HbpR, a new member of the XylR/DmpR subclass within the NtrC family of bacterial transcriptional activators, regulates expression of 2-hydroxybiphenyl metabolism in Pseudomonas azelaica HBP1.
The regulation of 2-hydroxybiphenyl and 2,2'-dihydroxybiphenyl degradation in Pseudomonas azelaica is mediated by the regulatory gene, hbpR. The hbpR gene encodes a 63-kDa protein belonging to the NtrC family of prokaryotic transcriptional activators and having the highest homology to members of the XylR/DmpR subclass. Disruption of the hbpR gene in P. azelaica and complementation in trans showed that the HbpR protein was the key regulator for 2-hydroxybiphenyl metabolism. Induction experiments with P. azelaica and Escherichia coli containing luxAB-based transcriptional fusions revealed that HbpR activates transcription from a promoter (P(hbpC)) in front of the first gene for 2-hydroxybiphenyl degradation, hbpC, and that 2-hydroxybiphenyl itself is the direct effector for HbpR-mediated activation. Of several compounds tested, only the pathway substrates 2-hydroxybiphenyl and 2,2'-dihydroxybiphenyl and structural analogs like 2-aminobiphenyl and 2-hydroxybiphenylmethane were effectors for HbpR activation. HbpR is therefore, to our knowledge, the first regulator of the XylR/DmpR class that recognizes biaromatic but not monoaromatic structures. Analysis of a spontaneously occurring mutant, P. azelaica HBP1 Prp, which can grow with the non-wild-type effector 2-propylphenol, revealed a single mutation in the hbpR gene (T613C) leading to a Trp-->Arg substitution at amino acid residue 205. P. azelaica HBP1 derivative strains without a functional hbpR gene constitutively expressed the genes for 2-hydroxybiphenyl degradation when complemented in trans with the hbpR-T613C gene. This suggests the importance of this residue, which is conserved among all members of the XylR/DmpR subclass, for interdomain repression.
Jaspers
M C
MC
Swiss Federal Institute for Environmental Science and Technology, CH-8600 Dübendorf, Switzerland.
Suske
W A
WA
Schmid
A
A
Goslings
D A
DA
Kohler
H P
HP
van der Meer
J R
JR
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001713:Biphenyl Compounds / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009154:Mutation; D051922:PII Nitrogen Regulatory Proteins; D010636:Phenols / Q000378:metabolism; D011549:Pseudomonas / Q000235:genetics*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*
D001426:Bacterial Proteins; D001713:Biphenyl Compounds; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C403328:HbpR protein, Pseudomonas azelaica; D051922:PII Nitrogen Regulatory Proteins; D010636:Phenols; D015534:Trans-Activators; D014157:Transcription Factors; C497876:glnG protein, E coli; C080638:2-propylphenol; C004369:2-phenylphenol