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The endoplasmic reticulum membrane is permeable to small molecules.
Sylvie Le Gall1, Andrea Neuhof, Tom Rapoport
1Department of Cell Biology, Howard Hughes Medical Institute/Harvard Medical School, Boston, Massachusetts 02115-6091, USA.
Molecular Biology of the Cell
|November 18, 2003
Summary
The endoplasmic reticulum (ER) membrane is surprisingly permeable to small molecules, unlike other cell membranes. This increased leakiness may be essential for protein folding and ER functions.
Area of Science:
- Cell Biology
- Membrane Biology
- Biochemistry
Background:
- The endoplasmic reticulum (ER) lumen has a distinct composition compared to the cytosol.
- The permeability of the ER membrane to various molecules is not well understood.
- Cellular membranes typically exhibit low permeability to maintain compartmentalization.
Purpose of the Study:
- To investigate the permeability of the ER membrane to small, nonphysiological molecules.
- To compare the ER membrane's permeability with that of other cellular membranes.
- To understand the functional implications of ER membrane permeability.
Main Methods:
- Testing the passage of chemical modification reagents across isolated ER vesicles.
- Assessing ER membrane permeability in permeabilized cells using charged and polar reagents.
- Evaluating passive diffusion by conducting experiments at low temperatures.
Main Results:
- Isolated ER vesicles readily permit the entry of chemical modification reagents into the lumen.
- The ER membrane allows passage of a small, charged molecule impermeable to plasma and other organelle membranes.
- A larger polar molecule (~5 kDa) cannot permeate the ER membrane.
- Small molecule permeation is a passive process, independent of cellular energy.
Conclusions:
- The ER membrane is significantly more permeable than other cellular membranes.
- This enhanced permeability is a passive process.
- ER membrane leakiness may play a crucial role in protein folding and other ER functions.