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

S-layers are regular two-dimensional semipermeable protein layers that constitute a major cell-wall component in archaea and many bacteria. The nanoscale repeat structure of the S-layer lattices and their self-assembly from S-layer proteins (SLPs) have sparked interest in their use as patterning and...

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Published in:Nature (London) 2012-07, Vol.487 (7405), p.119-122
Main Authors: BARANOVA, Ekaterina, FRONZES, Remi, GARCIA-PINO, Abel, VAN GERVEN, Nani, PAPAPOSTOLOU, David, PEHAU-ARNAUDET, Gerard, PARDON, Els, STEYAERT, Jan, HOWORKA, Stefan, REMAUT, Han
Format: Article
Language:English
Subjects:
Bacterial Proteins - chemistry
Bacterial Proteins - metabolism
Biological and medical sciences
Calcium - chemistry
Calcium - metabolism
Calcium - pharmacology
Cryoelectron Microscopy
Crystalline structure
Crystallization - methods
Crystallography, X-Ray
Fundamental and applied biological sciences. Psychology
Geobacillus stearothermophilus - chemistry
Immunoglobulins - chemistry
Membrane Proteins - chemistry
Membrane Proteins - metabolism
Models, Molecular
Molecular biophysics
Molecular Dynamics Simulation
Nanostructures - chemistry
Polymerization - drug effects
Protein Structure, Quaternary - drug effects
Protein Structure, Tertiary - drug effects
Solutions
Structure in molecular biology
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Summary:S-layers are regular two-dimensional semipermeable protein layers that constitute a major cell-wall component in archaea and many bacteria. The nanoscale repeat structure of the S-layer lattices and their self-assembly from S-layer proteins (SLPs) have sparked interest in their use as patterning and display scaffolds for a range of nano-biotechnological applications. Despite their biological abundance and the technological interest in them, structural information about SLPs is limited to truncated and assembly-negative proteins. Here we report the X-ray structure of the SbsB SLP of Geobacillus stearothermophilus PV72/p2 by the use of nanobody-aided crystallization. SbsB consists of a seven-domain protein, formed by an amino-terminal cell-wall attachment domain and six consecutive immunoglobulin-like domains, that organize into a φ-shaped disk-like monomeric crystallization unit stabilized by interdomain Ca(2+) ion coordination. A Ca(2+)-dependent switch to the condensed SbsB quaternary structure pre-positions intermolecular contact zones and renders the protein competent for S-layer assembly. On the basis of crystal packing, chemical crosslinking data and cryo-electron microscopy projections, we present a model for the molecular organization of this SLP into a porous protein sheet inside the S-layer. The SbsB lattice represents a previously undescribed structural model for protein assemblies and may advance our understanding of SLP physiology and self-assembly, as well as the rational design of engineered higher-order structures for biotechnology.
ISSN:0028-0836
1476-4687
DOI:10.1038/nature11155