4p7r
Structure of Escherichia coli PgaB C-terminal domain in complex with a poly-beta-1,6-N-acetyl-D-glucosamine (PNAG) hexamer
Structural highlights
FunctionPGAB_ECOLI Catalyzes the N-deacetylation of poly-beta-1,6-N-acetyl-D-glucosamine (PGA), a biofilm adhesin polysaccharide. N-deacetylation promotes PGA export through the PgaA porin.[1] [2] Publication Abstract from PubMedPoly-beta-1,6-N-acetyl-d-glucosamine (PNAG) is an exopolysaccharide produced by a wide variety of medically important bacteria. Polyglucosamine subunit B (PgaB) is responsible for the de-N-acetylation of PNAG, a process required for polymer export and biofilm formation. PgaB is located in the periplasm and likely bridges the inner membrane synthesis and outer membrane export machinery. Here, we present structural, functional, and molecular simulation data that suggest PgaB associates with PNAG continuously during periplasmic transport. We show that the association of PgaB's N- and C-terminal domains forms a cleft required for the binding and de-N-acetylation of PNAG. Molecular dynamics (MD) simulations of PgaB show a binding preference for N-acetylglucosamine (GlcNAc) to the N-terminal domain and glucosammonium to the C-terminal domain. Continuous ligand binding density is observed that extends around PgaB from the N-terminal domain active site to an electronegative groove on the C-terminal domain that would allow for a processive mechanism. PgaB's C-terminal domain (PgaB310-672) directly binds PNAG oligomers with dissociation constants of approximately 1-3 mM, and the structures of PgaB310-672 in complex with beta-1,6-(GlcNAc)6, GlcNAc, and glucosamine reveal a unique binding mode suitable for interaction with de-N-acetylated PNAG (dPNAG). Furthermore, PgaB310-672 contains a beta-hairpin loop (betaHL) important for binding PNAG that was disordered in previous PgaB42-655 structures and is highly dynamic in the MD simulations. We propose that conformational changes in PgaB310-672 mediated by the betaHL on binding of PNAG/dPNAG play an important role in the targeting of the polymer for export and its release. Modification and periplasmic translocation of the biofilm exopolysaccharide poly-beta-1,6-N-acetyl-d-glucosamine.,Little DJ, Li G, Ing C, DiFrancesco BR, Bamford NC, Robinson H, Nitz M, Pomes R, Howell PL Proc Natl Acad Sci U S A. 2014 Jul 3. pii: 201406388. PMID:24994902[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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