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Hydroxyproline-containing proteins increase markedly in the cell walls of the Alaska pea epicotyl during the transition of rapidly elongating tissue into non-elongating, mature tissue. The increase in these proteins may be a factor in the cessation of cell elongation.
The hydroxyproline-O-arabinosyl linkage is present in cell walls of selected tissues representing green plants from algae to angiosperms.
Isopycnic equilibrium centrifugation techniques were used to determine whether any horseradish (Amoracia lapathifolia) peroxidase isozymes were associated with hydroxyproline containing moieties. Purified peroxidase, horseradish root extracts, and peroxidase isozymes released from horseradish root cell walls were tested. In no case could any peak of peroxidase activity be found to band with hydroxyproline.A fluorimetric method for measurement of peroxidase activity was used to determine quantitatively the amount of total peroxidase located on horseradish root cell walls. Twenty per cent of the total peroxidase is found in the cell wall fraction after extraction; 93% of this cell wall associated peroxidase can be removed by washing with 2 m NaCl. Some peroxidase isozymes released by salt washing are not found in the cytoplasmic extract. This indicates that not all of the ionically bound peroxidase represents cytoplasmic contamination. The 1.4% of the total peroxidase activity can thus be considered tightly bound to the cell wall. Of this portion, 75% can be solubilized by treatment with a cellulase preparation. One isozyme is released which was not present in the original cytoplasmic extract.
Hydroxyproline-poor glycoprotein contains a single polypeptide chain with lysine at the N-terminus. Removal of carbohydrate attached to serine by alkali treatment produces two polypeptide fractions. Labeling with (35)S indicates that most serine residues having a carbohydrate substituent removed by alkali occur on the polypeptide fraction of lower molecular weight. Following alkali treatment, two additional N-terminal amino acids, proline and glycine, were detected suggesting that alkali treatment also cleaves peptide bonds. Methylation analysis of native and degraded glycoproteins, extracted 24, 27, and 36 hours after wounding, demonstrates the following structural features of carbohydrate attached to serine. Arabinose may be (1 --> 2)-, (1 --> 3)-, or (1 --> 5)-linked, glucose occurs as a chain of beta-(1 --> 4)-linked residues, and galactose occurs as a nonreducing terminal unit.
A protein, extracted from Katahdin potato (Solanum tuberosum L. cv ;Katahdin') tubers and purified by ion exchange chromatography and gel filtration, agglutinates avirulent strains of the bacterial wilt pathogen, Pseudomonas solanacearum, but only weakly agglutinates virulent strains. The agglutinin has very low hemagglutinating activity (in contrast to potato lectin) and is a glycoprotein containing about 61% carbohydrate. The carbohydrate moiety contains 91% (weight%) arabinose, 5% galactose, 3% glucose, and 1% glucosamine. The protein portion is rich in hydroxyproline (42%), lysine (16%), serine (9%), and proline (9%). The entire agglutinin has a molecular weight of 91,000 +/- 5,000 and is very basic (pI > 11). Shape estimations based on the concentration dependence of the sedimentation coefficient, the high viscosity ([eta] = 92.7), the frictional coefficient (f/f(o) = 2.15), and axial ratio (a/b = 25) indicate that the agglutinin is a prolate ellipsoid.
Treatment of melon hypocotyls or petioles with an elicitor from Colletotrichum lagenarium, a fungal pathogen of melons, causes an initial transitory inhibition of protein synthesis and, after 18 hours, induces the synthesis of a plant cell wall hydroxyproline-rich glycoprotein (HRGP). Microgram amounts of elicitor are sufficient for maximum elicitation of HRGP when the elicitor is injected into hypocotyls. High elicitor concentrations have a strong inhibitory effect on total protein synthesis. Ethylene is increased early in elicitor-treated plant material, and may be involved in HRGP elicitation. In the presence of aminoethoxyvinylglycine, an inhibitor of ethylene synthesis, both elicitor-induced ethylene and elicitor-induced HRGP are inhibited. On the other hand, 1-aminocyclopropane-1-carboxylic acid, the direct precursor of ethylene, triggers the synthesis of HRGP to the same extent as the elicitor of C. lagenarium, and partly restores in elicitor-treated petioles the synthesis of ethylene and of HRGP after previous inhibition by aminoethoxyvinylglycine. Elicitation of HRGP occurs in other systems, such as soybeans when inoculated with an elicitor from Phytophtora megasperma f. sp. glycinea, and when melons are incubated with an elicitor isolated from their cell walls.
The distribution of transcripts encoding hydroxyproline-rich glycoproteins in hypocotyls of Phaseolus vulgaris L. infected with Colletotrichum lindemuthianum was examined by in situ hybridization to tissue sections. The expression of hypersensitive resistance in an incompatible interaction was accompanied by a massive early accumulation of transcripts in the epidermal, cortical, and perivascular parenchymal tissues immediately adjacent to the inoculation site. In a compatible interaction, there was no accumulation of transcripts in the epidermal and cortical tissues even though fungal hyphae ramified throughout these tissues. However, transcripts accumulated at a later stage in the perivascular tissue directly below the site of infection and in tissue several millimeters from the inoculation site. Thus, there is a spatial and tissue-specific counterpart to the differential timing of transcript accumulation in incompatible versus compatible interactions (AM Showalter, JN Bell, CL Cramer, JA Bailey, CJ Lamb [1985] Proc Natl Acad Sci USA 82: 6551-6555). These differences in the spatial distribution and tissue specificity of transcript accumulation imply the differential induction of signaling systems involved in race:cultivar-specific interactions.
