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Electron microscopy of the major outer membrane protein of Campylobacter jejuni
1Department of Bacteriology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Abstract:
The surfaces of the disrupted-cell surfaces of the Campylobacter jejuni strains FUM158432 and M1 were examined using the negative-staining technique and electron microscopy. The surfaces of the whole cells and the outer membranes were covered with small dark dots which, in some areas, were arranged in hexagonal patterns. The hexagonal arrangement was more clearly seen in extracted outer membrane. The size of each structure was measured based on a center-to-center distance with the adjacent structure, and was determined to be 9.9 +/- 0.9 nm. A profile of the proteins in the outer membrane by SDS-PAGE, performed in 0.1% SDS and at 100 C, showed 42 kDa proteins to comprise the major outer membrane protein of this bacterium. Digestion of the outer membrane materials with proteinase reduced this protein band in the SDS-PAGE, and the amount of dark dots on the electron micrograph indicated the structure to be the major outer membrane protein (porin) of this bacterium. The power spectrogram of a computer-assisted Fourier transformation of the hexagonally arranged porin proteins suggests that the porin has a trimeric structure rather than a monomeric one.
Insights
This study reveals Campylobacter jejuni outer membranes possess hexagonal arrays of porin proteins. Electron microscopy and SDS-PAGE confirm these porins likely form trimeric structures, crucial for bacterial outer membrane function.
Area of Science:
- Microbiology
- Structural Biology
- Biophysics
Background:
- Campylobacter jejuni is a significant foodborne pathogen.
- Understanding the structure of bacterial outer membranes is key to developing novel antimicrobial strategies.
Purpose of the Study:
- To characterize the surface structures of Campylobacter jejuni outer membranes.
- To determine the structural organization and nature of the major outer membrane proteins.
Main Methods:
- Negative-staining electron microscopy of whole cells and extracted outer membranes.
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to profile outer membrane proteins.
- Proteinase K digestion to identify protein components.
- Computer-assisted Fourier transformation and power spectrogram analysis.
Main Results:
- Hexagonal arrays of protein structures, approximately 9.9 nm apart, were observed on Campylobacter jejuni outer membranes.
- SDS-PAGE identified a 42 kDa protein as the major outer membrane protein.
- Proteinase K digestion reduced the intensity of the 42 kDa band and the observed surface dots, confirming it as porin.
- Fourier analysis suggested a trimeric structure for the porin proteins.
Conclusions:
- Campylobacter jejuni outer membranes are organized with hexagonally packed porin proteins.
- The major outer membrane protein of Campylobacter jejuni is likely a porin with a trimeric structure.
- These findings provide insights into the structural basis of Campylobacter jejuni outer membrane integrity and function.