Functional analysis of aromatic biosynthetic pathways in Pseudomonas putida KT2440.
Bottom Line: Genes for tryptophan biosynthesis are grouped in unlinked regions with the trpBA and trpGDE genes organized as operons and the trpI, trpE and trpF genes organized as single transcriptional units.The pheA and tyrA gene-encoding multifunctional enzymes for phenylalanine and tyrosine biosynthesis are linked in the chromosome and form an operon with the serC gene involved in serine biosynthesis.The last step in the biosynthesis of these two amino acids requires an amino transferase activity for which multiple tyrB-like genes are present in the host chromosome.
Affiliation: Consejo Superior de Investigaciones Científicas, Estación del Zaidín, Department of Environmental Protection, Granada, Spain.Show MeSH
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Mentions: Pseudomonas putida KT2440 can grow on minimal medium and should therefore contain all the necessary genetic information for the biosynthesis of all proteinogenic amino acids. However, no detailed global functional study has ever been undertaken regarding the biosynthesis of amino acids in this strain, and few studies have dealt with this issue in other strains of the genus Pseudomonas (Isaac and Holloway, 1968; Calhoun and Weary, 1969;Buvinger et al., 1981; Cuppels 1986; Essar et al., 1990a,b; Lindow et al., 1993). The number of auxotrophs described for P. putida mt‐2 and its derivatives is restricted to a tryptophan auxotroph of P. putida mt‐2 (Worsey and Williams, 1975). Although few mutants requiring aromatic amino acids have been isolated, information regarding the biochemical biosynthesis of these amino acids has received considerable attention (Gussin, 2004). As in other eubacteria, the biosynthesis of aromatic amino acids in Pseudomonas starts with chorismate as the ultimate intermediate (Fig. 1), which can be transformed into either anthranilate, by the action of anthranilate synthase (TrpE/TrpG), or prephenate by one of the activities associated to the pheA gene product. The biosynthesis of tryptophan from anthranilate follows a one‐way pathway (Fig. 2) (Gussin, 2004), whereas the biosynthesis of tyrosine and phenylalanine is achieved through branched pathways in which one of the most surprising findings is that the pheA gene product participates in multiple steps (Berry, 1996 and Fig. 1). In this branched pathway TyrA is also a multifunctional enzyme and a number of TyrB aminotransferases are involved in the biosynthesis of phenylalanine and tyrosine from phenylpyruvate and 4‐hydroxyphenylpyruvate respectively (Whitaker et al., 1982). Ultimately, l‐tyrosine is also made from l‐phenylalanine in a reaction catalysed by PhhA (Zhao et al., 1994; Arias‐Barrau et al., 2004; Herrera and Ramos, 2007).
Affiliation: Consejo Superior de Investigaciones Científicas, Estación del Zaidín, Department of Environmental Protection, Granada, Spain.