Our data suggest that this loop is required for membraneĪssociation and likely anchors IcaB to the membrane during polysaccharide biosynthesis. Hydrophobic loop found only in Gram-positive homologues of IcaB. Furthermore, we identified a conserved surface-exposed Mutational analysis of conserved active site residues suggests that IcaB uses an alteredĬatalytic mechanism in comparison to other characterized CE4 members.
The absence of these residues in PgaB provides a rationale for the requirement of a C-terminal domain for efficient deacetylation From docking studies with β-1,6-GlcNAc oligomers and structural comparison to PgaB from Escherichia coli, the Gram-negative homologue of IcaB, we identify Arg-45, Tyr-67, and Trp-180 as key residues for PNAG binding during catalysis. Of IcaBAd is similar to most CE4s showing the maximum rates of de-N-acetylation with Ni2+, Co2+, and Zn2+. The structure of IcaBAd reveals a (β/α)7 barrel common to the family four carbohydrate esterases (CE4s) with the canonical motifs circularly permuted. To understand the molecular basisįor PNAG de-N-acetylation, the structure of IcaB from Ammonifex degensii (IcaBAd) has been determined to 1.7 Å resolution. Partial de-N-acetylation of the exopolysaccharide poly-β-1,6-N-acetyl-d-glucosamine (PNAG) by the extracellular protein IcaB is required for biofilm formation. Exopolysaccharides are required for the development and integrity of biofilms produced by a wide variety of bacteria.
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