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PubMed2005

The expression of the hydroxyproline-rich glycopeptide systemin precursor A in response to (a)biotic stress and elicitors is indicative of its role in the regulation of the wound response in tobacco (Nicotiana tabacum L.).

Two hydroxyproline-rich glycopeptide systemin (TobHS) precursor proteins known as preproTobHypSys-A and B were recently discovered in tobacco (Nicotiana tabacum L.) [Pearce et al. in Nature 411:817-820, 2001]. In this work, the effect of elicitors, insect damage, and abiotic stress on the expression of preproTobHypSys-A ppTobHS-A) in tobacco plants was evaluated. Foliar application of methyl jasmonate preferentially induced the systemic expression of ppTobHS-A in leaves phyllotactically one position above-treated leaves. Abscisic acid strongly induced ppTobHS-A, but water-stress did not. Mechanical wound-induction of ppTobHS-A in young plantlets was rapidly (1 h) and simultaneously detected in wounded and upper unwounded leaves, whereas in older plants induction was slow (12 h) and localized. ppTobHS-A was induced in plants infested with Bemisia tabaci or damaged by herbivory with Manduca sexta larvae. Compared to mechanical wounding, larval herbivory induced a stronger and more stable expression of ppTobHS-A. Moreover, exposure to Manduca-damaged plants induced its expression in neighboring intact plants. In most treatments, the expression patterns of ppTobHS-A coincided with those of selected wound-responsive (WR) genes (e.g., PIOX, NtPI-I, TPI). This correlation was tighter in the wounded and MeJA-treated leaves, whereas in distal, undamaged leaves, it appeared to depend on the type of WR gene examined and on the type of damage sustained by the plant. These results are consistent with the perceived role of the TobHS in defense signaling.

Abscisic Acid↗
PubMed1997

Extensin from suspension-cultured potato cells: a hydroxyproline-rich glycoprotein, devoid of agglutinin activity.

Enhanced deposition and cross-linking of hydroxyproline-rich glycoproteins (HRGPs) in the plant cell wall is acknowledged to contribute to the formation of a resistant barrier against pathogen infection. We have isolated, from suspension-cultured potato (Solanum tuberosum L. cv. Desiree) cells, two forms of soluble HRGP, a cross-linked and a monomeric form; the latter can be converted to the cross-linked form by incubation with tomato extensin peroxidase and H2O2. The monomeric form was purified by Sephacryl S-200 gel-filtration, reverse-phase high-performance liquid chromatography and Mono-S cation-exchange chromatography into two isoforms (A, a minor form; B, a major form). The properties of the B isoform were further investigated. A quantitative enzyme-linked immunosorbent assay of the B isoform, using tomato extensin antiserum, showed a titration curve at a high antibody-dilution range comparable to that of purified tomato extension monomer (M.D. Brownleader and P.M. Dey, 1993, Planta 191: 457-469). The amino acid and carbohydrate compositions were similar to those of tomato extensin, but did not match well with the other two HRGPs from potato, potato lectin and potato bacterial agglutinin. These observations demonstrate the similarities of the B isoform to extensin. The homogeneity of the B isoform was demonstrated by its ability to be fully cross-linked in vitro, leaving no residual protein, into a high-molecular-weight form by the action of extensin peroxidase. The trifluoroacetic acid-deglycosylated sample migrated as a single protein band on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Moreover, SDS-PAGE and matrix-assisted laser desorption/ionisation-time of flight mass spectrometry indicated a molecular weight of approximately 67 kDa. Circular-dichroism spectroscopy demonstrated that the molecule possess an extended polyproline II helix conformation with no evidence of alpha-helix or beta- sheet secondary structure. In conclusion, we refer to this HRGP as potato extensin. As proposed for other extensins, potato extensin is likely to play a role in cell wall architecture and plant disease resistance.

Agglutinins↗
PubMed2006

Synthesis of novel potent hepatitis C virus NS3 protease inhibitors: discovery of 4-hydroxy-cyclopent-2-ene-1,2-dicarboxylic acid as a N-acyl-L-hydroxyproline bioisostere.

