Conserved Motifs in the Ligand-Binding Domain of TetR Family Regulators: Identification and Analysis.

TetR family regulators (TFRs) represent one of the largest and most extensively studied groups of bacterial transcription factors. TFRs contain 2 domains, a conserved N-terminal DNA binding domain and a remarkably variable C-terminal domain (CTD). This structural diversity enables TFRs to recognize a wide range of effectors and regulate numerous processes in bacterial cells. In this study, we identified conserved sequence motifs within the TFR CTDs. We checked these motifs against sequences of the well-characterized TFRs and compiled them into organized data files, which enable direct motif searches in newly characterized TFRs. The detailed motif analysis of 10 TFR representatives revealed that most residues involved in ligand binding exhibit high conservation, with some exceptions in TFRs related to multidrug resistance. Motif mapping onto the CTD structures showed their presence not only in helices α5 to α7 of the central triangle but also in helices α4 or α8 to α9, depending on ligand-binding cavity location. Motifs were also converted into the Prosite patterns for broader usability. Finally, homolog searches across bacterial families indicated a wide distribution of motifs associated with antibiotic and multidrug resistance. These findings provide practical tools for prediction of putative TFR function and may support antimicrobial drug development.