title: Pyridine nucleotide transhydrogenase PntAB is essential for optimal growth and photosynthetic integrity under low-light mixotrophic conditions in Synechocystis sp. PCC 6803.
abstract: Pyridine nucleotide transhydrogenase (PntAB) is an integral membrane protein complex participating in the regulation of NAD(P)+:NAD(P)H redox homeostasis in various prokaryotic and eukaryotic organisms. In the present study we addressed the function and biological role of PntAB in oxygenic photosynthetic cyanobacteria capable of both autotrophic and heterotrophic growth, with support from structural three-dimensional (3D)-modeling. The pntA gene encoding the α subunit of heteromultimeric PntAB in Synechocystis sp. PCC 6803 was inactivated, followed by phenotypic and biophysical characterization of the ΔpntA mutant under autotrophic and mixotrophic conditions. Disruption of pntA resulted in phenotypic growth defects observed under low light intensities in the presence of glucose, whereas under autotrophic conditions the mutant did not differ from the wild-type strain. Biophysical characterization and protein-level analysis of the ΔpntA mutant revealed that the phenotypic defects were accompanied by significant malfunction and damage of the photosynthetic machinery. Our observations link the activity of PntAB in Synechocystis directly to mixotrophic growth, implicating that under these conditions PntAB functions to balance the NADH: NADPH equilibrium specifically in the direction of NADPH. The results also emphasize the importance of NAD(P)+:NAD(P)H redox homeostasis and associated ATP:ADP equilibrium for maintaining the integrity of the photosynthetic apparatus under low-light glycolytic metabolism.
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014, Turun Yliopisto, Finland.
authors.forename: Jari
authors.initials: J
authors.lastname: Kämäräinen
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014, Turun Yliopisto, Finland.
authors.forename: Tuomas
authors.initials: T
authors.lastname: Huokko
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014, Turun Yliopisto, Finland.
authors.forename: Sanna
authors.initials: S
authors.lastname: Kreula
authors.affiliation: Department of Life Sciences, Imperial College London, Sir Alexander Fleming Building, London, SW7 2AZ, UK.
authors.forename: Patrik R
authors.initials: PR
authors.lastname: Jones
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014, Turun Yliopisto, Finland.
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014, Turun Yliopisto, Finland.
authors.forename: Pauli
authors.initials: P
authors.lastname: Kallio
mesh_terms: D052818:Autotrophic Processes; D001426:Bacterial Proteins / Q000378:metabolism; D017353:Gene Deletion; D005947:Glucose / Q000494:pharmacology; D008027:Light; D008958:Models, Molecular; D009250:NADP Transhydrogenases / Q000378:metabolism*; D010641:Phenotype; D010788:Photosynthesis / Q000528:radiation effects*; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013050:Spectrometry, Fluorescence; D046939:Synechocystis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects; D020524:Thylakoids / Q000201:enzymology
chemical_list: D001426:Bacterial Proteins; D009250:NADP Transhydrogenases; D005947:Glucose
keywords: NAD(P)H; PntAB; Transhydrogenase; cyanobacteria; low-light; mixotrophic; photobioreactor MC1000; photosynthetic machinery