Potent tetrapeptidic inhibitors of the HCV NS3 protease have been developed incorporating 4-hydroxy-cyclopent-2-ene-1,2-dicarboxylic acid as a new N-acyl-l-hydroxyproline mimic. The hydroxycyclopentene template was synthesized in eight steps from commercially available (syn)-tetrahydrophthalic anhydride. Three different amino acids were explored in the P1-position and in the P2-position the hydroxyl group of the cyclopentene template was substituted with 7-methoxy-2-phenyl-quinolin-4-ol. The P3/P4-positions were then optimized from a set of six amino acid derivatives. All inhibitors were evaluated in an in vitro assay using the full-length NS3 protease. Several potent inhibitors were identified, the most promising exhibiting a K(i) value of 1.1nM.

Cyclopentanes↗
PubMed2004

Stereoselective synthesis of 3-hydroxyproline benzyl esters from N-protected beta-aminoaldehydes and benzyl diazoacetate.

The synthesis of a series of 3-hydroxyproline benzyl esters from alpha-alkyl and alpha-alkoxy N-protected aminoaldehydes with benzyl diazoacetate is described. Aldehydes with alpha-alkyl substituents afforded prolines as a single diastereomer with a trans-cis relative configuration in 14-77%. An alpha-tert-butyldimethylsilyloxy aminoaldehyde afforded a proline as a single diastereomer with a trans-trans relative configuration in 37% yield.

Journal Article↗
PubMed2006

Beta-glycosides of hydroxyproline via an umpolung approach.

Reaction of 1,2-O-dibutylstannylene-3,4-6-tri-O-benzyl-beta-D-mannopyranose with Nalpha-fluorenylmethoxycarbonyl-cis-4-trifluoromethanesulfonyloxyproline allyl ester led to formation of a beta-mannoside of trans-4-hydroxyproline. Subsequent manipulation of the C2 hydroxy group gave rise to beta-D-Glc and beta-D-GlcNAc derivatives.

Journal Article↗
PubMed1998

Induction of mRNA accumulation corresponding to a gene encoding a cell wall hydroxyproline-rich glycoprotein by fungal elicitors.

The Hrgp (hydroxyproline-rich glycoprotein) gene codes in maize for one of the most abundant proteins of the cell wall. HRGPs may contribute to the structural support of the wall and they have also been involved in plant defense mechanisms. This second aspect has been tested for the Hrgp gene in maize where, in contrast with the situation in dicot species, the gene is encoded by a single-copy sequence. Hrgp mRNA accumulation is induced in maize suspension-cultured cells by elicitors, isolated either from maize pathogenic or non-pathogenic fungi. The induction of Hrgp mRNA accumulation by elicitor extracted from Fusarium moniliforme has been studied in detail. The level of induction depends on elicitor concentration and remains high until at least 24 h. Ethylene and protein phosphorylation appear to be involved in the transduction pathway of Hrgp gene activation by the F. moniliforme elicitor but not by 5 microM methyl jasmonate or 1 mM salycilic acid. Different compounds known to participate in plant stress responses such as ascorbic acid or reduced glutathione have also a positive effect on Hrgp mRNA accumulation.

Acetates↗
PubMed2002

Rhizobium colonization induced changes in membrane-bound and soluble hydroxyproline-rich glycoprotein composition in pea.

Abundance and distribution of plant cell surface proteins of the hydroxyproline-rich glycoprotein (HRGP) class were studied in the pea-Rhizobium symbiosis using immunoblot analysis. The MAC 265-epitope was especially abundant in pea root nodules containing nitrogen-fixing Rhizobium bacteria. A 180-kDa MAC 265-HRGP dominated in pea shoot plasma membranes, while almost no MAC 265-HRGP was detected in root plasma membranes. We show here that a major difference between the plant-derived peribacteroid membrane of the symbiosomes and the root plasma membrane was the presence of a 100-kDa MAC 265-HRGP in the former. Arabinogalactan proteins (AGPs), as recognized by the monoclonal antibodies MAC 207 and JIM 8, were not detected in the peribacteroid membrane, while two isoforms (100 and 220 kDa) were detected in shoot and root plasma membranes. Specific MAC 265-HRGP isoforms were found in the peribacteroid space fraction of the symbiosomes and thus as soluble proteins in the interface between the symbionts. The abundance of the MAC 265-epitope was much reduced in non-nitrogen-fixing nodules when this phenotype resulted from a dicarboxylate transport mutation in Rhizobium. There was no reduction in the abundance of the MAC 265-epitope in non-fixing phenotypes resulting from a mutation in the plant. The results suggest that bacterial signals related to the bacterial ability to fix nitrogen, might be responsible for the regulation of HRGP expression in root nodules.

