Molecular cloning and epitope analysis of the peanut allergen Ara h 3.
Peanut allergy is a significant IgE-mediated health problem because of the increased prevalence, potential severity, and chronicity of the reaction. Following our characterization of the two peanut allergens Ara h 1 and Ara h 2, we have isolated a cDNA clone encoding a third peanut allergen, Ara h 3. The deduced amino acid sequence of Ara h 3 shows homology to 11S seed-storage proteins. The recombinant form of this protein was expressed in a bacterial system and was recognized by serum IgE from approximately 45% of our peanut-allergic patient population. Serum IgE from these patients and overlapping, synthetic peptides were used to map the linear, IgE-binding epitopes of Ara h 3. Four epitopes, between 10 and 15 amino acids in length, were found within the primary sequence, with no obvious sequence motif shared by the peptides. One epitope is recognized by all Ara h 3-allergic patients. Mutational analysis of the epitopes revealed that single amino acid changes within these peptides could lead to a reduction or loss of IgE binding. By determining which amino acids are critical for IgE binding, it might be possible to alter the Ara h 3 cDNA to encode a protein with a reduced IgE-binding capacity. These results will enable the design of improved diagnostic and therapeutic approaches for food-hypersensitivity reactions. (+info)
Cell adhesion activity for murine carcinoma cells of a wheat germ 55-kDa protein with binding affinity for animal extracellular matrix proteins.
A wheat germ 55-kDa protein was isolated by affinity chromatography with Matrigel immobilized on agarose, followed by preparative gel electrophoresis. This Matrigel-binding protein designated as WG-55 had an amino-terminal amino acid sequence which is identical to that of a putative mature form of wheat storage protein Gbl 1. WG-55 reacted with concanavalin A, indicating its glycoprotein nature as expected from the amino acid sequence of Gbl 1. As expected, similarly, WG-55 exhibited RGD-dependent cell adhesion activity for murine carcinoma cells. These data suggest that WG-55 or mature Gbl 1 protein may play a role in plant cell adhesion. (+info)
A pea nuclear protein that is induced by dehydration belongs to the vicilin superfamily.
The purification to homogeneity of p16, a protein with an electrophoretic mobility compatible with an apparent molecular mass of 16 kDa, from nuclei of ungerminated pea embryonic axes is described. A cDNA clone of its gene, which was designated psp54, was also isolated. The psp54 cDNA contains an open reading frame coding for a 54.4-kDa polypeptide (p54). p16 corresponds to the C-terminal third of p54, although the mechanisms by which the primary polypeptide could be processed are not yet known. The sequence of p54 is 60% identical with that of the precursor of a sucrose-binding soybean protein, and, to a lesser extent (31-34%), it shares homology with some storage proteins. p16 is also 30% homologous with Nhp2p, a yeast nuclear protein. The psp54 gene, present in a single copy in pea genome, starts being expressed during seed desiccation. Soon after rehydration in seed germination, p54 mRNA disappears and is no longer detectable in vegetative tissues, except in response to hydric stress (exposure to abscisic acid, osmolites or desiccation). p16 can be recovered from nuclei cross-linked to histone H3, when the disulfide bridges that occur in vivo are preserved. On the other hand, p16 shares some properties with dehydrins, which are thought to protect cellular structures against desiccation. We propose that the possible precursor polypeptide p54 belongs to the vicilin superfamily, members of which play a variety of roles. The function of p16 may be related to the protection of chromatin structure against desiccation during seed development. (+info)
Vacuolar storage proteins are sorted in the cis-cisternae of the pea cotyledon Golgi apparatus.
Developing pea cotyledons contain functionally different vacuoles, a protein storage vacuole and a lytic vacuole. Lumenal as well as membrane proteins of the protein storage vacuole exit the Golgi apparatus in dense vesicles rather than in clathrin-coated vesicles (CCVs). Although the sorting receptor for vacuolar hydrolases BP-80 is present in CCVs, it is not detectable in dense vesicles. To localize these different vacuolar sorting events in the Golgi, we have compared the distribution of vacuolar storage proteins and of alpha-TIP, a membrane protein of the protein storage vacuole, with the distribution of the vacuolar sorting receptor BP-80 across the Golgi stack. Analysis of immunogold labeling from cryosections and from high pressure frozen samples has revealed a steep gradient in the distribution of the storage proteins within the Golgi stack. Intense labeling for storage proteins was registered for the cis-cisternae, contrasting with very low labeling for these antigens in the trans-cisternae. The distribution of BP-80 was the reverse, showing a peak in the trans-Golgi network with very low labeling of the cis-cisternae. These results indicate a spatial separation of different vacuolar sorting events in the Golgi apparatus of developing pea cotyledons. (+info)
Vicilins (7S storage globulins) of cowpea (Vigna unguiculata) seeds bind to chitinous structures of the midgut of Callosobruchus maculatus (Coleoptera: Bruchidae) larvae.
