Molecular insights into phosphoethanolamine cellulose formation and secretion

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Phosphoethanolamine (pEtN) cellulose is a modified cellulose produced by Enterobacteriaceae.
• The E. coli cellulose synthase complex (BcsA, BcsB, BcsC) mediates cellulose synthesis and outer membrane translocation.
• The roles of BcsG (pEtN transferase) and BcsZ (cellulase) in pEtN cellulose modification and secretion remain unclear.

Approach:

• Investigated the roles of BcsA, BcsG, BcsC, and BcsZ in pEtN cellulose secretion.
• Utilized protein engineering to explore pEtN cellulose biosynthesis in orthogonal systems.
• Examined the interaction between BcsA's N-terminal domain and BcsG, and BcsB's interaction with BcsC.

Key Points:

• The N-terminal domain of BcsA positions BcsG near the cellulose polymer.
• BcsB tethers BcsC to form a trans-envelope secretion system, with BcsC binding cello-oligosaccharides.
• BcsZ's hydrolytic activity, not the subunit itself, is crucial for secretion, suggesting a mechanism involving enzymatic removal of mislocalized cellulose.

Conclusions:

• Elucidated the mechanism of pEtN cellulose secretion across the E. coli cell envelope.
• Demonstrated that BcsZ's cellulase activity facilitates secretion.
• Successfully engineered pEtN modification into other cellulose biosynthetic systems.