Characterization of the hca cluster encoding the dioxygenolytic pathway for initial catabolism of 3-phenylpropionic acid in Escherichia coli K-12.
We have identified, cloned, and sequenced the hca cluster encoding the dioxygenolytic pathway for initial catabolism of 3-phenylpropionic acid (PP) in Escherichia coli K-12. This cluster maps at min 57.5 of the chromosome and is composed of five catabolic genes arranged as a putative operon (hcaA1A2CBD) and two additional genes transcribed in the opposite direction that encode a potential permease (hcaT) and a regulator (hcaR). Sequence comparisons revealed that while hcaA1A2CD genes encode the four subunits of the 3-phenylpropionate dioxygenase, the hcaB gene codes for the corresponding cis-dihydrodiol dehydrogenase. This type of catabolic module is homologous to those encoding class IIB dioxygenases and becomes the first example of such a catabolic cluster in E. coli. The inducible expression of the hca genes requires the presence of the hcaR gene product, which acts as a transcriptional activator and shows significant sequence similarity to members of the LysR family of regulators. Interestingly, the HcaA1A2CD and HcaB enzymes are able to oxidize not only PP to 3-(2,3-dihydroxyphenyl)propionate (DHPP) but also cinnamic acid (CI) to its corresponding 2, 3-dihydroxy derivative. Further catabolism of DHPP requires the mhp-encoded meta fission pathway for the mineralization of 3-hydroxyphenylpropionate (3HPP) (A. Ferrández, J. L. García, and E. Díaz, J. Bacteriol. 179:2573-2581, 1997). Expression in Salmonella typhimurium of the mhp genes alone or in combination with the hca cluster allowed the growth of the recombinant bacteria in 3-hydroxycinnamic acid (3HCI) and CI, respectively. Thus, the convergent mhp- and hca-encoded pathways are also functional in S. typhimurium, and they are responsible for the catabolism of different phenylpropanoid compounds (3HPP, 3HCI, PP, and CI) widely available in nature.
Díaz
E
E
Department of Molecular Microbiology, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, 28006 Madrid, Spain. cibdf4f@fresno.csic.es
Ferrández
A
A
García
J L
JL
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D000090702:Constitutive Androstane Receptor; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000235:genetics; D008956:Models, Chemical; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D027361:Organic Anion Transporters; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010105:Oxygenases / Q000235:genetics* / Q000378:metabolism; D010666:Phenylpropionates / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics; D015183:Restriction Mapping; D017422:Sequence Analysis, DNA; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors
D000090702:Constitutive Androstane Receptor; D029968:Escherichia coli Proteins; C112604:HcaB protein, E coli; C112605:HcaT protein, E coli; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; D010666:Phenylpropionates; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D014157:Transcription Factors; C035253:3-phenylpropionic acid; D010088:Oxidoreductases; D010105:Oxygenases; C112603:3-phenylpropionate dioxygenase