Postimport methylation of the small subunit of ribulose-1,5-bisphosphate carboxylase in chloroplasts

• Published in: FEBS letters 1997-05, Vol.408 (3), p.350-354
• Main Authors: Grimm, Rudolf, Grimm, Monika, Eckerskorn, Christoph, Pohlmeyer, Kai, Röhl, Thomas, Soll, Jürgen
• Format: Article
• Language: English
• Subjects: Chloroplasts - enzymology; Chromatography, High Pressure Liquid; diphenylthiourea; DPTU; EI-MS; electron impact mass spectronomy; high performance liquid chromatography; Hordeum - metabolism; HPLC; Kinetics; large subunit of Rubisco; LSU; Macromolecular Substances; MALDI-TOF/MS; Mass Spectrometry - methods; matrix assisted laser desorption ionization-time of flight mass sprectronomy; Methylation; Methyltransferases - metabolism; Peptide Fragments - chemistry; Peptide Fragments - isolation & purification; phenylthiohydantoin; Pisum sativum - metabolism; Pisum sativum L; Post-translational modification; precursor form of SSU; preSSU; Protein import; Protein methyl transferase; PTH; ribulose-1,5-bisphosphate carboxylase; Ribulose-Bisphosphate Carboxylase - chemistry; Ribulose-Bisphosphate Carboxylase - isolation & purification; Ribulose-Bisphosphate Carboxylase - metabolism; Rubisco; S-adenosylmethionine; SAM; small subunit of Rubisco; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - methods; Spinacia oleracea - metabolism; SSU; Thiourea - analogs & derivatives; Zea mays - metabolism
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/S0014-5793(97)00462-6

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.