PA2196 of Pseudomonas aeruginosa is a putative transcriptional regulator and belongs to the TetR family repressor that is involved in adaptations to environmental changes and bacterial antibiotic resistance. The crystal structure of PA2196 determined to 2.4 angstrom resolution revealed nine alpha-helical bundles that can be divided into N-terminal DNA binding domain with an alpha-helix-turn-alpha-helix motif and C-terminal ligand binding domain with a hydrophobic ligand binding pocket. The distance between the N-terminal domains of homodimeric PA2196 suggested that our structure is similar to the DNA-bound form of other TetR family proteins. The C-terminal ligand binding pocket is composed mainly of hydrophobic residues and has a volume of about 523 angstrom(3) with two openings. PA2196 binds to the upstream region and can regulate the downstream genes that are chemical modification enzymes. Our crystal structure of PA2196 provides insights about the DNA recognition and ligand binding characteristics. (C) 2011 Elsevier Inc. All rights reserved.