The sequence of a gene encoding convicilin from pea (Pisum sativum L.) shows that convicilin differs from vicilin by an insertion near the N-terminus

Pea and lentil 7S globulin crystal structures with comparative immunoglobulin epitope mapping

Legumes represent an affordable high protein, nutrient dense food source. However, the vast majority of legume crops contain proteins that are known allergens for susceptible individuals. These include proteins from the 7S globulin family, which comprise a vast majority of seed storage proteins. Here, the crystal structures of 7S globulins from Pisum sativum L. (pea) and Lens culinaris Medicus (lentil) are presented for the first time, including pea vicillin and convicilin, and lentil vicilin. All three structures maintain the expected 7S globulin fold, with trimeric quaternary structure and monomers comprised of β-barrel N- and C-modules. The potential impact of sequence differences on structure and packing in the different crystal space groups is noted, with potential relevance to packing upon seed deposition. Mapping on the obtained crystal structures highlights significant Ig epitope overlap between pea, lentil, peanut and soya bean and significant coverage of the entire seed storage protein, emphasizing the challenge in addressing food allergies. How recently developed biologicals might be refined to be more effective, or how these seed storage proteins might be modified in planta to be less immuno-reactive remain challenges for the future. With legumes representing an affordable, high protein, nutrient dense food source, this work will enable important research in the context of global food security and human health on an ongoing basis.

Pea (Pisum sativum) allergy in children: Pis s 1 is an immunodominant major pea allergen and presents IgE binding sites with potential diagnostic value

BACKGROUND

Food allergy to pea (Pisum sativum) has been rarely studied in children at the clinical and molecular levels.

OBJECTIVE

To elucidate the allergenic relevance and diagnostic value of pea 7S globulin Pis s 1, nsLTP, and 2S albumins PA1 and PA2 in children.

METHODS

Children with pea-specific IgE ≥ 0.35 kUA /L and clinical evidence of pea allergy or tolerance were included in the study. IgE binding against pea total protein extract, recombinant (r) rPis s 1, rPA1, rPA2, and natural nsLTP was analysed using IgE immunoblot/inhibition. Mediator release potency was investigated in passively sensitized rat basophil leukaemia (RBL) 2H3-cells. IgE binding to synthetic overlapping peptides of Pis s 1 was detected on multipeptide microarrays.

RESULTS

19 pea-sensitized children were included, 14 with doctors' diagnosed allergy and 5 with tolerance to pea (median age 3.5 and 4.5 years, respectively). 11/14 (78%) pea-allergic and 1/5 (20%) tolerant children were sensitized to Pis s 1. Under the reducing conditions of immunoblot analysis, IgE binding to rPA1 was negligible, sensitization to rPA2 and nsLTP undetectable. Compared to pea total protein extract, rPis s 1 displayed on average 58% IgE binding capacity and a 20-fold higher mediator release potency. Selected Pis s 1-related peptides displayed IgE binding in pea-allergic but not in pea-tolerant children.

CONCLUSIONS AND CLINICAL RELEVANCE

In this study group, Pis s 1 is a major immunodominant allergen in pea-allergic children. Evidence for sensitization to nsLTP and 2S albumins was low but requires further verification with regard to conformational epitopes. Recombinant Pis s 1 and related peptides which were exclusively recognized by pea-allergic children may improve in vitro diagnosis of pea allergy once verified in prospective studies with larger study groups.

Modification of pea protein isolate for ultrasonic encapsulation of functional liquids

This study reports on the ultrasonic processing of pea protein isolate (PPI) in phosphate-buffered saline (PBS, pH 7.4) and Tris/HCl (pH 8) buffer systems in order to modify its properties for use in the encapsulation of functional liquids.

Mobilization of seed protein reserves

The mobilization of seed storage proteins upon seed imbibition and germination is a crucial process in the establishment of the seedling. Storage proteins fold compactly, presenting only a few vulnerable regions for initial proteolytic digestion. Evolutionarily related storage proteins have similar three-dimensional structure, and thus tend to be initially cleaved at similar sites. The initial cleavage makes possible subsequent rapid and extensive breakdown catalyzed by endo- and exopeptidases. The proteolytic enzymes that degrade the storage proteins during mobilization identified so far are mostly cysteine proteases, but also include serine, aspartic and metalloproteases. Plants often ensure early initiation of storage protein mobilization by depositing active proteases during seed maturation, in the very compartments where storage proteins are sequestered. Various means are used in such cases to prevent proteolytic attack until after imbibition of the seed with water. This constraint, however, is not always enforced as the dry seeds of some plant species contain proteolytic intermediates as a result of limited proteolysis of some storage proteins. Besides addressing fundamental questions in plant protein metabolism, studies of the mobilization of storage proteins will point out proteolytic events to avoid in large-scale production of cloned products in seeds. Conversely, proteolytic enzymes may be applied toward reduction of food allergens, many of which are seed storage proteins.

