Characterization of Chloroplastic Fructose 1,6-Bisphosphate Aldolases as Lysine-methylated Proteins in Plants.

Morgane Mininno (1) , Sabine Brugiere (2) , Virginie Pautre (1) , Annabelle Gilgen (1) , Sheng Ma (1) , Myriam Ferro (2, 3) , Marianne Tardif (2, 3) , Claude Alban (1) , Stephane Ravanel (1)

1 LPCV - Laboratoire de physiologie cellulaire végétale
2 BGE - UMR S1038 - Laboratoire de Biologie à Grande Échelle
3 LEDyP - Laboratoire d'étude de la dynamique des protéomes

In pea (Pisum sativum), the protein-lysine methyltransferase (PsLSMT) catalyzes the trimethylation of Lys-14 in the large subunit (LS) of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), the enzyme catalyzing the CO(2) fixation step during photosynthesis. Homologs of PsLSMT, herein referred to as LSMT-like enzymes, are found in all plant genomes, but methylation of LS Rubisco is not universal in the plant kingdom, suggesting a species-specific protein substrate specificity of the methyltransferase. In this study, we report the biochemical characterization of the LSMT-like enzyme from Arabidopsis thaliana (AtLSMT-L), with a focus on its substrate specificity. We show that, in Arabidopsis, LS Rubisco is not naturally methylated and that the physiological substrates of AtLSMT-L are chloroplastic fructose 1,6-bisphosphate aldolase isoforms. These enzymes, which are involved in the assimilation of CO(2) through the Calvin cycle and in chloroplastic glycolysis, are trimethylated at a conserved lysyl residue located close to the C terminus. Both AtLSMT-L and PsLSMT are able to methylate aldolases with similar kinetic parameters and product specificity. Thus, the divergent substrate specificity of LSMT-like enzymes from pea and Arabidopsis concerns only Rubisco. AtLSMT-L is able to interact with unmethylated Rubisco, but the complex is catalytically unproductive. Trimethylation does not modify the kinetic properties and tetrameric organization of aldolases in vitro. The identification of aldolases as methyl proteins in Arabidopsis and other species like pea suggests a role of protein lysine methylation in carbon metabolism in chloroplasts.

Mots clés: plant; Arabidopsis thaliana; Pisum sativum; metabolism; chloroplast; methylation; 6-bisphophate aldolase; kinetic properties; substrate specificity; ribulose bisphosphate carboxylase; fructose 1; LSMT; protein lysine methyltransferase; enzyme

Domaines: Biochimie, Biologie Moléculaire

Morgane Mininno, Sabine Brugiere, Virginie Pautre, Annabelle Gilgen, Sheng Ma, et al.. Characterization of Chloroplastic Fructose 1,6-Bisphosphate Aldolases as Lysine-methylated Proteins in Plants.. Journal of Biological Chemistry, 2012, 287 (25), pp.21034-44. ⟨10.1074/jbc.M112.359976⟩. ⟨hal-00702116⟩