Glyceraldehyde‐3‐phosphate dehydrogenase is regulated by ferredoxin‐NADP reductase in the diatom Asterionella formosa

Abstract

SummaryDiatoms are a widespread and ecologically important group of heterokont algae that contribute c. 20% to global productivity. Previous work has shown that regulation of their key Calvin cycle enzymes differs from that of the Plantae, and that in crude extracts, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) can be inhibited by nicotinamide adenine dinucleotide phosphate reduced (NADPH) under oxidizing conditions.The freshwater diatom, Asterionella formosa, was studied using enzyme kinetics, chromatography, surface plasmon resonance, mass spectrometry and sequence analysis to determine the mechanism behind this GAPDH inhibition.GAPDH interacted with ferredoxin-nicotinamide adenine dinucleotide phosphate (NADP) reductase (FNR) from the primary phase of photosynthesis, and the small chloroplast protein, CP12. Sequences of copurified GAPDH and FNR were highly homologous with published sequences. However, the widespread ternary complex among GAPDH, phosphoribulokinase and CP12 was absent. Activity measurements under oxidizing conditions showed that NADPH can inhibit GAPDH-CP12 in the presence of FNR, explaining the earlier observed inhibition within crude extracts.Diatom plastids have a distinctive metabolism, including the lack of the oxidative pentose phosphate pathway, and so cannot produce NADPH in the dark. The observed down-regulation of GAPDH in the dark may allow NADPH to be rerouted towards other reductive processes contributing to their ecological success.

The nature of the CO2‐concentrating mechanisms in a marine diatom, Thalassiosira pseudonana

“…The soluble protein extracts were prepared as described previously (Erales et al, 2008;Mekhalfi et al, 2014) in a buffer containing 1 mM NAD. The soluble protein concentration of crude extracts was assayed using the Bio-Rad (Hercules, CA, USA) reagent using BSA as a standard (Bradford, 1976).…”

Phosphoribulokinase from Chlamydomonas reinhardtii: a Benson–Calvin cycle enzyme enslaved to its cysteine residues

“…PCC 7942 possesses the two regulatory cysteine residues and is redox regulated like the eukaryotic PRKs although they are separated by only 22 amino acids. 26 PRK and CP12 were also shown to interact in the absence of GAPDH, 25 although their interaction is much weaker (K d in the mM range) than the GAPDH-CP12 interaction (K d in the nM range). 1).…”

Transcriptomic responses to thermal stress and varied phosphorus conditions in Symbiodinium kawagutii

“…Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and glycerol-3-phosphate dehydrogenase (GPDH) genes were greatly up-regulated. GAPDH interacts with different biomolecules, and has been known to play an important role in diatom’s ecological success (109). In Chironomidae, GAPDH enhances heavy metal tolerance by adaptive molecular changes through binding at the active site (110).…”