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Amino acid replacement in a mutant lipoprotein of the Escherichia coli outer membrane
Abstract:
The primary structure of a mutant lipoprotein of the outer membrane of Escherichia coli was investigated. This mutant was previously described as a mutant that forms a dimer of the lipoprotein by an S-S bridge (H. Suzuki et al., J. Bacteriol. 127:1494-1501, 1976). The amino acid analysis of the mutant lipoprotein revealed that the mutant lipoprotein had an extra cysteine residue, with concomitant loss of an arginine residue. From the analysis of the mutant lipoprotein revealed that the mutant lipoprotein had an extra cysteine residue, with concomitant loss of an arginine residue. From the analysis of tryptic peptides, it was found that the arginine residue at position 57 was replaced with a cysteine residue. The amino terminal structure of the mutant lipoprotein was found to be glycerylcysteine, as in the case of the wild-type lipoprotein. The present results show that the mutation that was previously determined to map at 36.5 min on the E. coli chromosome occurred in the structure gene (lpp) for the lipoprotein. This was further confirmed by the fact that a merodiploid carrying both lpp+ and lpp produces not only the wild-type lipoprotein but also the mutant lipoprotein.
Insights
Researchers investigated a mutant Escherichia coli lipoprotein, identifying an extra cysteine and lost arginine residue. This mutation in the lipoprotein structure gene (lpp) explains the observed S-S bridge dimer formation.
Area of Science:
- Microbiology
- Molecular Biology
- Protein Chemistry
Background:
- Investigating the primary structure of outer membrane proteins is crucial for understanding bacterial cell envelope function.
- Previous studies identified a mutant Escherichia coli lipoprotein forming dimers via disulfide bridges.
Purpose of the Study:
- To elucidate the primary structure of a mutant Escherichia coli lipoprotein.
- To confirm the genetic basis of the observed lipoprotein mutation.
Main Methods:
- Amino acid analysis of the mutant lipoprotein.
- Tryptic peptide analysis to identify specific residue changes.
- Genetic complementation using merodiploids.
Main Results:
- The mutant lipoprotein contains an additional cysteine residue with a corresponding loss of an arginine residue.
- Analysis revealed arginine at position 57 is replaced by cysteine.
- The mutation was confirmed to be in the lipoprotein structure gene (lpp).
Conclusions:
- The mutation responsible for the S-S bridge dimer formation in E. coli lipoprotein is located within the lpp gene.
- The specific mutation involves an arginine to cysteine substitution at position 57.