Purification and characterization of muconate cycloisomerase from aniline-assimilating Rhodococcus erythropolis AN-13

Constitutive expression of catABC genes in the aniline-assimilating bacterium Rhodococcus species AN-22: production, purification, characterization and gene analysis of CatA, CatB and CatC

The aniline-assimilating bacterium Rhodococcus sp. AN-22 was found to constitutively synthesize CatB (cis,cis-muconate cycloisomerase) and CatC (muconolactone isomerase) in its cells growing on non-aromatic substrates, in addition to the previously reported CatA (catechol 1,2-dioxygenase). The bacterium maintained the specific activity of the three enzymes at an almost equal level during cultivation on succinate. CatB and CatC were purified to homogeneity and characterized. CatB was a monomer with a molecular mass of 44 kDa. The enzyme was activated by Mn2+, Co2+ and Mg2+. Native CatC was a homo-octamer with a molecular mass of 100 kDa. The enzyme was stable between pH 7.0 and 10.5 and was resistant to heating up to 90 degrees C. Genes coding for CatA, CatB and CatC were cloned and named catA, catB and catC respectively. The catABC genes were transcribed as one operon. The deduced amino acid sequences of CatA, CatB and CatC showed high identities with those from other Gram-positive micro-organisms. A regulator gene such as catR encoding a regulatory protein was not observed around the cat gene cluster of Rhodococcus sp. AN-22, but a possible relic of catR was found in the upstream region of catA. Reverse transcriptase-PCR and primer extension analyses showed that the transcriptional start site of the cat gene cluster was located 891 bp upstream of the catA initiation codon in the AN-22 strain growing on both aniline and succinate. Based on these data, we concluded that the bacterium constitutively transcribed the catABC genes and translated its mRNA into CatA, CatB and CatC.

Purification, characterization, and gene cloning of cis,cis-muconate cycloisomerase from benzamide-assimilating Arthrobacter sp. BA-5-17

cis,cis-Muconate cycloisomerase (MC) was purified to homogeneity from benzamide-assimilating Arthrobacter sp. BA-5-17. The purified enzyme showed high activities for cis,cis-muconate and 3-methyl-cis,cis-muconate, and preferred the 3-substituted derivatives over the derivatives with the same substituent at the 2 position as a substrate. A gene encoding MC of strain BA-5-17 was cloned and named catB. The catB gene was clustered with catR encoding a putative LysR-type regulator, catC encoding a putative muconolactone isomerase, and catA-II encoding the catechol 1,2-dioxygenase isozymes CD-III-1 and III-2. These genes showed the same orientation in transcriptional direction and the organization of cloned genes was catRBCA-II. In the phylogenetic analysis of MCs and chloro-MCs, the BA-5-17 and Streptomyces setonii MCs formed a subfamily, clearly distinguished from those of other MCs.