Amino-acid composition of the covalent rigid-layer lipoprotein in cell walls of Proteus mirabilis

Characterization of a new murein-associated lipoprotein in the outer membrane of Proteus mirabilis

A murein-associated outer membrane protein from Proteus mirabilis has been isolated. Since the protein carries ester- as well as amide-linked fatty acids it can be classified as a second outer membrane lipoprotein. An apparent molecular weight of 15,000 for this protein was determined from amino acid analysis and sodium dodecylsulfate/polyacrylamide gel electrophoresis. The amino acid composition, however, does not show similarities with the amino acid composition of the lipoprotein covalently linked to murein, which has a molecular weight of 7,300 as described previously in Proteus mirabilis.

Characterization of the cell wall and cell wall proteins of Chromatium vinosum

Highly purified cell walls of Chromatium vinosum were isolated by differential centrifugation, with or without Triton X-100 extraction. The isolated material had a protein composition similar to that of cell walls obtained by sucrose density gradient centrifugation. Twenty-two proteins were reproducibly detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A 42-kilodalton protein was shown to account for 65% of the total cell wall protein. The majority of cell wall proteins were solubilized in sodium dodecyl sulfate at room temperature; however, they existed as high-molecular-weight complexes unless heated to 45 degrees C or above. The cell wall contained one heat-modifiable protein which migrated with an apparent molecular weight of 37,400 when solubilized at 70 degrees C or below, but which migrated with an apparent molecular weight of 52,500 if solubilized at 100 degrees C. The electrophoretic mobility of three proteins was modified by 2-mercaptoethanol. The majority of C. vinosum cell wall proteins had isoelectric points between pH 4.5 and 5.5, and the 42-kilodalton protein focused at pH 4.9. No proteins were detected which were analogous to the lipoprotein or peptidoglycan-associated proteins of the Enterobacteriaceae. Nearest-neighbor analysis with a reducible, cross-linking reagent indicated that three proteins, including the 42-kilodalton protein, associated with themselves. Most of the cell wall proteins were partially accessible to proteases in both intact cells and isolated cell walls. Protease treatment of the whole cell or isolated cell wall digested approximately an 11,000-molecular-weight portion of the 42-kilodalton protein.

Covalent linkage of lipoprotein to peptidoglycan is not essential for outer membrane stability in Proteus mirabilis

Isolated rigis layers from Proteus mirabilis harvested at different growth phases were degraded by endo-N-acetylmuramidase from Chalaropsis B, and the degradation products were investigated. The results show the complete absence of covalently linked lipoprotein in exponential-phase cultures. Stationary cells, however, possess covalently linked lipoprotein in amounts similar to those found in Escherichia coli or Salmonella typhimurium during all growth phases. The overall peptidoglycan structure did not change during transition from logarithmic to stationary growth. Implications of these findings for the organization of the outer membrane are discussed.

Homology of the gene coding for outer membrane lipoprotein within various Gram-negative bacteria

The mRNA for a major outer membrane lipoprotein from Escherichia coli was found to hybridize specifically with one of the EcoRI and one of the HindIII restriction endonuclease-generated fragments of total DNA from nine bacteria in the family Enterobacteriaceae: E. coli, Shigella dysenteriae, Salmonella typhimurium, Citrobacter freundii, Klebsiella aerogenes, Enterobacter aerogenes, Edwardsiella tarda, Serratia marcescens, and Erwinia amylovora. However, among the Enterobacteriaceae, DNA from two species of Proteus (P. mirabilis and P. morganii) did not contain any restriction endonuclease fragments that hybridized with the E. coli lipoprotein mRNA. Furthermore, no hybrid bands were detected in four other gram-negative bacteria outside the family Enterobacteriaceae: Pseudomonas aeruginosa, Acinetobacter sp. HO1-N, Caulobacter crescentus, and Myxococcus xanthus. Envelope fractions from all bacteria in the family Enterobacteriaceae tested above cross-reacted with antiserum against the purified E. coli free-form lipoprotein in the Ouchterlony immunodiffusion test. Both species of Proteus, however, gave considerably weaker precipitation lines, in comparison with the intense lines produced by the other members of the family. All of the above four bacteria outside the family Enterobacteriaceae did not cross-react with anti-E. coli lipoprotein serum. From these results, the rate of evolutionary changes in the lipoprotein gene seems to be closely related to that observed for various soluble enzymes of the Enterobacteriaceae.

Lipoprotein from Proteus mirabilis

The biosynthesis of a Proteus mirabilis outer membrane protein of molecular weight of approximately 7,000 was found to be relatively resistant to puromycin and rifampin, as is the case for the Escherichia coli liporotein. Furthermore, the existence of the lipoprotein in P. mirabilis was indicated by a comparison of the amino acid compositions of the purified free and bound forms of this protein with those of the E. coli free and bound lipoproteins.