title: Identification and characterization of the DNA-binding domain of the multifunctional PutA flavoenzyme.
abstract: The PutA flavoprotein from Escherichia coli is a transcriptional repressor and a bifunctional enzyme that regulates and catalyzes proline oxidation. PutA represses transcription of genes putA and putP by binding to the control DNA region of the put regulon. The objective of this study is to define and characterize the DNA binding domain of PutA. The DNA binding activity of PutA, a 1320 amino acid polypeptide, has been localized to N-terminal residues 1-261. After exploring a potential DNA-binding region and an N-terminal deletion mutant of PutA, residues 1-90 (PutA90) were determined to contain DNA binding activity and stabilize the dimeric structure of PutA. Cell-based transcriptional assays demonstrate that PutA90 functions as a transcriptional repressor in vivo. The dissociation constant of PutA90 with the put control DNA was estimated to be 110 nm, which is slightly higher than that of the PutA-DNA complex (K(d) approximately 45 nm). Primary and secondary structure analysis of PutA90 suggested the presence of a ribbon-helix-helix DNA binding motif in residues 1-47. To test this prediction, we purified and characterized PutA47. PutA47 is shown to purify as an apparent dimer, to exhibit in vivo transcriptional activity, and to bind specifically to the put control DNA. In gel-mobility shift assays, PutA47 was observed to bind cooperatively to the put control DNA with an overall dissociation constant of 15 nm for the PutA47-DNA complex. Thus, N-terminal residues 1-47 are critical for DNA-binding and the dimeric structure of PutA. These results are consistent with the ribbon-helix-helix family of transcription factors.
authors.affiliation: Department of Chemistry and Biochemistry, University of Missouri, St. Louis, Missouri 63121, USA.
authors.forename: Dan
authors.initials: D
authors.lastname: Gu
authors.forename: Yuzhen
authors.initials: Y
authors.lastname: Zhou
authors.forename: Verena
authors.initials: V
authors.lastname: Kallhoff
authors.forename: Berevan
authors.initials: B
authors.lastname: Baban
authors.forename: John J
authors.initials: JJ
authors.lastname: Tanner
authors.forename: Donald F
authors.initials: DF
authors.lastname: Becker
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D004269:DNA, Bacterial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005420:Flavoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D005420:Flavoproteins; D008565:Membrane Proteins; D009097:Multienzyme Complexes; C080683:PutA protein, Bacteria; D011994:Recombinant Proteins