The critical and ubiquitous enzyme adenylate kinase (ADK) catalyzes the nucleotide phosphoryl exchange reaction: 2ADP ↔ ATP + AMP. The ADK3 in the chloroplasts of the green alga Chlamydomonas reinhardtii, bears an unusual C-terminal extension that is similar to the C-terminal end of the intrinsically disordered protein CP12. In this study, we report that this enzyme, when oxidized but not when reduced, is able to interact with the chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) forming a stable complex as shown by native electrophoresis and mass spectrometry. In this bienzyme complex, the activity of ADK3 is unchanged while the NADPH-dependent activity of GAPDH is significantly inhibited. Moreover ADK3, like CP12, can protect GAPDH against thermal inactivation and aggregation. The ADK3-GAPDH bienzyme complex is unable to recruit phosphoribulokinase (PRK), in contrast with the ternary complex formed between GAPDH-CP12 and PRK. The interaction between ADK3 and GAPDH might be a mechanism to regulate the crucial ATP: NADPH ratio within chloroplasts to optimize the Calvin-Benson cycle during rapid fluctuation in environmental resources.
Enzymes: Adenylate kinase (EC 2.7.4.3), glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.13), phosphoribulokinase (PRK, EC 2.7.1.19).
Keywords: CP12; adenylate kinase; glyceraldehyde-3-phosphate dehydrogenase; phosphoribulokinase; protein-protein interaction.
© 2018 Federation of European Biochemical Societies.