9FMT

Cryo-EM structure of the BcsB hexameric crown from the E. coli cellulose secretion macrocomplex

Summary for 9FMT

• Entry DOI: 10.2210/pdb9fmt/pdb
• EMDB information: 50567
• Descriptor: Cyclic di-GMP-binding protein (1 entity in total)
• Functional Keywords: bacterial cellulose secretion, membrane protein
• Biological source: Escherichia coli
• Total number of polymer chains: 6
• Total formula weight: 500075.06

Authors

Anso, I.,Krasteva, P.V. (deposition date: 2024-06-07, release date: 2024-10-16, Last modification date: 2024-11-06)

Primary citation

Anso, I.,Zouhir, S.,Sana, T.G.,Krasteva, P.V.
Structural basis for synthase activation and cellulose modification in the E. coli Type II Bcs secretion system.
Nat Commun, 15:8799-8799, 2024

PubMed Abstract: Bacterial cellulosic polymers constitute a prevalent class of biofilm matrix exopolysaccharides that are synthesized by several types of bacterial cellulose secretion (Bcs) systems, which include conserved cyclic diguanylate (c-di-GMP)-dependent cellulose synthase modules together with diverse accessory subunits. In E. coli, the biogenesis of phosphoethanolamine (pEtN)-modified cellulose relies on the BcsRQABEFG macrocomplex, encompassing inner-membrane and cytosolic subunits, and an outer membrane porin, BcsC. Here, we use cryogenic electron microscopy to shed light on the molecular mechanisms of BcsA-dependent recruitment and stabilization of a trimeric BcsG pEtN-transferase for polymer modification, and a dimeric BcsF-dependent recruitment of an otherwise cytosolic BcsERQ regulatory complex. We further demonstrate that BcsE, a secondary c-di-GMP sensor, can remain dinucleotide-bound and retain the essential-for-secretion BcsRQ partners onto the synthase even in the absence of direct c-di-GMP-synthase complexation, likely lowering the threshold for c-di-GMP-dependent synthase activation. Such activation-by-proxy mechanism could allow Bcs secretion system activity even in the absence of substantial intracellular c-di-GMP increase, and is reminiscent of other widespread synthase-dependent polysaccharide secretion systems where dinucleotide sensing and/or synthase stabilization are carried out by key co-polymerase subunits.

PubMed: 39394223
DOI: 10.1038/s41467-024-53113-8

Experimental method

ELECTRON MICROSCOPY (2.35 Å)