Metal‐Dependent Polysaccharide Deacetylase PgaB

Abstract

PgaB is a two‐domain protein responsible for the de‐ N ‐acetylation of poly(β‐1,6‐ N ‐acetyl‐ d ‐glucosamine) ( PNAG ). Many bacteria use deacetylated PNAG ( dPNAG ) as a key extracellular matrix component. De‐ N ‐acetylation is a required modification for polymer export and biofilm formation in Escherichia coli . The N‐terminal domain adopts a (β/α) 7 fold common to the CAZy family‐4 carbohydrate esterases, and exhibits low levels of de‐ N ‐acetylation activity on PNAG oligomers. The de‐ N ‐acetylase active site contains an Asp‐His‐His metal coordination site that can bind various divalent metal cations but has optimal activity with Co 2+ , Ni 2+ , and Fe 2+ . The C‐terminal domain of PgaB adopts a (β/α) 8 fold that is structurally similar to glycoside hydrolases. This domain is proposed to bind PNAG as attempts to display hydrolytic activity have been unsuccessful, but the domain is required for de‐ N ‐acetylation in vivo. Here, we summarize recent advances in the functional characterization of PgaB: the structure, metal specificity, and progress toward inhibitor design.

The Protein BpsB Is a Poly-β-1,6-N-acetyl-d-glucosamine Deacetylase Required for Biofilm Formation in Bordetella bronchiseptica

“…Conserved Residues in BpsB Are Required for PNAG Deacetylation-Previous studies on PgaB (30,31), IcaB (35,47), Vibrio cholerae chitin deacetylase (VcCDA) (59), and PgdA (60) suggest BpsB likely uses a metal-assisted general acid/base mechanism common to CE4 members. Based on a number of substrate-bound structures of VcCDA, the metal ion is required for substrate binding and coordinating the 3Ј-hydroxyl of the GlcNAc moiety and the carbonyl of the N-acetyl group, coordinating a water molecule involved in nucleophilic attack on the N-acetyl group, and assisting in the stabilization of the tetrahedral transition state intermediate (59).…”