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Publications - Cell and Metabolic Biology

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Publications

Bilova, T.; Paudel, G.; Shilyaev, N.; Schmidt, R.; Brauch, D.; Tarakhovskaya, E.; Milrud, S.; Smolikova, G.; Tissier, A.; Vogt, T.; Sinz, A.; Brandt, W.; Birkemeyer, C.; Wessjohann, L. A.; Frolov, A.; Global proteomic analysis of advanced glycation end products in the Arabidopsis proteome provides evidence for age-related glycation hot spots J. Biol. Chem. 292, 15758-15776, (2017) DOI: 10.1074/jbc.M117.794537

Glycation is a post-translational modification resulting from the interaction of protein amino and guanidino groups with carbonyl compounds. Initially, amino groups react with reducing carbohydrates, yielding Amadori and Heyns compounds. Their further degradation results in formation of advanced glycation end products (AGEs), also originating from α-dicarbonyl products of monosaccharide autoxidation and primary metabolism. In mammals, AGEs are continuously formed during the life of the organism, accumulate in tissues, are well-known markers of aging, and impact age-related tissue stiffening and atherosclerotic changes. However, the role of AGEs in age-related molecular alterations in plants is still unknown. To fill this gap, we present here a comprehensive study of the age-related changes in the Arabidopsis thaliana glycated proteome, including the proteins affected and specific glycation sites therein. We also consider the qualitative and quantitative changes in glycation patterns in terms of the general metabolic background, pathways of AGE formation, and the status of plant anti-oxidative/anti-glycative defense. Although the patterns of glycated proteins were only minimally influenced by plant age, the abundance of 96 AGE sites in 71 proteins was significantly affected in an age-dependent manner and clearly indicated the existence of age-related glycation hot spots in the plant proteome. Homology modeling revealed glutamyl and aspartyl residues in close proximity (less than 5 Å) to these sites in three aging-specific and eight differentially glycated proteins, four of which were modified in catalytic domains. Thus, the sites of glycation hot spots might be defined by protein structure that indicates, at least partly, site-specific character of glycation.
Publications

Bilova, T.; Lukasheva, E.; Brauch, D.; Greifenhagen, U.; Paudel, G.; Tarakhovskaya, E.; Frolova, N.; Mittasch, J.; Balcke, G. U.; Tissier, A.; Osmolovskaya, N.; Vogt, T.; Wessjohann, L. A.; Birkemeyer, C.; Milkowski, C.; Frolov, A.; A Snapshot of the Plant Glycated Proteome: STRUCTURAL, FUNCTIONAL, AND MECHANISTIC ASPECTS J. Biol. Chem. 291, 7621-7636, (2016) DOI: 10.1074/jbc.M115.678581

Glycation is the reaction of carbonyl compounds (reducing sugars and α-dicarbonyls) with amino acids, lipids, and proteins, yielding early and advanced glycation end products (AGEs). The AGEs can be formed via degradation of early glycation intermediates (glycoxidation) and by interaction with the products of monosaccharide autoxidation (autoxidative glycosylation). Although formation of these potentially deleterious compounds is well characterized in animal systems and thermally treated foods, only a little information about advanced glycation in plants is available. Thus, the knowledge of the plant AGE patterns and the underlying pathways of their formation are completely missing. To fill this gap, we describe the AGE-modified proteome of Brassica napus and characterize individual sites of advanced glycation by the methods of liquid chromatography-based bottom-up proteomics. The modification patterns were complex but reproducible: 789 AGE-modified peptides in 772 proteins were detected in two independent experiments. In contrast, only 168 polypeptides contained early glycated lysines, which did not resemble the sites of advanced glycation. Similar observations were made with Arabidopsis thaliana. The absence of the early glycated precursors of the AGE-modified protein residues indicated autoxidative glycosylation, but not glycoxidation, as the major pathway of AGE formation. To prove this assumption and to identify the potential modifying agents, we estimated the reactivity and glycative potential of plant-derived sugars using a model peptide approach and liquid chromatography-mass spectrometry-based techniques. Evaluation of these data sets together with the assessed tissue carbohydrate contents revealed dihydroxyacetone phosphate, glyceraldehyde 3-phosphate, ribulose, erythrose, and sucrose as potential precursors of plant AGEs.
Publications

Teutschbein, J.; Gross, W.; Nimtz, M.; Milkowski, C.; Hause, B.; Strack, D.; Identification and Localization of a Lipase-like Acyltransferase in Phenylpropanoid Metabolism of Tomato (Solanum lycopersicum) J. Biol. Chem. 285, 38374-38381, (2010) DOI: 10.1074/jbc.M110.171637

