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Bacteriophage M13 procoat protein inserts into the plasma membrane as a loop structure
1Microbiology Department, University of Basel, Switzerland.
Abstract:
The major coat protein of bacteriophage M13 is synthesized as a precursor, the procoat, with a typical leader (signal) sequence of 23 residues at its NH2-terminus. A fusion protein that contains the NH2-terminal 141 residues of cytoplasmic ribulokinase and all but the first ten residues of M13 procoat was made. The fusion protein inserts into the plasma membrane of Escherichia coli and is processed by leader peptidase to give rise to a leader peptide of 155 residues and the mature coat protein of 50 residues. The NH2-terminus of the leader peptide remains in the cytoplasm and is protected from protease added to the medium outside of the cell. This indicates that M13 procoat inserts into the membrane as a loop structure and that the NH2-terminus of a leader peptide remains within the cytoplasm during membrane insertion.
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Bacteriophage M13 procoat inserts into the bacterial membrane as a loop. The leader peptide
Area of Science:
- Molecular Biology
- Bacteriophage Biology
- Membrane Protein Insertion
Background:
- The major coat protein of bacteriophage M13 is synthesized as a precursor, procoat.
- Procoat contains a 23-residue N-terminal leader sequence essential for membrane insertion.
Purpose of the Study:
- To investigate the membrane insertion mechanism of bacteriophage M13 procoat.
- To determine the topology of the leader peptide during membrane insertion.
Main Methods:
- Construction of a fusion protein: M13 procoat fused to cytoplasmic ribulokinase.
- Expression of the fusion protein in Escherichia coli.
- Analysis of protein processing and topology using leader peptidase and protease protection assays.
Main Results:
- The fusion protein inserts into the Escherichia coli plasma membrane.
- Leader peptidase processes the fusion protein into a leader peptide and mature coat protein.
- The N-terminus of the leader peptide remains in the cytoplasm, protected from external protease.
Conclusions:
- Bacteriophage M13 procoat inserts into the membrane via a loop structure.
- The N-terminus of the M13 procoat leader peptide remains in the cytoplasm during membrane insertion.