7t8n | pdb_00007t8n
Crystal structure of the PNAG binding module PgaA-TPR 220-359
Structural highlights
Function[PGAA_ECOLI] Exports the biofilm adhesin polysaccharide poly-beta-1,6-N-acetyl-D-glucosamine (PGA) across the outer membrane. The PGA transported seems to be partially N-deacetylated since N-deacetylation of PGA by PgaB is needed for PGA export through the PgaA porin. Required for the synthesis of the beta-1,6-GlcNAc polysaccharide (PGA or poly-GlcNAc) that seems to serve as a biofilm adhesin. Publication Abstract from PubMedThe synthesis of exopolysaccharides as biofilm matrix components by pathogens is a crucial factor for chronic infections and antibiotic resistance. Many periplasmic proteins involved in polymer processing and secretion in Gram-negative synthase dependent exopolysaccharide biosynthetic systems have been individually characterized. The operons responsible for the production of PNAG, alginate, cellulose and the Pel polysaccharide each contain a gene that encodes an outer membrane associated tetratricopeptide repeat (TPR) domain containing protein. While the TPR domain has been shown to bind other periplasmic proteins, the functional consequences of these interactions for the polymer remain poorly understood. Herein, we show that the C-terminal TPR region of PgaA interacts with the de-N-acetylase domain of PgaB, and increases its deacetylase activity. Additionally, we found that when the two proteins form a complex, the glycoside hydrolase activity of PgaB is also increased. To better understand structure-function relationships we determined the crystal structure of a stable TPR module, which has a conserved groove formed by three repeat motifs. Tryptophan quenching, mass spectrometry analysis and molecular dynamics simulation studies suggest that the crystallized TPR module can bind PNAG/dPNAG via its electronegative groove on the concave surface, and potentially guide the polymer through the periplasm towards the porin for export. Our results suggest a scaffolding role for the TPR domain that combines PNAG/dPNAG translocation with the modulation of its chemical structure by PgaB. The TPR domain of PgaA is a multifunctional scaffold that binds PNAG and modulates PgaB-dependent polymer processing.,Pfoh R, Subramanian AS, Huang J, Little DJ, Forman A, DiFrancesco BR, Balouchestani-Asli N, Kitova EN, Klassen JS, Pomes R, Nitz M, Howell PL PLoS Pathog. 2022 Aug 5;18(8):e1010750. doi: 10.1371/journal.ppat.1010750., eCollection 2022 Aug. PMID:35930610[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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