We have isolated an enzyme classified as chlorogenate: glucarate caffeoyltransferase (CGT) from seedlings of tomato (Solanum lycopersicum) that catalyzes the formation of caffeoylglucarate and caffeoylgalactarate using chlorogenate (5-O-caffeoylquinate) as acyl donor. Peptide sequences obtained by trypsin digestion and spectrometric sequencing were used to isolate the SlCGT cDNA encoding a protein of 380 amino acids with a putative targeting signal of 24 amino acids indicating an entry of the SlCGT into the secretory pathway. Immunogold electron microscopy revealed the localization of the enzyme in the apoplastic space of tomato leaves. Southern blot analysis of genomic cDNA suggests that SlCGT is encoded by a single-copy gene. The SlCGT cDNA was functionally expressed in Nicotiana benthamiana leaves and proved to confer chlorogenate-dependent caffeoyltransferase activity in the presence of glucarate. Sequence comparison of the deduced amino acid sequence identified the protein unexpectedly as a GDSL lipase-like protein, representing a new member of the SGNH protein superfamily. Lipases of this family employ a catalytic triad of Ser-Asp-His with Ser as nucleophile of the GDSL motif. Site-directed mutagenesis of each residue of the assumed respective SlCGT catalytic triad, however, indicated that the catalytic triad of the GDSL lipase is not essential for SlCGT enzymatic activity. SlCGT is therefore the first example of a GDSL lipase-like protein that lost hydrolytic activity and has acquired a completely new function in plant metabolism, functioning in secondary metabolism as acyltransferase in synthesis of hydroxycinnamate esters by employing amino acid residues different from the lipase catalytic triad.
Publications

Kopycki, J. G.; Stubbs, M. T.; Brandt, W.; Hagemann, M.; Porzel, A.; Schmidt, J.; Schliemann, W.; Zenk, M. H.; Vogt, T.; Functional and Structural Characterization of a Cation-dependent O-Methyltransferase from the Cyanobacterium Synechocystis sp. Strain PCC 6803 J. Biol. Chem. 283, 20888-20896, (2008) DOI: 10.1074/jbc.M801943200

The coding sequence of the cyanobacterium Synechocystis sp. strain PCC 6803 slr0095 gene was cloned and functionally expressed in Escherichia coli. The corresponding enzyme was classified as a cation- and S-adenosyl-l-methionine-dependent O-methyltransferase (SynOMT), consistent with considerable amino acid sequence identities to eukaryotic O-methyltransferases (OMTs). The substrate specificity of SynOMT was similar with those of plant and mammalian CCoAOMT-like proteins accepting a variety of hydroxycinnamic acids and flavonoids as substrates. In contrast to the known mammalian and plant enzymes, which exclusively methylate the meta-hydroxyl position of aromatic di- and trihydroxy systems, Syn-OMT also methylates the para-position of hydroxycinnamic acids like 5-hydroxyferulic and 3,4,5-trihydroxycinnamic acid, resulting in the formation of novel compounds. The x-ray structure of SynOMT indicates that the active site allows for two alternative orientations of the hydroxylated substrates in comparison to the active sites of animal and plant enzymes, consistent with the observed preferred para-methylation and position promiscuity. Lys3 close to the N terminus of the recombinant protein appears to play a key role in the activity of the enzyme. The possible implications of these results with respect to modifications of precursors of polymers like lignin are discussed.
Publications

Ibdah, M.; Zhang, X.-H.; Schmidt, J.; Vogt, T.; A Novel Mg2+-dependent O-Methyltransferase in the Phenylpropanoid Metabolism of Mesembryanthemum crystallinum J. Biol. Chem. 278, 43961-43972, (2003) DOI: 10.1074/jbc.M304932200

