Cloning of the genes for a 4-sulphocatechol-oxidizing protocatechuate 3,4-dioxygenase from Hydrogenophaga intermedia S1 and identification of the amino acid residues responsible for the ability to convert 4-sulphocatechol.

The genes for a protocatechuate 3,4-dioxygenase (P34O-II) with the ability to oxidize 4-sulphocatechol were cloned from the 4-aminobenzenesulphonate(sulphanilate)-degrading bacterium Hydrogenophaga intermedia strain S1 (DSMZ 5680). Sequence comparisons of the deduced amino acid sequences of both subunits of the P34O-II from H. intermedia S1 (PcaH-II and PcaG-II) with those of another P34O-II, previously obtained from Agrobacterium radiobacter S2, and the corresponding sequences from the protocatechuate 3,4-dioxygenases from other bacterial genera demonstrated that seven amino acid residues, which were conserved in all previously known P34Os (P34O-Is), were different in both P34O-IIs. According to previously published structural data for the P34O of Pseudomonas putida only two of these amino acid residues were located near the catalytical centre. The respective amino acid residues were mutated in the P34O-I from A. radiobacter S2 by site-specific mutagenesis, and it was found that a single amino acid exchange enabled the protocatechuate converting P34O also to oxidize 4-sulphocatechol.