title: Exploring CP12 binding proteins revealed aldolase as a new partner for the phosphoribulokinase/glyceraldehyde 3-phosphate dehydrogenase/CP12 complex--purification and kinetic characterization of this enzyme from Chlamydomonas reinhardtii.
abstract: Possible binding proteins of CP12 in a green alga, Chlamydomonas reinhardtii, were investigated. We covalently immobilized CP12 on a resin and then used it to trap CP12 partners. Thus, we found an association between CP12 and phosphoribulokinase (EC 2.7.1.19), glyceraldehyde 3-phosphate dehydrogenase (EC 1.2.1.13) and aldolase. Immunoprecipitation with purified CP12 antibodies supported these data. The dissociation constant between CP12 and fructose 1,6-bisphosphate (EC 4.1.2.13) aldolase was measured by surface plasmon resonance and is equal to 0.48 +/- 0.05 mum and thus corroborated an interaction between CP12 and aldolase. However, the association is even stronger between aldolase and the phosphoribulokinase/glyceraldehyde 3-phosphate dehydrogenase/CP12 complex and the dissociation constant between them is equal to 55+/-5 nm. Moreover, owing to the fact that aldolase has been poorly studied in C. reinhardtii, we purified it and analyzed its kinetic properties. The enzyme displayed Michaelis-Menten kinetics with fructose 1,6-bisphosphate and sedoheptulose 1,7-bisphosphate, with a catalytic constant equal to 35 +/- 1 s(-1) and 4 +/- 0.1 s(-1), respectively. The K(m) value for fructose 1,6-bisphosphate was equal to 0.16 +/- 0.02 mm and 0.046 +/- 0.005 mm for sedoheptulose 1,7-bisphosphate. The catalytic efficiency of aldolase was thus 219 +/- 31 s(-1).mm(-1) with fructose 1,6-bisphosphate and 87 +/- 9 s(-1).mm(-1) with sedoheptulose 1,7-bisphosphate. In the presence of the complex, this parameter for fructose 1,6-bisphosphate increased to 310 +/- 23 s(-1).mm(-1), whereas no change was observed with sedoheptulose 1,7-bisphosphate. The condensation reaction of aldolase to form fructose 1,6-bisphosphate was also investigated but no effect of CP12 or the complex on this reaction was observed.
authors.affiliation: Laboratoire d'Enzymologie de Complexes Supramoléculaires, UPR 90 36, BIP-Centre National de la Recherche Scientifique, 31 Chemin J. Aiguier, Marseille Cedex 20, France.
authors.forename: Jenny
authors.initials: J
authors.lastname: Erales
authors.forename: Luisana
authors.initials: L
authors.lastname: Avilan
authors.forename: Sandrine
authors.initials: S
authors.lastname: Lebreton
authors.forename: Brigitte
authors.initials: B
authors.lastname: Gontero
mesh_terms: D020418:Algal Proteins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000201:enzymology*; D005634:Fructose-Bisphosphate Aldolase / Q000737:chemistry / Q000378:metabolism*; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000737:chemistry / Q000378:metabolism*; D047468:Immunoprecipitation; D007700:Kinetics; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D020418:Algal Proteins; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D017853:Phosphotransferases (Alcohol Group Acceptor); C022390:phosphoribulokinase; D005634:Fructose-Bisphosphate Aldolase