Catalyzes the N-deacetylation of poly-beta-1,6-N-acetyl-D-glucosamine (PNAG, also referred to as PIA), a biofilm adhesin polysaccharide. N-deacetylation is crucial for attachment of the polysaccharide to the bacterial cell surface; it leads to the introduction of positive charges in the otherwise neutral PIA polymer, allowing electrostatic interactions (By similarity). Attached to the cell surface. Deletion of the icaADBCR genes leads to the inability to form biofilms, produce PIA or mediate N-acetylglucosaminyltransferase activity in vitro. Belongs to the polysaccharide deacetylase family.