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

Abstract

Pseudomonas aeruginosaPAO1 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; thegpuAproduct) and guanidinobutyrase (EC 3.5.3.7; thegbuAproduct). The authors cloned and characterized the contiguousgpuPARgenes (in that order) responsible for 3-GP utilization, and compared the deduced sequences of their putative protein products, and the potential regulatory mechanisms ofgpuPA, with those of the correspondinggbugenes encoding the 4-GB catabolic system. GpuA and GpuR have similarity to GbuA (49 % identity) and GbuR (a transcription activator ofgbuA; 37 % identity), respectively. GpuP resembles PA1418 (58 % identity), which is a putative membrane protein encoded by a potential gene downstream ofgbuA. These features of the GpuR and GpuP sequences, and the impaired growth ofgpuRandgpuPknockout mutants on 3-GP, support the notion that GpuR and GpuP direct the 3-GP-inducible expression ofgpuA, and the uptake of 3-GP, respectively. Northern blots of mRNA from 3-GP-induced PAO1 cells revealed three transcripts ofgpuA,gpuP, andgpuPandgpuAtogether, suggesting thatgpuPandgpuAeach have a 3-GP-responsible promoter, and that some transcription from thegpuPpromoter is terminated aftergpuP, or proceeds intogpuA. Knockout ofgpuRabolished 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 ofgpuAPRin closely related species, imply that the triadgpugenes have co-ordinately evolved from origins common to thegbucounterparts, to establish an independent catabolic system of 3-GP inP. aeruginosa.