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Macrophages recognize and adhere to an OmpD-like protein of Salmonella typhimurium
1Department of Microbiology, University of New Hampshire, Durham 03824-2617, USA. robert.negm@unh.edu
Abstract:
Murine peritoneal macrophages bind to Salmonella typhimurium in vitro in the absence of exogenous opsonins. We have identified an outer membrane protein of S. typhimurium that mediates this adhesion. Biotin-labeled macrophages were used to probe electroblotted envelope proteins of S. typhimurium that had been previously resolved by polyacrylamide electrophoresis under denaturing and reducing conditions. Macrophages bound to an outer membrane protein with an apparent molecular mass of 44 kDa. The protein was purified to homogeneity and free of detectable lipopolysaccharide. Limited microsequencing of this protein resulted in a 15-amino acid query sequence of A-E-V-Y-N-K-D-G-N-K-L-D-L-Y-G, which shares complete identity with a 15-mer of both the OmpD of S. typhimurium SH 7454 and the OmpC polypeptide of Escherichia coli K-12. Picomolar concentrations of this purified protein significantly inhibited the subsequent adherence of 35S-labeled S. typhimurium to macrophages in monolayers. We propose that this 44-kDa protein is involved in the recognition of S. typhimurium by macrophage during the initial stages of infection.
Insights
Salmonella typhimurium outer membrane protein (OMP) mediates macrophage adhesion. This 44-kDa OMP, identified as OmpD, is crucial for bacterial recognition by macrophages during infection.
Area of Science:
- Microbiology
- Immunology
- Bacterial Pathogenesis
Background:
- Murine peritoneal macrophages exhibit in vitro binding to Salmonella typhimurium without external opsonins.
- This adhesion suggests a direct interaction mediated by bacterial surface components.
Purpose of the Study:
- To identify the specific outer membrane protein of S. typhimurium responsible for macrophage adhesion.
- To characterize the role of this protein in the initial stages of bacterial-macrophage interaction.
Main Methods:
- Utilized biotin-labeled macrophages to probe S. typhimurium envelope proteins separated by SDS-PAGE.
- Purified the identified 44-kDa outer membrane protein.
- Performed microsequencing and compared the resulting peptide sequence to known bacterial proteins.
- Assessed the inhibitory effect of the purified protein on bacterial adherence to macrophage monolayers.
Main Results:
- Macrophages specifically bound to a 44-kDa outer membrane protein of S. typhimurium.
- Microsequencing revealed the protein's identity as OmpD, sharing homology with E. coli OmpC.
- Purified OmpD inhibited S. typhimurium adherence to macrophages at picomolar concentrations.
Conclusions:
- A 44-kDa outer membrane protein, OmpD, mediates the adhesion of S. typhimurium to murine macrophages.
- This protein plays a significant role in the initial recognition of S. typhimurium by macrophages.
- OmpD is a key factor in the early stages of S. typhimurium infection.