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. Author manuscript; available in PMC: 2010 Aug 1.
Published in final edited form as: Nat Rev Microbiol. 2009 Aug;7(8):555–567. doi: 10.1038/nrmicro2182

Figure 3. The exopolysaccharide PNAG/PIA.

Figure 3

The immune evasion and biofilm aggregation exopolysaccharide PNAG/PIA, a partially de-acetylated β 1–6 linked N-acetylglucosamine homopolymer, is synthesized by the membrane-located N-acetylglucosamine transferase IcaA that needs the accessory IcaD membrane protein for activity. The growing PNAG/PIA chain is likely exported by the IcaC membrane protein. After export, the surface-located IcaB de-acetylase removes some of the N-acetyl groups, giving the polymer a cationic character that is essential for surface attachment. The Ica proteins are encoded in the ica gene locus, which contains the icaADBC operon and the icaR gene encoding a regulatory protein. Expression of the icaADBC operon is regulated either directly at the icaA promoter or via expression of IcaR by a series of global regulatory proteins. Furthermore, insertion and excision of the IS256 element may turn PNAG/PIA expression off and on.