Journal Article↗
PubMed2005

The arabinogalactan-proteins from pressed juice of Echinacea purpurea belong to the hybrid class of hydroxyproline-rich glycoproteins.

Pressed juices from Echinacea purpurea are used as non-specific immunostimulants, and arabinogalactan-proteins (AGPs) are part of the active principle. An AGP fraction was isolated from pressed juice of E. purpurea by precipitation with ss-glucosyl Yariv reagent, followed by gel-permeation chromatography. Polyclonal antibodies directed against the carbohydrate moiety of this AGP fraction showed a preferential specificity for E. purpurea AGPs from pressed juice over those extracted from E. purpurea suspension culture and other plant species. Native AGPs purified from this AGP fraction by RP-HPLC were then deglycosylated for N-terminal protein sequencing resulting in the identification of three major polypeptides. They show characteristic motifs of classical AGPs but also some features of extensins, suggesting these may be "hybrid" hydroxyproline-rich glycoproteins (HRGPs).

Chromatography, High Pressure Liquid↗
PubMed1985

Accumulation of hydroxyproline-rich glycoprotein mRNAs in response to fungal elicitor and infection.

Hydroxyproline-rich glycoproteins (HRGPs) are important structural components of plant cell walls and also accumulate in response to infection as an apparent defense mechanism. Accumulation of HRGP mRNA in biologically stressed bean (Phaseolus vulgaris L.) cells was monitored by blot hybridization with (32)P-labeled tomato genomic HRGP sequences. Elicitor treatment of suspension-cultured cells caused a marked increase in hybridizable HRGP mRNA. The response was less rapid but more prolonged than that observed for mRNAs encoding enzymes of phytoalexin biosynthesis. HRGP mRNA also accumulated during race:cultivar-specific interactions between bean hypocotyls and the partially biotrophic fungus Colletotrichum lindemuthianum, the causal agent of anthracnose. In an incompatible interaction (host resistant) there was an early increase in HRGP mRNA correlated with expression of hypersensitive resistance; whereas, in a compatible interaction (host susceptible), marked accumulation of HRGP mRNA occurred as a delayed response at the onset of lesion formation. In both interactions, mRNA accumulation was observed in uninfected cells distant from the site of fungal inoculation, indicating intercellular transmission of an elicitation signal.

Journal Article↗
PubMed1992

Accumulation of cell wall hydroxyproline-rich glycoprotein mRNA is an early event in maize embryo cell differentiation.

The accumulation of the mRNA coding for a hydroxyproline-rich glycoprotein (HRGP), an abundant component of the wall from the cells of vegetative tissues, has been observed in maize embryo by in situ hybridization. The HRGP mRNA accumulates in the embryo axis and not in the scutellum and preferentially in dividing and provascular cells. The histone H4 mRNA is distributed in similar tissues but is restricted to defined groups of cells, indicating that these two gene products have a different steady-state level of accumulation during the cell cycle. The HRGP mRNA appears to be a useful marker for early formation of the vascular systems. The mRNA accumulation correlates in space and time with cells having a low content of cellulose in their walls, suggesting that the mRNA is produced in the early stages of cell wall formation before complete deposition of cellulose.

Cell Differentiation↗
PubMed1993

Developmental regulation and phytochrome-mediated induction of mRNAs encoding a proline-rich protein, glycine-rich proteins, and hydroxyproline-rich glycoproteins in Phaseolus vulgaris L.

