Protein Methylation in Pea Chloroplasts

Abstract

The methylation of chloroplast proteins has been investigated by incubating intact pea (Pisum sativum) chloroplasts with (3H-methyl]-S-adenosylmethionine. Incubation in the light increases the amount of methylation in both the thylakoid and stromal fractions. Numerous thylakoid proteins serve as substrates for the methyltransfer reactions. Three of these thylakoid proteins are methylated to a significantly greater extent in the light than in the dark. One is a polypepfide with a molecular mass of 64 kD, a second has an Mr of 48 kD, and the third has a molecular mass of less than 10 kD. The primary stromal polypeptide methylated is the large subunit of ribulose bisphosphate carboxylase/oxygenase. One other stromal polypeptide, having a molecular mass of 24 kD, is also methylated much more in the light than in the dark. Two distinct types of protein methylation occur. One methyllinkage is stable to basic conditions whereas a second type is base labile. The base-stable linkage is indicative of N-methylation of amino acid residues while base-lability is suggestive of carboxymethylation of amino acid residues. Labeling in the light increases the percentage of methylation that is base labile in the thylakoid fraction while no difference is observed in the amount of base-labile methylations in light-labeled and dark-labeled stromal proteins. Also suggestive of carboxymethylation is the detection of volatile [3Hjmethyl radioactivity which increases during the labeling period and is greater in chloroplasts labeled in the light as opposed to being labeled in the dark; this implies in vivo tumover of the [3H]methyl group.Many types of posttranslational modifications of proteins occur in both prokaryotic and eukaryotic organisms. Examples include phosphorylation, glycosylation, and methylation.Protein methylation in prokaryotes is exemplified by Escherichia coli and Halobacterium halobium. In E. coli chemotaxis, attractant or repellent chemicals interact with cytoplasmic-membrane receptor proteins that signal to the flagella to create the desired movement ofthe bacterium either toward or away from the chemicals; then this signal is terminated by glutamate-carboxyl methylation of these receptor proteins in the case of attractants and demethylation in the case of repellents (7,14,15,22,29,31). The methylating agent is AdoMet2 (23), and the demethylation product is methanol

Engineering Triterpene and Methylated Triterpene Production in Plants Provides Biochemical and Physiological Insights into Terpene Metabolism

“…The SAM present in organelles, like the chloroplast, appears to be imported from the cytosol by specific SAM/S-adenosylhomocysteine exchange transporters that reside on the envelope membranes of plastids (Ravanel et al, 2004;Bouvier et al, 2006). The imported SAM is involved in the biogenesis of Asp-derived amino acids (Curien et al, 1998;Jander and Joshi, 2009;Sauter et al, 2013) and serves as the methyl donor for the methylation of macromolecules, such as plastid DNA (Nishiyama et al, 2002;Ahlert et al, 2009) and proteins (Houtz et al, 1989;Niemi et al, 1990;Ying et al, 1999;Trievel et al, 2003;Alban et al, 2014), and small molecule metabolites, such as prenylipids (e.g. plastoquinone, tocopherol, chlorophylls, and phylloquinone; Bouvier et al, 2005Bouvier et al, , 2006DellaPenna, 2005).…”

Posttranslational Modifications of Chloroplast Proteins: An Emerging Field

“…In addition to Rubisco and FRU-1,6-BISPHOSPHATE ALDOLASE, five additional proteins functioning in CO 2 assimilation were methylated (Alban et al, 2014). Interestingly, chloroplast protein methylation is, at least partly, induced by light (Niemi et al, 1990). Even if no functional differences between the unmethylated and trimethylated forms of the proteins studied have been described yet, it is plausible that methylation plays a regulatory or signaling role in carbon metabolism (Fig.…”

Changes in protein methylation associated with the elicitation response in cell cultures of alfalfa (Medicago sativaL.)

“…Abbreviations: SC, liquid scintillation counting; PMT, protein methyltransferase; PCMT, protein carboxyl methyltransferase; SAH, S-adenosyl-L-homocysteine; SAM, S-adenosyl-L-methionine; SDS-PAGE, SDS-polyacylamide gel electrophoresis. plants may also be inferred from the specific changes in carboxyl methylation and N-methylation which occur in peptides of the thylakoid and stroma respectively in isolated chloroplasts following illumination [8]. Protein carboxyl methyltransferase (PCMT) activities have been reported in wheat germ [9,10].…”

“…plants may also be inferred from the specific changes in carboxyl methylation and N-methylation which occur in peptides of the thylakoid and stroma respectively in isolated chloroplasts following illumination [8]. Protein carboxyl methyltransferase (PCMT) activities have been reported in wheat germ [9,10].…”