Heterologous Expression and Characterization of the Purified Oxygenase Component of Rhodococcus globerulus P6 Biphenyl Dioxygenase and of Chimeras Derived from It

In this work, we have purified the His-tagged oxygenase (ht-oxygenase) component of Rhodococcus globerulus P6 biphenyl dioxygenase. The α or β subunit of P6 oxygenase was exchanged with the corresponding subunit of Pseudomonas sp. strain LB400 or of Comamonas testosteroni B-356 to create new chimeras that were purified ht-proteins and designated ht-α(P6)β(P6), ht-α(P6)β(LB400), ht-α(P6)β(B-356), ht-α(LB400)β(P6), and ht-α(B-356)β(P6). ht-α(P6)β(P6), ht-α(P6)β(LB400), ht-α(P6)β(B-356) were not expressed active in recombinant Escherichia coli cells carrying P6 bphA1 and bphA2, P6 bphA1 and LB400 bphE, or P6 bphA1 and B-356 bphE because the [2Fe-2S] Rieske cluster of P6 oxygenase α subunit was not assembled correctly in these clones. On the other hand ht-α(LB400)β(P6) and ht-α(B-356)β(P6) were produced active in E. coli. Furthermore, active purified ht-α(P6)β(P6), ht-α(P6)β(LB400), ht-α(P6)β(B-356), showing typical spectra for Rieske-type proteins, were obtained from Pseudomonas putida KT2440 carrying constructions derived from the new shuttle E. coli-Pseudomonas vector pEP31, designed to produce ht-proteins in Pseudomonas. Analysis of the substrate selectivity pattern of these purified chimeras toward selected chlorobiphenyls indicate that the catalytic capacity of hybrid enzymes comprised of an α and a β subunit recruited from distinct biphenyl dioxygenases is not determined specifically by either one of the two subunits.