We have studied developmental and light regulation of mRNAs encoding a putative cell wall proline-rich protein (PvPRP1), cell wall glycine-rich proteins (GRPs), and cell wall hydroxyproline-rich glycoproteins (HRGPs) in bean (Phaseolus vulgaris). Light increases the levels of these mRNAs 2- to 150-fold in highly spatially regulated patterns during seedling development. These mRNA changes include differential regulation of transcripts derived from the GRP and HRGP multigene families. In 6-day-old light-grown seedlings, the PvPRP1 and GRP1.0 mRNAs were most abundant in the apical region of hypocotyls, epicotyls, and roots. In contrast, several HRGP transcripts were most abundant in the mature region of hypocotyls and roots in light-grown seedlings. When etiolated 6-day-old seedlings were illuminated with white light for 8 hr, maximal accumulation of PvPRP1 and GRP1.0 mRNAs occurred in the apical hook, whereas HRGP and GRP1.8 mRNAs accumulated in the mature region of hypocotyls. Etiolated seedlings subjected to a pulse of red light accumulated PvPRP1, GRP, and HRGP mRNAs in the hypocotyls. Far-red light inhibited red light induction of these mRNAs, indicating a phytochrome-mediated process. The possible roles of PRPs, GRPs, and HRGPs in cell differentiation and photomorphogenesis are discussed.

Journal Article↗
PubMed1999

Identification of a UDP-GlcNAc:Skp1-hydroxyproline GlcNAc-transferase in the cytoplasm of Dictyostelium.

Skp1 is a cytoplasmic and nuclear protein required for the ubiquitination of cell cycle regulatory proteins and transcriptional factors. In Dictyostelium, Skp1 is modified by a linear pentasaccharide, Galalpha1-6Galalpha1-Fucalpha1-2Galbeta1-3Glc NAc, attached to a hydroxyproline (HyPro) residue at position 143. To study the formation of the GlcNAc-HyPro linkage, an assay was developed for the transfer of [(3)H]GlcNAc from UDP-[(3)H]GlcNAc to Skp1-HyPro-143 or a synthetic Skp1 4-HyPro peptide. The cytosolic but not the particulate fraction of the cell mediated transfer in a time-, concentration-, and HyPro-dependent fashion. Incorporated radioactivity was alkali-resistant and was recovered as GlcNH(2) after acid hydrolysis, consistent with linkage of GlcNAc to HyPro. The GlcNAc-transferase activity was purified 130,000-fold as a single component with a recovery of 5%. Key to the purification was the synthesis of a novel affinity resin linking UDP-GlcNAc at its 5-uridyl position. The purified activity had an apparent M(r) of approximately 45,000 by gel filtration, required dithiothreitol and a divalent cation, and consisted predominantly of a M(r) 51,000 band after SDS-polyacrylamide gel electrophoresis that was photoaffinity labeled with 5-(125)I-[3-(p-azidosalicylamido)-1-propenyl-UDP-GlcNAc in a UDP-GlcNAc-sensitive fashion. Its apparent K(m) values for UDP-GlcNAc and Skp1 were submicromolar. The presence of the enzyme in the cytosolic fraction, its dependence on a reducing environment, and its high affinity for UDP-GlcNAc strongly suggest that Skp1 is glycosylated by a HyPro GlcNAc-transferase that resides in the cytoplasm.

Animals↗
PubMed2001

Phytotoxic protein PcF, purification, characterization, and cDNA sequencing of a novel hydroxyproline-containing factor secreted by the strawberry pathogen Phytophthora cactorum.

A novel protein factor, named PcF, has been isolated from the culture filtrate of Phytophthora cactorum strain P381 using a highly sensitive leaf necrosis bioassay with tomato seedlings. Isolated PcF protein alone induced leaf necrosis on its host strawberry plant. The primary structure and cDNA sequence of this novel phytotoxic protein was determined, and BLAST searches of Swiss-Prot, EMBL, and GenBank(TM)/EBI data banks showed that PcF shared no significant homology with other known sequences. The 52-residue PcF protein, which contains a 4-hydroxyproline residue along with three S-S bridges, exhibits a high content of acidic sidechains, accounting for its isoelectric point of 4.4. The molecular mass of isolated PcF is 5,622 +/- 0.5 Da as determined by mass spectrometry and matches that calculated from the deduced amino acid sequence with cDNA sequencing. The cDNA sequence indicates that PcF is first produced as a larger precursor, comprising an additional N-terminal, 21-residue secretory signal peptide. Maturation of this protein involves the hydroxylation of proline 49, a feature that is unique among other known secreted fungal phytopathogenic proteins.

