1.B.55 The Poly Acetyl Glucosamine Porin (PgaA) Family
The linear homopolymer poly-beta-1,6-N-acetyl-D-glucosamine (beta-1,6-GlcNAc; PGA) serves as an adhesin for the maintenance of biofilm structural stability in diverse eubacteria. Its function in Escherichia coli K-12 requires the gene products of the pgaABCD operon, all of which are necessary for biofilm formation. PgaC is an apparent glycosyltransferase that is required for PGA synthesis, and PgaD is also needed for PGA formation. Deletion of genes for the predicted outer membrane proteins PgaA and PgaB did not prevent PGA synthesis but did block its export at the cell poles, the initial attachment site for biofilm formation (Itoh et al., 2008). PgaA contains a predicted beta-barrel porin and a superhelical domain containing tetratricopeptide repeats, which may mediate protein-protein interactions. It may form the outer membrane secretin for PGA. PgaB contains predicted carbohydrate binding and polysaccharide N-deacetylase domains. Overexpression of pgaB increases the primary amine content (glucosamine) of PGA. Site-directed mutations targeting the N-deacetylase catalytic activity of PgaB blocked PGA export and biofilm formation, implying that N-deacetylation promotes PGA export through the PgaA porin.
The generalized reaction catalyzed by PgaA is:
deacetylated PGA (periplasm) → deacetylated PGA (cell surface)