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Structure of the hexagonal surface layer on Caulobacter crescentus cells.
Tanmay A M Bharat1,2, Danguole Kureisaite-Ciziene1, Gail G Hardy3
1Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
Nature Microbiology
|April 19, 2017
Summary
This study reveals the atomic structure of bacterial surface layers (S-layers) using X-ray crystallography and cryo-electron tomography. The findings detail the porous S-layer lattice structure and its stabilization by calcium ions.
Area of Science:
- Microbiology
- Structural Biology
- Biophysics
Background:
- Prokaryotic cells often possess a surface layer (S-layer) composed of repeating S-layer proteins.
- S-layers are crucial for cell protection, mechanical stability, and pathogenicity.
- In situ structural data of S-layers has been limited, hindering understanding of their arrangement.
Purpose of the Study:
- To determine the atomic-level structure of the S-layer in Caulobacter crescentus.
- To elucidate the in vivo arrangement and structural features of the S-layer protein RsaA.
- To bridge the gap between atomic resolution structures and cellular context.
Main Methods:
- X-ray crystallography of purified Caulobacter crescentus RsaA protein.
- Electron cryotomography and sub-tomogram averaging of S-layer on cell stalks.
- Docking of the high-resolution X-ray structure into the cryo-electron tomography map.
Main Results:
- A 2.7 Å X-ray structure of the hexameric S-layer lattice was obtained.
- A 7.4 Å structure of the in vivo S-layer was determined.
- The combined approach yielded a pseudo-atomic model of the cellular S-layer, revealing a porous structure with 27 Å gaps.
- Multiple Ca2+ ions were identified stabilizing the S-layer lattice.
Conclusions:
- The study provides the first pseudo-atomic resolution structure of an in vivo S-layer.
- The findings reveal the porous nature and stabilization mechanisms of bacterial S-layers.
- This work integrates structural data across multiple scales, from atoms to cells.