Amino Acid Sequence↗
PubMed2002

Molecular cloning and expression of a UDP-N-acetylglucosamine (GlcNAc):hydroxyproline polypeptide GlcNAc-transferase that modifies Skp1 in the cytoplasm of dictyostelium.

Skp1 is a ubiquitous eukaryotic protein found in several cytoplasmic and nuclear protein complexes, including the SCF-type E3 ubiquitin ligase. In Dictyostelium, Skp1 is hydroxylated at proline 143, which is then modified by a pentasaccharide chain. The enzyme activity that attaches the first sugar, GlcNAc, was previously shown to copurify with the GnT51 polypeptide whose gene has now been cloned using a proteomics approach based on a quadrupole/time-of-flight hybrid mass spectrometer. When expressed in Escherichia coli, recombinant GnT51 exhibits UDP-GlcNAc:hydroxyproline Skp1 GlcNAc-transferase activity. Based on amino acid sequence alignments, GnT51 defines a new family of microbial polypeptide glycosyltransferases that appear to be distantly related to the catalytic domain of mucin-type UDP-GalNAc:Ser/Thr polypeptide alpha-GalNAc-transferases expressed in the Golgi compartment of animal cells. This relationship is supported by the effects of site-directed mutagenesis of GnT51 amino acids associated with its predicted DXD-like motif, DAH. In contrast, GnT51 lacks the N-terminal signal anchor sequence present in the Golgi enzymes, consistent with the cytoplasmic localization of the Skp1 acceptor substrate and the biochemical properties of the enzyme. The first glycosylation step of Dictyostelium Skp1 is concluded to be mechanistically similar to that of animal mucin type O-linked glycosylation, except that it occurs in the cytoplasm rather than the Golgi compartment of the cell.

Amino Acid Sequence↗
PubMed1989

Specific expression of a novel cell wall hydroxyproline-rich glycoprotein gene in lateral root initiation.

A gene encoding a novel cell wall hydroxyproline-rich glycoprotein (HRGPnt3) was isolated from a genomic library of tobacco. The deduced protein (620 amino acids, Mr, 65,406) contains an amino-terminal hydrophobic signal peptide, is highly basic, and is rich in proline, although characteristic Ser-Pro4 repeats are found only beyond residue 204. At the carboxyl terminus, there is a 34-amino-acid unit repeated three times. Arginine is the predominant basic amino acid rather than lysine, as in other HRGPs. A second gene homologous to HRGPnt3 was revealed by Southern blot hybridization of tobacco genomic DNA. Northern blot hybridization identified a 1.9-kb transcript present at low levels in roots. To determine the underlying spatial pattern of expression, the HRGPnt3 promoter and the first 27 nucleotides of the open reading frame were fused to the beta-glucuronidase (GUS) reporter gene and transformed back into tobacco. Histochemical localization of GUS activity showed that the HRGPnt3 promoter was transiently induced in the pericycle and endodermis, specifically in the discrete, small subset of cells involved in the initiation of lateral roots. This pattern of expression, in cells destined to form the tip of the emerging lateral root, indicates that the encoded cell wall protein has a specialized structural function, possibly in the mechanical penetration of the cortex and epidermis of the main root, and that the HRGPnt3 promoter responds to an early morphogenetic signal for lateral root induction.

Amino Acid Sequence↗
PubMed1993

Complementary immunolocalization patterns of cell wall hydroxyproline-rich glycoproteins studied with the use of antibodies directed against different carbohydrate epitopes.

