Functional domains of the Bacillus subtilis transcription factor AraR and identification of amino acids important for nucleoprotein complex assembly and effector binding.
The Bacillus subtilis AraR transcription factor represses at least 13 genes required for the extracellular degradation of arabinose-containing polysaccharides, transport of arabinose, arabinose oligomers, xylose, and galactose, intracellular degradation of arabinose oligomers, and further catabolism of this sugar. AraR exhibits a chimeric organization comprising a small N-terminal DNA-binding domain that contains a winged helix-turn-helix motif similar to that seen with the GntR family and a larger C-terminal domain homologous to that of the LacI/GalR family. Here, a model for AraR was derived based on the known crystal structures of the FadR and PurR regulators from Escherichia coli. We have used random mutagenesis, deletion, and construction of chimeric LexA-AraR fusion proteins to map the functional domains of AraR required for DNA binding, dimerization, and effector binding. Moreover, predictions for the functional role of specific residues were tested by site-directed mutagenesis. In vivo analysis identified particular amino acids required for dimer assembly, formation of the nucleoprotein complex, and composition of the sugar-binding cleft. This work presents a structural framework for the function of AraR and provides insight into the mechanistic mode of action of this modular repressor.
Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, Apt. 127, 2781-901 Oeiras, Portugal.
Irina Saraiva
IS
Franco
Luís Jaime
LJ
Mota
Cláudio Manuel
CM
Soares
Isabel
I
de Sá-Nogueira
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D019677:Artificial Gene Fusion; D001412:Bacillus subtilis / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D009698:Nucleoproteins / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000235:genetics; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D000099160:LexA Repressor Protein
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D009698:Nucleoproteins; D012697:Serine Endopeptidases; D014157:Transcription Factors; D000099160:LexA Repressor Protein