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Three-dimensional structure of the surface protein layer (MW layer) of Bacillus brevis 47
A Tsuboi1, H Engelhardt, U Santarius
1Max-Planck-Institut für Biochemie, Martinsried, Federal Republic of Germany.
Abstract:
The three-dimensional (3D) structure of one surface protein layer from Bacillus brevis 47, the middle wall (MW) layer, has been reconstructed from tilted-view electron micrographs after correlation averaging to a resolution of 2 nm. The MW layer has p6 symmetry with a center-to-center spacing of 18.3 nm and a minimum thickness of 5.5 nm. The reconstruction reveals a distinct domain structure: the heavier domain of six monomers jointly forms a massive core centered at the sixfold symmetry axis, and lighter domains interconnect adjacent unit cells. In addition, the larger domains collectively form a pore by making contact with each other towards the inner surface, while the smaller domains establish a second connectivity towards the outer surface of the S layer. The MW layer of B. brevis resembles the S layer of Acetogenium kivui in various aspects: they have very similar lattice parameters and highly reminiscent 3D structures; the pores penetrate through the whole core and appear to determine the porosity of the S layers.
Insights
The 3D structure of Bacillus brevis 47's middle wall (MW) layer was resolved to 2 nm. This surface protein layer features a unique domain structure forming pores, similar to Acetogenium kivui's S layer.
Area of Science:
- Microbiology
- Structural Biology
- Biophysics
Background:
- Surface protein layers (S layers) are common in prokaryotes.
- The middle wall (MW) layer of Bacillus brevis 47 is a type of S layer.
- Understanding S layer structure is crucial for cell envelope function.
Purpose of the Study:
- To determine the 3D structure of the Bacillus brevis 47 MW layer.
- To elucidate the structural organization and domain arrangement.
- To compare the MW layer structure with other known S layers.
Main Methods:
- Three-dimensional reconstruction from tilted-view electron micrographs.
- Correlation averaging for high-resolution structural analysis.
- Analysis of symmetry, lattice parameters, and domain morphology.
Main Results:
- The MW layer was reconstructed to a 2 nm resolution, exhibiting p6 symmetry.
- A distinct domain structure was revealed, with monomers forming a central core and interconnecting lighter domains.
- Pores were identified, penetrating the core and contributing to layer porosity, similar to Acetogenium kivui.
Conclusions:
- The 3D structure of the B. brevis 47 MW layer provides insights into S layer architecture.
- The identified domain structure and pore formation are key features of this surface protein layer.
- Structural similarities suggest conserved functional roles for S layers across different bacterial species.