title: Characterization of chloroplastic fructose 1,6-bisphosphate aldolases as lysine-methylated proteins in plants.
abstract: 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.
authors.affiliation: INRA, USC1359, F-38054 Grenoble, France.
authors.forename: Morgane
authors.initials: M
authors.lastname: Mininno
authors.forename: Sabine
authors.initials: S
authors.lastname: Brugière
authors.forename: Virginie
authors.initials: V
authors.lastname: Pautre
authors.forename: Annabelle
authors.initials: A
authors.lastname: Gilgen
authors.forename: Sheng
authors.initials: S
authors.lastname: Ma
authors.forename: Myriam
authors.initials: M
authors.lastname: Ferro
authors.forename: Marianne
authors.initials: M
authors.lastname: Tardif
authors.forename: Claude
authors.initials: C
authors.lastname: Alban
authors.forename: Stéphane
authors.initials: S
authors.lastname: Ravanel
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D002736:Chloroplasts / Q000201:enzymology* / Q000235:genetics; D005634:Fructose-Bisphosphate Aldolase / Q000235:genetics / Q000378:metabolism*; D008745:Methylation; D018532:Pisum sativum / Q000201:enzymology* / Q000235:genetics; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism
chemical_list: D012273:Ribulose-Bisphosphate Carboxylase; D005634:Fructose-Bisphosphate Aldolase