Related Experiment Videos
Rupture of the mitochondrial outer membrane impairs porin assembly
1Department of Pharmacology, Wayne State University, Detroit, Michigan 48201.
Abstract:
Outer membranes isolated from yeast mitochondria were capable mediating the in vitro insertion of porin. As with the outer membrane of intact mitochondria, the insertion was ATP-dependent, and the inserted porin was resistant to trypsin treatment after detergent solubilization. However, the extent of porin insertion into isolated outer membranes was much less per mg of outer membrane protein than with intact mitochondria. The greater efficiency of intact mitochondria was not due to contact site-mediated translocation as isolated contact sites were less able to insert porin than isolated outer membranes, and blockade of the contact site channel in intact mitochondria did not affect porin insertion. However, mitochondria that had been subjected to osmotic shock sufficient to rupture the outer membrane and deplete the contents of the intermembrane space (i.e. mitoplasts) lost most of their ability to insert porin. Since outer membranes are isolated from mitoplasts, the low insertion activity of mitoplasts explains the low efficiency of insertion into isolated outer membranes. These results also indicate that, unlike proteins that are imported to the inner membrane and matrix of the mitochondria, porin's assembly is severely reduced by breaching the outer membrane and depletion of the intermembrane space contents.
Insights
Yeast mitochondria outer membranes can insert porin (a mitochondrial protein) in vitro. This process is ATP-dependent, but less efficient than in intact mitochondria, requiring the intermembrane space contents for optimal porin insertion.
Area of Science:
- Mitochondrial biogenesis
- Protein import and assembly
- Cellular membrane biology
Background:
- Porin is a key protein forming channels in the mitochondrial outer membrane.
- Understanding porin insertion is crucial for mitochondrial function and integrity.
- Previous studies suggested ATP-dependent mechanisms for protein translocation across mitochondrial membranes.
Purpose of the Study:
- To investigate the in vitro insertion of porin into isolated yeast mitochondrial outer membranes.
- To compare the efficiency of porin insertion into isolated outer membranes versus intact mitochondria.
- To elucidate the role of the intermembrane space and contact sites in porin translocation.
Main Methods:
- Isolation of yeast mitochondrial outer membranes and intact mitochondria.
- In vitro assays for porin insertion into isolated membranes and intact organelles.
- Assessment of ATP-dependence and trypsin resistance of inserted porin.
- Investigation of contact site-mediated translocation and osmotic shock effects on mitoplasts.
Main Results:
- Isolated outer membranes mediated ATP-dependent porin insertion, similar to intact mitochondria.
- Porin insertion was significantly less efficient in isolated outer membranes compared to intact mitochondria.
- Mitochondria subjected to osmotic shock (mitoplasts) showed drastically reduced porin insertion ability.
- Contact sites did not appear to be essential for efficient porin insertion.
Conclusions:
- The intermembrane space contents are critical for efficient porin insertion into yeast mitochondria.
- Breaching the outer membrane and depleting the intermembrane space severely impairs porin assembly.
- Unlike matrix-targeted proteins, porin assembly is highly sensitive to the integrity of the mitochondrial outer membrane and intermembrane space.