulators have an equally important role as they terminate a cell’s progression through the cell cycle—or pause it—until the cell meets specific criteria.
Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...
Mitochondrial Membranes01:45

Mitochondrial Membranes

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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An Improved Method to Isolate Mitochondrial Contact Sites
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Prohibitin function within mitochondria: essential roles for cell proliferation and cristae morphogenesis.

Carsten Merkwirth1, Thomas Langer

  • 1Institute for Genetics, Centre for Molecular Medicine (CMMC), University of Cologne, 50674 Cologne, Germany.

Biochimica Et Biophysica Acta
|June 19, 2008
PubMed
Summary

Prohibitin proteins (PHB1 and PHB2) form mitochondrial inner membrane complexes that regulate cell proliferation and mitochondrial integrity. Their ring-like structure suggests a scaffolding role in organizing mitochondrial inner membrane functions.

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Area of Science:

  • Mitochondrial biology
  • Cellular membrane protein complexes
  • Protein structure and function

Background:

  • Prohibitins are conserved membrane proteins with proposed roles in various cellular compartments.
  • Large assemblies of prohibitin subunits PHB1 and PHB2 in the mitochondrial inner membrane are identified as the active structures.
  • These mitochondrial prohibitin complexes are known to influence cell proliferation, mitochondrial cristae morphogenesis, and overall mitochondrial integrity.

Purpose of the Study:

  • To elucidate the molecular mechanism underlying prohibitin function in mitochondria.
  • To investigate the role of prohibitin complexes in regulating mitochondrial dynamics, specifically OPA1 processing.
  • To explore the potential scaffolding function of prohibitins based on their assembly and sequence homology.

Main Methods:

  • Analysis of large prohibitin complexes (PHB1 and PHB2) in the mitochondrial inner membrane.
  • Investigation of prohibitin's effect on the processing of the dynamin-like GTPase OPA1.
  • Structural and sequence homology analysis comparing prohibitins to SPFH-family proteins.

Main Results:

  • Mitochondrial prohibitin complexes, composed of PHB1 and PHB2, are the physiologically active forms.
  • Prohibitin complexes critically affect OPA1 processing, a key event in mitochondrial fusion.
  • The ring-like assembly and sequence similarity to SPFH proteins suggest a scaffolding function for prohibitins.

Conclusions:

  • Prohibitins function as a ring-like assembly in the mitochondrial inner membrane, impacting cell proliferation and mitochondrial integrity.
  • The molecular mechanism involves scaffolding, potentially leading to functional compartmentalization within the inner mitochondrial membrane.
  • Understanding prohibitin scaffolding is crucial for comprehending mitochondrial dynamics and function.