The intriguing CP12-like tail of adenylate kinase 3 from Chlamydomonas reinhardtii

Adenylate kinases (ADK) are key enzymes that maintain the energetic balance in cellular compartments by catalyzing the reaction: AMP + ATP2 ADP. Here, we analyzed the chloroplast ADK 3 from the green alga, Chlamydomonas reinhardtii for the first time. This enzyme bears a C-terminal extension that is highly similar to the C-terminal end of the intrinsically disordered protein CP12 that plays a major role in the redox regulation of key enzymes of the Calvin-Benson cycle like glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and phosphoribulokinase. The only other known example of a CP12-like extension is found in the GapB isoform of GAPDH, where it is responsible for the autonomous redox regulation of the higher plant A(2)B(2) GAPDH. In this study, we show that the CP12-like tail is not involved in the redox regulation of ADK 3, but contributes greatly to its stability, and is essential for the post-translational modification of the Cys221 residue by glutathione. This report highlights the fact that the C-terminal part of the CP12 protein can act as a moonlighting, intrinsically disordered module conferring additional capabilities to the proteins to which it is added. EnzymesAdenylate kinase (ADK, ) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH, )