5WC3

SpoIIIAG

Summary for 5WC3

• Entry DOI: 10.2210/pdb5wc3/pdb
• EMDB information: 8795
• Descriptor: SpoIIIAG, Stage III sporulation engulfment assemblyprotein (1 entity in total)
• Functional Keywords: secretion system, sporulation channel, ring building motif (rbm), protein transport
• Biological source: Bacillus subtilis BEST7613
• Total number of polymer chains: 30
• Total formula weight: 591872.58

Authors

Zeytuni, N.,Hong, C.,Worrall, L.J.,Huang, R.K.,Yu, Z.,Strynadka, N.C.J. (deposition date: 2017-06-29, release date: 2017-08-16, Last modification date: 2024-03-13)

Primary citation

Zeytuni, N.,Hong, C.,Flanagan, K.A.,Worrall, L.J.,Theiltges, K.A.,Vuckovic, M.,Huang, R.K.,Massoni, S.C.,Camp, A.H.,Yu, Z.,Strynadka, N.C.
Near-atomic resolution cryoelectron microscopy structure of the 30-fold homooligomeric SpoIIIAG channel essential to spore formation in Bacillus subtilis.
Proc. Natl. Acad. Sci. U.S.A., 114:E7073-E7081, 2017

PubMed Abstract: Bacterial sporulation allows starving cells to differentiate into metabolically dormant spores that can survive extreme conditions. Following asymmetric division, the mother cell engulfs the forespore, surrounding it with two bilayer membranes. During the engulfment process, an essential channel, the so-called feeding tube apparatus, is thought to cross both membranes to create a direct conduit between the mother cell and the forespore. At least nine proteins are required to create this channel, including SpoIIQ and SpoIIIAA-AH. Here, we present the near-atomic resolution structure of one of these proteins, SpoIIIAG, determined by single-particle cryo-EM. A 3D reconstruction revealed that SpoIIIAG assembles into a large and stable 30-fold symmetric complex with a unique mushroom-like architecture. The complex is collectively composed of three distinctive circular structures: a 60-stranded vertical β-barrel that forms a large inner channel encircled by two concentric rings, one β-mediated and the other formed by repeats of a ring-building motif (RBM) common to the architecture of various dual membrane secretion systems of distinct function. Our near-atomic resolution structure clearly shows that SpoIIIAG exhibits a unique and dramatic adaptation of the RBM fold with a unique β-triangle insertion that assembles into the prominent channel, the dimensions of which suggest the potential passage of large macromolecules between the mother cell and forespore during the feeding process. Indeed, mutation of residues located at key interfaces between monomers of this RBM resulted in severe defects both in vivo and in vitro, providing additional support for this unprecedented structure.

PubMed: 28784753
DOI: 10.1073/pnas.1704310114

Experimental method

ELECTRON MICROSCOPY (3.5 Å)