SbsB structure and lattice reconstruction unveil Ca2+ triggered S-layer assembly

Area of Science:

• Microbiology
• Structural Biology
• Biotechnology

Background:

• S-layers are protein shells found in bacteria and archaea, crucial for cell wall structure and function.
• Their regular, self-assembling nature makes S-layer proteins (SLPs) promising for nanotechnology applications.
• Limited structural data exists for full-length, assembly-competent SLPs.

Purpose of the Study:

• To determine the X-ray structure of the SbsB SLP from Geobacillus stearothermophilus PV72/p2.
• To elucidate the molecular mechanisms underlying SLP self-assembly into S-layer lattices.
• To provide insights for designing novel bio-inspired nanomaterials.

Main Methods:

• Nanobody-aided X-ray crystallography was employed to obtain the SbsB structure.
• Ca(2+) ion coordination was analyzed for its role in protein structure and assembly.
• Cryo-electron microscopy and chemical crosslinking data were integrated to model the S-layer lattice.

Main Results:

• The SbsB protein comprises seven domains, including a cell-wall attachment domain and six immunoglobulin-like domains.
• A Ca(2+)-dependent conformational change was identified, enabling the protein to form a condensed quaternary structure.
• A structural model of the SbsB lattice as a porous protein sheet was proposed.

Conclusions:

• The determined SbsB structure provides a novel model for protein assemblies and S-layer formation.
• Understanding SbsB's self-assembly mechanism advances knowledge of SLP physiology.
• This work facilitates the rational design of engineered protein structures for biotechnological applications.