Upon irradiation with elevated light intensities, the ice plant (Mesembryanthemum crystallinum) accumulates a complex pattern of methylated and glycosylated flavonol conjugates in the upper epidermal layer. Identification of a flavonol methylating activity, partial purification of the enzyme, and sequencing of the corresponding peptide fragments revealed a novel S-adenosyl-l-methionine-dependent O-methyltransferase that was specific for flavonoids and caffeoyl-CoA. Cloning and functional expression of the corresponding cDNA verified that the new methyltransferase is a multifunctional 26.6-kDa Mg2+-dependent enzyme, which shows a significant sequence similarity to the cluster of caffeoyl coenzyme A-methylating enzymes. Functional analysis of highly homologous members from chickweed (Stellaria longipes), Arabidopsis thaliana, and tobacco (Nicotiana tabacum) demonstrated that the enzymes from the ice plant, chickweed, and A. thaliana possess a broader substrate specificity toward o-hydroquinone-like structures than previously anticipated for Mg2+-dependent O-methyltransferases, and are distinctly different from the tobacco enzyme. Besides caffeoyl-CoA and flavonols, a high specificity was also observed for caffeoylglucose, a compound never before reported to be methylated by any plant O-methyltransferase. Based on phylogenetic analysis of the amino acid sequence and differences in acceptor specificities among both animal and plant O-methyltransferases, we propose that the enzymes from the Centrospermae, along with the predicted gene product from A. thaliana, form a novel subclass within the caffeoyl coenzyme A-dependent O-methyltransferases, with potential divergent functions not restricted to lignin monomer biosynthesis.
Publications

Ziegler, J.; Stenzel, I.; Hause, B.; Maucher, H.; Hamberg, M.; Grimm, R.; Ganal, M.; Wasternack, C.; Molecular Cloning of Allene Oxide Cyclase J. Biol. Chem. 275, 19132-19138, (2000) DOI: 10.1074/jbc.M002133200

Allene oxide cyclase (EC 5.3.99.6) catalyzes the stereospecific cyclization of an unstable allene oxide to (9S,13S)-12-oxo-(10,15Z)-phytodienoic acid, the ultimate precursor of jasmonic acid. This dimeric enzyme has previously been purified, and two almost identical N-terminal peptides were found, suggesting allene oxide cyclase to be a homodimeric protein. Furthermore, the native protein was N-terminally processed. Using degenerate primers, a polymerase chain reaction fragment could be generated from tomato, which was further used to isolate a full-length cDNA clone of 1 kilobase pair coding for a protein of 245 amino acids with a molecular mass of 26 kDa. Whereas expression of the whole coding region failed to detect allene oxide cyclase activity, a 5′-truncated protein showed high activity, suggesting that additional amino acids impair the enzymatic function. Steric analysis of the 12-oxophytodienoic acid formed by the recombinant enzyme revealed exclusive (>99%) formation of the 9S,13Senantiomer. Exclusive formation of this enantiomer was also found in wounded tomato leaves. Southern analysis and genetic mapping revealed the existence of a single gene for allene oxide cyclase located on chromosome 2 of tomato. Inspection of the N terminus revealed the presence of a chloroplastic transit peptide, and the location of allene oxide cyclase protein in that compartment could be shown by immunohistochemical methods. Concomitant with the jasmonate levels, the accumulation of allene oxide cyclase mRNA was transiently induced after wounding of tomato leaves.
Publications

Schmidt, A.; Grimm, R.; Schmidt, J.; Scheel, D.; Strack, D.; Rosahl, S.; Cloning and Expression of a Potato cDNA Encoding Hydroxycinnamoyl-CoA:Tyramine N-(Hydroxycinnamoyl)transferase J. Biol. Chem. 274, 4273-4280, (1999) DOI: 10.1074/jbc.274.7.4273

Hydroxycinnamoyl-CoA:tyramineN-(hydroxycinnamoyl)transferase (THT; EC 2.3.1.110) catalyzes the transfer of hydroxycinnamic acids from the respective CoA esters to tyramine and other amines in the formation ofN-(hydroxycinnamoyl)amines. Expression of THT is induced byPhytophthora infestans, the causative agent of late blight disease in potato. The amino acid sequences of nine endopeptidase LysC-liberated peptides from purified potato THT were determined. Using degenerate primers, a THT-specific fragment was obtained by reverse transcription-polymerase chain reaction, and THT cDNA clones were isolated from a library constructed from RNA of elicitor-treated potato cells. The open reading frame encoding a protein of 248 amino acids was expressed in Escherichia coli. Recombinant THT exhibited a broad substrate specificity, similar to that of native potato THT, accepting cinnamoyl-, 4-coumaroyl-, caffeoyl-, feruloyl- and sinapoyl-CoA as acyl donors and tyramine, octopamine, and noradrenalin as acceptors tested. Elicitor-induced THT transcript accumulation in cultured potato cells peaked 5 h after initiation of treatment, whereas enzyme activity was highest from 5 to 30 h after elicitation. In soil-grown potato plants, THT mRNA was most abundant in roots. Genomic Southern analyses indicate that, in potato, THT is encoded by a multigene family.
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