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

Ekatarina BARANOVA, Rémi Fronzes, Abel Garcia Pino, Nani Van Gerven, David Papapostolou, Gérard Péhau-Arnaudet, Els Pardon, Jan Steyaert, Stefan Howorka, Han Karel Remaut

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S-layers are regular two-dimensional semipermeable protein layers that constitute a major cell-wall component in archaea and many bacteria1, 2, 3. 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 applications4, 5, 6, 7. Despite their biological abundance and the technological interest in them, structural information about SLPs is limited to truncated and assembly-negative proteins8, 9, 10. 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 ?-shaped disk-like monomeric crystallization unit stabilized by interdomain Ca2+ ion coordination. A Ca2+-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 biotechnology4, 5, 6, 7.
Original languageEnglish
Pages (from-to)119-122
Number of pages4
Publication statusPublished - 10 Jun 2012


  • S-layer
  • Structural Biology


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