TY - JOUR

T1 - The periplasmic transaminase PtaA of Pseudomonas fluorescens converts the glutamic acid residue at the pyoverdine fluorophore to α-ketoglutaric acid

AU - Ringel, Michael T.

AU - Dräger, Gerald

AU - Brüser, Thomas

N1 - Funding Information: This work was supported by the German Science Foundation (Deutsche Forschungsgemeinschaft) GRK1798 “Signaling at the Plant-Soil Interface” and Project BR 2285/7-1. The authors declare that they have no conflicts of interest with the contents of this article. This article contains supplemental Figs. S1 and S2. 1 To whom correspondence should be addressed. Tel.: 49-511-762-5945; Fax: 49-511-762-5287; E-mail: brueser@ifmb.uni-hannover.de. Publisher Copyright: © 2017 by The American Society for Biochemistry and Molecular Biology, Inc. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2017/11/10

Y1 - 2017/11/10

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85033596257&partnerID=8YFLogxK

U2 - 10.1074/jbc.M117.812545

DO - 10.1074/jbc.M117.812545

M3 - Article

C2 - 28912270

AN - SCOPUS:85033596257

VL - 292

SP - 18660

EP - 18671

JO - Journal of Biological Chemistry

JF - Journal of Biological Chemistry

SN - 0021-9258

IS - 45

ER -