The presence of chitin in midgut structures of Callosobruchus maculatus larvae was shown by chemical and immunocytochemical methods. Detection by Western blotting of cowpea (Vigna unguiculata) seed vicilins (7S storage proteins) bound to these structures suggested that C. maculatus-susceptible vicilins presented less staining when compared to C. maculatus-resistant vicilins. Storage proteins present in the microvilli in the larval midgut of the bruchid were recognized by immunolabeling of vicilins in the appropriate sections with immunogold conjugates. These labeling sites coincided with the sites labeled by an anti-chitin antibody. These results, taken together with those previously published showing that the lower rates of hydrolysis of variant vicilins from C. maculatus-resistant seeds by the insect's midgut proteinases and those showing that vicilins bind to chitin matrices, may explain the detrimental effects of variant vicilins on the development of C. maculatus larvae. (+info)
Conformational change in a single molecular species, beta3, of beta-conglycinin in acidic ethanol solution.
Several physicochemical experiments were done to obtain further information on the conformational changes occurring in beta-conglycinin in acidic-ethanol solution, using a single molecular species of this protein, beta3. By far-UV circular dichroism (CD), a transition from beta-sheet to alpha-helical structure was observed upon addition of acidic-ethanol, and the alpha-helix content was found to reach 76% in 70% ethanol (pH 2). From analyses of near-UV CD and difference absorption spectra, it was found that the tertiary structure of the beta3 species was significantly altered at ethanol concentrations between 10 and 20%. The profiles of binding of 1-anilinonaphthalene-8-sulfonic acid to the beta3 species during acidic-ethanol denaturation were indicative of the existence of intermediate conformers in the molten globule-like denaturation state. By measuring Fourier transform infrared spectra and estimating the Stokes radius by dynamic light scattering, the beta3 molecules were found to aggregate with an increase in ethanol concentration. (+info)
Cosuppression of the alpha subunits of beta-conglycinin in transgenic soybean seeds induces the formation of endoplasmic reticulum-derived protein bodies.
The expression of the alpha and alpha' subunits of beta-conglycinin was suppressed by sequence-mediated gene silencing in transgenic soybean seed. The resulting seeds had similar total oil and protein content and ratio compared with the parent line. The decrease in beta-conglycinin protein was apparently compensated by an increased accumulation of glycinin. In addition, proglycinin, the precursor of glycinin, was detected as a prominent polypeptide band in the protein profile of the transgenic seed extract. Electron microscopic analysis and immunocytochemistry of maturing transgenic soybean seeds indicated that the process of storage protein accumulation was altered in the transgenic line. In normal soybeans, the storage proteins are deposited in pre-existing vacuoles by Golgi-derived vesicles. In contrast, in transgenic seed with reduced beta-conglycinin levels, endoplasmic reticulum (ER)-derived vesicles were observed that resembled precursor accumulating-vesicles of pumpkin seeds and the protein bodies accumulated by cereal seeds. Their ER-derived membrane of the novel vesicles did not contain the protein storage vacuole tonoplast-specific protein alpha-TIP, and the sequestered polypeptides did not contain complex glycans, indicating a preGolgi and nonvacuolar nature. Glycinin was identified as a major component of these novel protein bodies and its diversion from normal storage protein trafficking appears to be related to the proglycinin buildup in the transgenic seed. The stable accumulation of proteins in a protein body compartment instead of vacuolar accumulation of proteins may provide an alternative intracellular site to sequester proteins when soybeans are used as protein factories. (+info)
Protease C2, a cysteine endopeptidase involved in the continuing mobilization of soybean beta-conglycinin seed proteins.
The protease that degrades the beta subunit of the soybean (Glycine max (L.) Merrill) storage protein beta-conglycinin was purified from the cotyledons of seedlings grown for 12 days. The enzyme was named protease C2 because it is the second enzyme to cleave the beta-conglycinin storage protein, the first (protease C1) being one that degrades only the alpha' and alpha subunits of the storage protein to products similar in size and sequence to the remaining intact beta subunit. Protease C2 activity is not evident in vivo until 4 days after imbibition of the seed. The 31 kDa enzyme is a cysteine protease with a pH optimum with beta-conglycinin as substrate of 5.5. The action of protease C2 on native beta-conglycinin produces a set of large fragments (52-46 kDa in size) and small fragments (29-25 kDa). This is consistent with cleavage of all beta-conglycinin subunits at the region linking their N- and C-domains. Protease C2 also cleaves phaseolin, the Phaseolus vulgaris vicilin homologous to beta-conglycinin, to fragments in the 25-28 kDa range. N-Terminal sequences of isolated beta-conglycinin and phaseolin products show that protease C2 cleaves at a bond within a very mobile surface loop connecting the two compact structural domains of each subunit. The protease C2 cleavage specificity appears to be dictated by the substrate's three-dimensional structure rather than a specificity for a particular amino acid or sequence. (+info)