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Signal peptidase can cleave inside a polytopic membrane protein.
J P Beltzer1, H P Wessels, M Spiess
1Department of Biochemistry, Biocenter, University of Basel; Switzerland
FEBS Letters
|August 14, 1989
Summary
Signal peptidase cleaves proteins entering the endoplasmic reticulum. This study shows signal peptidase can process internal sites within polytopic membrane proteins, challenging previous assumptions.
Area of Science:
- Molecular Biology
- Protein Processing
- Membrane Protein Biogenesis
Background:
- Signal peptides direct proteins to the endoplasmic reticulum for processing by signal peptidase.
- Polytopic proteins with multiple membrane-spanning segments often exhibit restricted signal peptidase cleavage, typically at the first hydrophobic domain.
Purpose of the Study:
- To investigate whether signal peptidase can cleave internal sequences within polytopic membrane proteins.
- To test the hypothesis that signal peptidase access is limited to the N-terminal signal sequence.
Main Methods:
- Constructed an artificial threefold membrane-spanning protein.
- Replaced the third transmembrane segment with a known signal sequence.
- Performed in vitro translation and microsome insertion assays.
Main Results:
- Efficient cleavage was observed at the introduced signal sequence within the polytopic protein.
- Demonstrated signal peptidase activity on an internal domain of a membrane protein.
Conclusions:
- Signal peptidase is capable of cleaving within polytopic membrane proteins at internal sites.
- The accessibility of cleavage sites, not just their sequence, influences signal peptidase processing in membrane proteins.