Pseudomonas aeruginosa PAO1 genes for 3-guanidinopropionate and 4-guanidinobutyrate utilization may be derived from a common ancestor

摘要

Pseudomonas aeruginosa PAO1 utilizes 3-guanidinopropionate (3-GP) and 4-guanidinobutyrate (4-GB), which differ in one methylene group only, via distinct enzymes: guanidinopropionase (EC 3.5.3.17; the gpuA product) and guanidinobutyrase (EC 3.5.3.7; the gbuA product). The authors cloned and characterized the contiguous gpuPAR genes (in that order) responsible for 3-GP utilization, and compared the deduced sequences of their putative protein products, and the potential regulatory mechanisms of gpuPA, with those of the corresponding gbu genes encoding the 4-GB catabolic system. GpuA and GpuR have similarity to GbuA (49?% identity) and GbuR (a transcription activator of gbuA; 37?% identity), respectively. GpuP resembles PA1418 (58?% identity), which is a putative membrane protein encoded by a potential gene downstream of gbuA. These features of the GpuR and GpuP sequences, and the impaired growth of gpuR and gpuP knockout mutants on 3-GP, support the notion that GpuR and GpuP direct the 3-GP-inducible expression of gpuA, and the uptake of 3-GP, respectively. Northern blots of mRNA from 3-GP-induced PAO1 cells revealed three transcripts of gpuA, gpuP, and gpuP and gpuA together, suggesting that gpuP and gpuA each have a 3-GP-responsible promoter, and that some transcription from the gpuP promoter is terminated after gpuP, or proceeds into gpuA. Knockout of gpuR abolished 3-GP-dependent synthesis of the transcripts, confirming that GpuR activates transcription from these promoters, with 3-GP as a specific co-inducer. The sequence conservation between the three functional pairs of the Gpu and Gbu proteins, and the absence of gpuAPR in closely related species, imply that the triad gpu genes have co-ordinately evolved from origins common to the gbu counterparts, to establish an independent catabolic system of 3-GP in P. aeruginosa.