A novel hydroxyproline-rich glycoprotein (SbHRGP3) that consists of two different domains is encoded by an extensin gene from soybean. The first domain (domain 1) located at the N terminus is composed of 11 repeats of Ser-Pro4-Lys-His-Ser-Pro4-Tyr3-His, whereas the second domain (domain 2) at the C terminus contains five repeats of Ser-Pro4-Val-Tyr-Lys-Tyr-Lys-Ser-Pro4-Tyr-Lys-Tyr-Pro-Ser-Pro5-Tyr-Lys-T yr- Pro-Ser-Pro4-Val-Tyr-Lys-Tyr-Lys. These two repeat motifs are organized in an extremely well-ordered pattern in each domain, which suggests that SbHRGP3 belongs to a new group of proteins having the repeat motifs of two distinct groups of dicot extensins. The expression of the SbHRGP3 gene increased with seedling maturation, and its expression was relatively high in the mature regions of the hypocotyl and in the root of soybean seedlings. An SbHRGP3-beta-glucuronidase (SbHRGP3-GUS) chimeric gene was constructed and expressed in transgenic tobacco plants. The expression of the SbHRGP3-GUS gene was not induced by wounding alone in transgenic tobacco plants; sucrose was also required. Expression was specific to phloem tissues and cambium cells of leaves and stems. In transgenic tobacco seedlings, SbHRGP3-GUS gene expression was activated by the maturation of the primary root and then inactivated; however, reactivation was specifically at the epidermis of the zone from which the lateral root was to be initiated. Its reactivation occurred just before the lateral root initiation. These results indicate that the SbHRGP3 gene in different tissues responds to different signals.
Syntheses are described of the Hyp3-tuftsin analogue and of its derivatives alpha- or beta-O-glycosylated at the side chain function of the hydroxyproline residue. The carbohydrate-free tetrapeptide was prepared by reacting Z-Thr-Lys(Z)-OH with H-Hyp-Arg(NO2)-OBzl by the mixed anhydride procedure. In the synthesis of the alpha-glycosylated analogue the O-glycosyl amino acid was incorporated by reacting Boc-(Glc alpha+beta)Hyp-OH with H-Arg(NO2)-OBzl through the same procedure. The alpha-glucosylated dipeptide was isolated from the diastereomeric mixture, selectively deblocked, and acylated with Z-Thr-Lys(Z)-OH by the mixed anhydride procedure. In the preparation of the beta-glucosylated analogue the BOP procedure was used for reacting Boc-[Glc(Ac)4 beta]Hyp-OH with H-Arg(NO)2-OBzl was well as for the final coupling to tetrapeptide. Removal of protecting groups from crude tetrapeptides was achieved by catalytic hydrogenation. Deacetylation of the sugar moiety of the beta-glucosylated tetrapeptide was achieved by treatment with sodium methoxide in methanol. The synthetic compounds were isolated by ion exchange chromatography, and characterized by elemental analysis, amino acid analysis, optical rotation and proton NMR. Their capacity to evoke the release of interleukin 1 from mouse peritoneal macrophages and to modulate immunogenic activity of antigen-fed cells was evaluated, in comparison with tuftsin and rigin. All of the analogues were found to possess tuftsin-like activity.
The nitrogen content, distribution, and amino acid composition of protein material were determined in wood and lignin of Fagus sylvatica. The data indicated that the nitrogen originated from hydroxyproline-rich cell wall glycoprotein, about half of which may be bound to the lignin polymer. The implications for lignocellulose biodegradation are discussed.
We have characterized three different transcripts induced by fungal elicitor, wounding, or infection which encode apoproteins of cell wall hydroxyproline-rich glycoproteins involved in plant defense against infection. The proteins encoded by two of these transcripts contain a proline-rich domain involving tandem repetition of the 16-amino-acid unit Tyr3-Lys-Ser-Pro4-Ser-Pro-Ser-Pro4. The third transcript encodes a protein with a proline-rich domain involving a variant of this 16-mer canonical repeat: Tyr3-His-Ser-Pro4-Lys-His-Ser-Pro4. Each transcript is encoded by a separate gene present at single or low copy number in the haploid genome. These transcripts exhibit markedly different patterns of accumulation in different stress conditions, indicating the operation of several distinct intercellular stress signal systems in higher plants.
Hydroxyproline 2-epimerase of Pseudomonas putida was purified to homogeneity by an improved procedure. The native enzyme consists of two probably identical subunits. Alkylation of the active site with labeled reagents resulted in the loss of 80-85% of the activity but the incorporation of only one alkyl group even though the active site contains a Cys residue from each of the two subunits. This result suggests that the enzyme shows half-site reactivity. The labeled enzyme was further subjected to exhaustive alkylation with unlabeled iodoacetate, permitting tryptic hydrolysis and isolation of an active site peptide in 30% yield. The specific radioactivity of the peptide was consistent with the first result, that only 1 mol of alkyl group was initially incorporated into active site. The active site peptide (14 residues) was sequenced and found to possess homology with the clostridial proline racemase.
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