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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)

References associated with 1.B.55 family:

Cerca, N. and K.K. Jefferson. (2008). Effect of growth conditions on poly-N-acetylglucosamine expression and biofilm formation in Escherichia coli. FEMS Microbiol. Lett. 283: 36-41. 18445167
Itoh, Y., J.D. Rice, C. Goller, A. Pannuri, J. Taylor, J. Meisner, T.J. Beveridge, J.F. Preston, 3rd, and T. Romeo. (2008). Roles of pgaABCD genes in synthesis, modification, and export of the Escherichia coli biofilm adhesin poly-β-1,6-N-acetyl-D-glucosamine. J. Bacteriol. 190: 3670-3680. 18359807
Kenedy MR., Luthra A., Anand A., Dunn JP., Radolf JD. and Akins DR. (2014). Structural modeling and physicochemical characterization provide evidence that P66 forms a beta-barrel in the Borrelia burgdorferi outer membrane. J Bacteriol. 196(4):859-72. 24317399
Zogaj, X., M. Nimtz, M. Rohde, W. Bokranz, and U. Römling. (2001). The multicellular morphotypes of Salmonella typhimurium and Escherichia coli produce cellulose as the second component of the extracellular matrix. Mol. Microbiol. 39: 1452-1463. 11260463