Structural analysis and evidence for dynamic emergence of Bacillus anthracis S-layer networks

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Surface layers (S-layers) are crystalline protein arrays on Bacteria and Archaea.
• Bacillus anthracis, the anthrax bacterium, produces two main surface proteins: Sap and EA1.
• These proteins appear sequentially and can form S-layer arrays.

Purpose of the Study:

• To determine the structural parameters of S-layers formed by Sap and EA1 in Bacillus anthracis.
• To investigate the arrangement and potential interactions of these S-layer proteins.
• To understand how the emergence of EA1 affects the Sap S-layer.

Main Methods:

• Computer image processing of electron micrographs of S-layer fragments and whole bacteria.
• Calculation of projection maps for Sap and EA1 using p1 symmetry.
• Freeze-etching experiments to analyze S-layer configurations.

Main Results:

• The unit cell parameters for EA1 were determined as a=69 Å, b=83 Å, γ=106°.
• The unit cell parameters for Sap were determined as a=184 Å, b=81 Å, γ=84°.
• Data suggests different arrangements (settings) for EA1 and Sap S-layers, with EA1 emergence destabilizing the Sap S-layer.

Conclusions:

• Bacillus anthracis S-layers composed of Sap and EA1 have distinct structural characteristics.
• The sequential appearance and interaction of these proteins influence S-layer organization.
• EA1's emergence can disrupt the stability of the Sap S-layer, impacting surface structure.