A Trajectory of Discovery: Metabolic Regulation by the Conditionally Disordered Chloroplast Protein, CP12

• Published in: Biomolecules (Basel, Switzerland) Switzerland), 2022-07, Vol.12 (8), p.1047
• Main Authors: Gérard, Cassy, Carrière, Frédéric, Receveur-Bréchot, Véronique, Launay, Hélène, Gontero, Brigitte
• Format: Article
• Language: English
• Subjects: Algae; Amino acid composition; Amino acids; Analysis; Calvin-Benson-Bassham cycle; Carbon dioxide; Cell cycle; Chloroplast Proteins - chemistry; Chloroplasts; Chloroplasts - metabolism; conditionally disordered protein; Cysteine; Cysteine - metabolism; Embryonic development; Environmental aspects; Enzymes; Genetic aspects; Glyceraldehyde-3-phosphate dehydrogenase; Glyceraldehyde-3-Phosphate Dehydrogenases - chemistry; Glyceraldehyde-3-Phosphate Dehydrogenases - metabolism; Health aspects; history of modern science; Hydrophobicity; Kinetics; Life Sciences; Mass spectrometry; Metabolic regulation; metabolism regulation; Methods; moonlighting protein; Phosphoribulokinase; Photosynthesis - physiology; Protein structure prediction; protein-protein interaction; Proteins; Redox properties; Review; Scientific imaging; Spinach
• ISSN: 2218-273X; 2218-273X
• DOI: 10.3390/biom12081047

The chloroplast protein CP12, which is widespread in photosynthetic organisms, belongs to the intrinsically disordered proteins family. This small protein (80 amino acid residues long) presents a bias in its composition; it is enriched in charged amino acids, has a small number of hydrophobic residues, and has a high proportion of disorder-promoting residues. More precisely, CP12 is a conditionally disordered proteins (CDP) dependent upon the redox state of its four cysteine residues. During the day, reducing conditions prevail in the chloroplast, and CP12 is fully disordered. Under oxidizing conditions (night), its cysteine residues form two disulfide bridges that confer some stability to some structural elements. Like many CDPs, CP12 plays key roles, and its redox-dependent conditional disorder is important for the main function of CP12: the dark/light regulation of the Calvin-Benson-Bassham (CBB) cycle responsible for CO assimilation. Oxidized CP12 binds to glyceraldehyde-3-phosphate dehydrogenase and phosphoribulokinase and thereby inhibits their activity. However, recent studies reveal that CP12 may have other functions beyond the CBB cycle regulation. In this review, we report the discovery of this protein, its features as a disordered protein, and the many functions this small protein can have.