The periplasmic transaminase PtaA of Pseudomonas fluorescens converts the glutamic acid residue at the pyoverdine fluorophore to α-ketoglutaric acid
- authored by
- Michael T. Ringel, Gerald Dräger, Thomas Brüser
- Abstract
The periplasmic conversion of ferribactin to pyoverdine is essential for siderophore biogenesis in fluorescent pseudomonads, such as pathogenic Pseudomonas aeruginosa or plant growth-promoting Pseudomonas fluorescens. The non-ribo-somal peptide ferribactin undergoes cyclizations and oxidations that result in the fluorophore, and a strictly conserved fluorophore-bound glutamic acid residue is converted to a range of variants, including succinamide, succinic acid, and -ketoglu-taric acid residues. We recently discovered that the pyridoxal phosphate-containing enzyme PvdN is responsible for the generation of the succinamide, which can be hydrolyzed to succinic acid. Based on this, a distinct unknown enzyme was postulated to be responsible for the conversion of the glutamic acid to -ke-toglutaric acid. Here we report the identification and characterization of this enzyme in P. fluorescens strain A506. In silico analyses indicated a periplasmic transaminase in fluorescent pseudomonads and other proteobacteria that we termed PtaA for “periplasmic transaminase A.” An in-frame-deleted ptaA mutant selectively lacked the -ketoglutaric acid form of pyoverdine, and recombinant PtaA complemented this phenotype. The ptaA/pvdN double mutant produced exclusively the glutamic acid form of pyoverdine. PtaA is homodimeric and contains a pyridoxal phosphate cofactor. Mutation of the active-site lysine abolished PtaA activity and affected folding as well as Tat-dependent transport of the enzyme. In pseudomonads, the occurrence of ptaA correlates with the occurrence of -ke-toglutaric acid forms of pyoverdines. As this enzyme is not restricted to pyoverdine-producing bacteria, its catalysis of periplasmic transaminations is most likely a general tool for specific biosynthetic pathways.
- Organisation(s)
-
Institute of Microbiology
Institute of Organic Chemistry
- Type
- Article
- Journal
- Journal of Biological Chemistry
- Volume
- 292
- Pages
- 18660-18671
- No. of pages
- 12
- ISSN
- 0021-9258
- Publication date
- 10.11.2017
- Publication status
- Published
- Peer reviewed
- Yes
- ASJC Scopus subject areas
- Biochemistry, Molecular Biology, Cell Biology
- Electronic version(s)
-
https://doi.org/10.1074/jbc.M117.812545 (Access:
Open)