Tetralin-induced and ThnR-regulated aldehyde dehydrogenase and beta-oxidation genes in Sphingomonas macrogolitabida strain TFA.
A new cluster of genes has been found downstream of the previously identified thnA2 gene. The gene products are similar to nonacylating aldehyde dehydrogenases (ThnG) and to proteins representing a complete beta-oxidation pathway (ThnH to ThnP). ThnG has a nonacylating NAD-dependent pimelic semialdehyde dehydrogenase activity that renders pimelic acid a seven-carbon dicarboxylic acid. For further metabolism via beta-oxidation, pimelic acid could be acylated by a constitutive acyl coenzyme A (acyl-CoA) ligase found in Sphingomonas macrogolitabida strain TFA or by ThnH, which would transfer CoA from a previously acylated molecule. The first round of beta-oxidation is expected to render glutaryl-CoA and acetyl-CoA. Glutaryl-CoA dehydrogenase (ThnN) would catalyze the oxidation and decarboxylation of glutaryl-CoA and yield crotonyl-CoA, which enters the central metabolism via acetyl-CoA. Mutagenesis studies have shown that these genes are not essential for growth on tetralin or fatty acids, although a thnG disruption mutant showed threefold less pimelic semialdehyde dehydrogenase activity. Transcriptional analysis indicated that these genes are induced by tetralin, subjected to catabolite repression, and regulated by the same regulatory factors previously identified to regulate other thn structural genes. In the present study, transcription initiation upstream of thnH and thnM has been detected by primer extension analysis, and putative promoters were identified by sequence analysis. In addition, binding of the activator ThnR to its putative binding sites at the PH and PM promoter regions has been characterized. These results provide a complete characterization of the biodegradation pathway of tetralin to central metabolites and describe the transcriptional organization of the thn operons in S. macrogolitabida strain TFA.
López-Sánchez
Aroa
A
Centro Andaluz de Biología del Desarrollo, CSIC-Universidad Pablo de Olavide, Carretera de Utrera Km 1, 41013 Seville, Spain.
Floriano
Belén
B
Andújar
Eloisa
E
Hernáez
Maria José
MJ
Santero
Eduardo
E
D000444:Aldehyde Dehydrogenase / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024202:Electrophoretic Mobility Shift Assay; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D023061:Gene Order; D005798:Genes, Bacterial; D053858:Metabolic Networks and Pathways / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family; D010084:Oxidation-Reduction; D010867:Pimelic Acids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D020578:Sphingomonas / Q000201:enzymology* / Q000378:metabolism*; D013764:Tetrahydronaphthalenes / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D024363:Transcription Initiation Site
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D010867:Pimelic Acids; D013764:Tetrahydronaphthalenes; D014157:Transcription Factors; D000444:Aldehyde Dehydrogenase; C095210:tetralin