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 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.
Structural and Molecular Microbiology, VIB Department of Structural Biology, VIB, Pleinlaan 2, 1050 Brussels, Belgium.
Ekaterina
E
Baranova
Rémi
R
Fronzes
Abel
A
Garcia-Pino
Nani
N
Van Gerven
David
D
Papapostolou
Gérard
G
Péhau-Arnaudet
Els
E
Pardon
Jan
J
Steyaert
Stefan
S
Howorka
Han
H
Remaut
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002118:Calcium / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D020285:Cryoelectron Microscopy; D003460:Crystallization / Q000379:methods; D018360:Crystallography, X-Ray; D001411:Geobacillus stearothermophilus / Q000737:chemistry*; D007136:Immunoglobulins / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D049329:Nanostructures / Q000737:chemistry; D058105:Polymerization / Q000187:drug effects; D020836:Protein Structure, Quaternary / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000187:drug effects; D012996:Solutions
D001426:Bacterial Proteins; D007136:Immunoglobulins; D008565:Membrane Proteins; C104635:SbsB protein, Bacillus stearothermophilus; D012996:Solutions; D002118:Calcium