title: Postimport methylation of the small subunit of ribulose-1,5-bisphosphate carboxylase in chloroplasts.
abstract: Electron impact mass spectronomy analysis of the amino-terminal amino acid of the small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase (Rubisco) showed that the amino-terminal methionine residue is post-translationally modified to N-methyl-methionine. Modification of the amino-terminal methionine residue was found in mature SSU proteins from the dicotyledonous plants pea and spinach as well as the monocotyledonous plants barley and corn. SSU methyltransferase is a soluble protein in the chloroplast stroma and accepts heterologously expressed non-methylated SSU as a substrate using S-adenosylmethionine as methyl-group donor. We show that this modification occurs after post-translational uptake of the precursor form of SSU into chloroplasts and processing to its mature size. This reaction represents a new step in the import and assembly pathway of Rubisco holoenzyme.
authors.affiliation: Hewlett-Packard Chemical Analysis Group Europe, Waldbronn, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Grimm
authors.forename: M
authors.initials: M
authors.lastname: Grimm
authors.forename: C
authors.initials: C
authors.lastname: Eckerskorn
authors.forename: K
authors.initials: K
authors.lastname: Pohlmeyer
authors.forename: T
authors.initials: T
authors.lastname: Röhl
authors.forename: J
authors.initials: J
authors.lastname: Soll
mesh_terms: D002736:Chloroplasts / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D001467:Hordeum / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D013058:Mass Spectrometry / Q000379:methods; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D018532:Pisum sativum / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D012273:Ribulose-Bisphosphate Carboxylase / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods; D018724:Spinacia oleracea / Q000378:metabolism; D013890:Thiourea / Q000031:analogs & derivatives; D003313:Zea mays / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D010446:Peptide Fragments; C032788:diphenylthiourea; D008780:Methyltransferases; D012273:Ribulose-Bisphosphate Carboxylase; D013890:Thiourea