Antisera raised against the major hydroxyproline-rich glycoprotein (HRGP) in carrot (Daucus carota L.) taproot, extensin-1, and a minor HRGP, extensin-2, were characterized by western blot analysis, enzyme-linked immunosorbent assay, and periodate oxidation and found to be directed against carbohydrate epitopes shared by both glycoproteins. The anti-extensin-1 antibodies (gE1) target periodate-sensitive epitopes and may recognize the terminal alpha-1,3-arabinoside of extensin-1. The anti-extensin-2 antibodies (gE2) recognize periodate-insensitive epitopes, possibly binding the reducing, internal beta-1,2-arabinosides on the carbohydrate side chains. Despite the cross-reactivity of these antibodies, immunolocalization studies of carrot taproot and green bean (Phaseolus vulgaris L.) leaf tissues reveal a spatial segregation of gE1- and gE2-labeling patterns. The gE1 antibodies bind only to the cellulose-rich region of the cell wall (J.P. Staehelin and L.A. Stafstrom [1988] Planta 174: 321-332), whereas gE2 labeling is restricted to the expanded middle lamella at three cell junctions. Periodate oxidation of nonosmicated, thin-sectioned tissue abolishes gE1 labeling but leads to labeling of the entire cell wall by gE2, presumably as a result of unmasking cryptic epitopes on extensin-1 in the cellulose layer. Purified extensin-2 protein is more efficient than extensin-1 protein at agglutinating avirulent Pseudomonas strains lacking extracellular polysaccharide. Our results indicate that extensin-2 does not form a heterologous HRGP network with extensin-1 and that, in contrast to extensin-1, which appears to serve a structural role, extensin-2 could participate in passive defense responses against phytopathogenic bacteria.

Agglutination Tests↗
PubMed1995

Stress activation of a bean hydroxyproline-rich glycoprotein promoter is superimposed on a pattern of tissue-specific developmental expression.

The HRGP4.1 gene, which encodes a cell wall hydroxyproline-rich glycoprotein, was isolated from a genomic library of bean (Phaseolus vulgaris L.). Two transcripts, one induced by wounding and one by elicitation, were transcribed from the same initiation site. The gene encodes a polypeptide of 580 amino acids with the amino terminal half consisting of repeats of the sequence serine-(proline)4-lysine-histidine-serine-(proline)4-(tyrosine)3-histidi ne and the carboxyl-terminal half composed of repeats of the sequence serine-(proline)4-valine-tyrosine-lysine-tyrosine-lysine. A 964-bp upstream promoter fragment was translationally fused to the beta-glucuronidase reporter gene (Escherichia coli uidA) and transferred into tobacco by Agrobacterium tumefaciens-mediated leaf disc transformation. Analysis of beta-glucuronidase activity showed that wounding caused local activation of the HRGP4.1 promoter in the phloem. Infection by tobacco mosaic virus was a less effective inducer than wounding. Stress induction was superimposed on tissue-specific developmental expression in stem nodes and root tips, suggesting that HRGP4.1 may have specific structural roles in development as well as protective functions in defense. Deletion analysis showed that control of tissue specificity and wound inducibility lies in a region between -94 and -251 relative to the transcription start site and that activation by infection lies outside that region.

Agrobacterium tumefaciens↗
PubMed1998

Expression of a Soybean Hydroxyproline-Rich Glycoprotein Gene Is Correlated with Maturation of Roots

A novel extensin gene has been identified in soybean (Glycine max L.) that encodes a hydroxyproline-rich glycoprotein (SbHRGP3) with two different domains. In this study expression of SbHRGP3 was investigated during soybean root development. SbHRGP was expressed in roots of mature plants, as well as seedlings, and showed a distinct pattern of expression during root development. The expression of SbHRGP3 increased gradually during root development of seedlings and reached a maximum while the secondary roots were maturing. The maximum expression level was contributed mainly by the secondary roots rather than by the primary root. Furthermore, expression of SbHRGP3 was preferentially detected in the regions undergoing maturation of the primary and secondary roots. These results imply that the expression of SbHRGP3 is regulated in an organ- and development-specific manner and that in soybean SbHRGP3 expression may be required for root maturation, presumably for the cessation of root elongation. Wounding and sucrose in combination enhanced expression of SbHRGP3 in roots, whereas both wounding and sucrose were required for the expression of SbHRGP3 in leaves.

Journal Article↗