Functional correlation of dibenzothiophene and benzothiophene desulfurization enzymes

Gordonia sp. C-6 can desulfurize benzothiophene (BT) as the pathway similar to the "4S" pathway of dibenzothiophene (DBT)-desulfurizing, but the strain can not grow with DBT as the sole sulfur source. At current, there were not related reports on BT-desulfurizing genes at home or abroad. The DBT-desulfurizing genes of Rhodocossus erythropolis DS-3, dszA, dszB, dszC and dszABC were introduced into Gordonia sp. C-6 respectively using a Rhodococcus-E. coli shuttle vector, to construct new recombinant strains Gordonia sp. CRA, Gordonia sp. CRB, Gordonia sp. CRC and Gordonia sp. CRABC, the enzyme activities of which was respectively 76.8 micromol x (g x h)(-1), 51.6 micromol x (g x h)(-1) and 62.4 micromol x (g x h)(-1), increasing by 1.5 times compared with 35.2 micromol x (g x h)(-1), 21.3 micromol x (g x h)(-1) and 25.5 micromol x (g x h)(-1) of wild strain Rhodocossus erythropolis DS-3. Of the recombinant strains, only recombinant strains Gordonia sp. CRC with DszC and Gordonia sp. CRABC with DszABC exhibite significant growth with DBT as the sole sulfur source, Gordonia sp. CRA with DszA and Gordonia sp. CRB with DszB could not live with DBT as the sole sulfur source. The results show that, DBT monoxygenase and BT monoxygenase, catalyzed the first two steps of DBT and BT oxidation, respectively, are the key enzymes responsible for substrate-recognition, however, the enzymes catalyzed the last two steps have the similar substrate specificity. The active sites of the two monoxygenase could be predicted by comparing with the sequence differences of their amino acids.