Vicilin genes of Vigna luteola: structure, organization, expression, and variation

Two different but related sequences that encode Vigna luteola 7S vicilins were isolated and characterized. The sequences differ by two nucleotide substitutions, each of which results in an amino acid replacement. This low level of divergence suggests that a recent gene duplication has occurred. Both variants are expressed in cDNA populations; therefore, neither gene is a pseudogene. Both copies were present in all individuals (72) analyzed using real-time PCR and TaqMan probes. Segregation was not observed. The two sequences are not independent alleles. Vicilin genomic sequences of 11 specimens from six geographic locations were determined. No polymorphic sites were identified in either of the two gene copies. This lack of polymorphism suggests that either a population bottleneck or selection has occurred. The genetic structure, expression patterns, and protein composition of the V. luteola vicilins were compared to those of other legume vicilins.

Seed storage protein gene promoters contain conserved DNA motifs in Brassicaceae, Fabaceae and Poaceae

BACKGROUND

Accurate computational identification of cis-regulatory motifs is difficult, particularly in eukaryotic promoters, which typically contain multiple short and degenerate DNA sequences bound by several interacting factors. Enrichment in combinations of rare motifs in the promoter sequence of functionally or evolutionarily related genes among several species is an indicator of conserved transcriptional regulatory mechanisms. This provides a basis for the computational identification of cis-regulatory motifs.

RESULTS

We have used a discriminative seeding DNA motif discovery algorithm for an in-depth analysis of 54 seed storage protein (SSP) gene promoters from three plant families, namely Brassicaceae (mustards), Fabaceae (legumes) and Poaceae (grasses) using backgrounds based on complete sets of promoters from a representative species in each family, namely Arabidopsis (Arabidopsis thaliana (L.) Heynh.), soybean (Glycine max (L.) Merr.) and rice (Oryza sativa L.) respectively. We have identified three conserved motifs (two RY-like and one ACGT-like) in Brassicaceae and Fabaceae SSP gene promoters that are similar to experimentally characterized seed-specific cis-regulatory elements. Fabaceae SSP gene promoter sequences are also enriched in a novel, seed-specific E2Fb-like motif. Conserved motifs identified in Poaceae SSP gene promoters include a GCN4-like motif, two prolamin-box-like motifs and an Skn-1-like motif. Evidence of the presence of a variant of the TATA-box is found in the SSP gene promoters from the three plant families. Motifs discovered in SSP gene promoters were used to score whole-genome sets of promoters from Arabidopsis, soybean and rice. The highest-scoring promoters are associated with genes coding for different subunits or precursors of seed storage proteins.

CONCLUSION

Seed storage protein gene promoter motifs are conserved in diverse species, and different plant families are characterized by a distinct combination of conserved motifs. The majority of discovered motifs match experimentally characterized cis-regulatory elements. These results provide a good starting point for further experimental analysis of plant seed-specific promoters and our methodology can be used to unravel more transcriptional regulatory mechanisms in plants and other eukaryotes.

A comparative study of convicilin storage protein gene sequences in species of the tribe Vicieae

Convicilins, a set of seed storage proteins, differ from vicilins, a related group of seed storage proteins, mainly because of the presence of the N-terminal extension, an additional sequence of amino acids in the sequence corresponding to the first exon. Convicilins have been described only in species of the legume tribe Vicieae. One or two genes for convicilins have been identified in most species of this tribe. The genus Pisum is the main exception, since two genes have been identified in most of its species. Thirty-four new convicilin gene sequences from 29 different species (Lathyrus, Lens, Pisum, and Vicia spp.) have been analyzed here. Convicilin gene sequences are generally organized in 6 exons, but in some instances one of the internal introns (2nd or 4th) is lost. In these 29 species, the N-terminal extension is formed by a stretch of 99 to 196 amino acids particularly rich in polar and charged amino acids (on average, it contains 29.43% glutamic acid and 15.38% arginine residues). This N-terminal extension has the characteristics of an intrinsically unstructured region (IUR), one of the categories of protein "degenerate sequences". A comparative analysis indicates that the N-terminal extension sequence has evolved faster than the surrounding sequence, which is common to all vicilins, and it evolved mainly through a series of duplications of short internal sequences and triplet expansions, the predominant one being GAA. This agrees with the evolution of IURs, which is faster than the evolution of surrounding sequences and is mainly due to replication slippage and unequal crossover recombination. Alternative maximum-likelihood trees of phylogenetic relationships among the 29 Vicieae species based on the convicilin exon sequences are presented and discussed.

Determination of pepsin-susceptible and pepsin-resistant epitopes in native and heat-treated peanut allergen Ara h 1

This study was aimed at the determination of the pepsin-susceptible and pepsin-resistant epitopes in native and heat-treated Ara h 1, a major allergen from peanuts. Both the oligomeric structure and the trimeric structure of the allergen were investigated. Under the in vitro conditions applied, oligomeric Ara h 1, either unheated or preheated, was hydrolyzed by pepsin at a lower rate than trimeric Ara h 1. Peptides with relatively high molecular masses were shown to be able to bind IgE, whereas peptides with lower molecular masses (<2 kDa) did not. In these latter fractions, fragments of 15 previously published epitopes of mature Ara h 1 were identified. As a result, these epitopes are not likely responsible for the induction of systemic food allergic reactions to peanuts. Using sequential chymotrypsin digestion, the pepsin-resistant IgE-binding peptides were deduced to contain the previously identified intact epitopes EDWRRPSHQQ (amino acids 50-59) and PRKIRPEG (amino acids 60-67). The presence of four additional earlier published intact epitopes (covering amino acids 6-13, 14-21, 24-31, and 40-47) on the pepsin-resistant peptides could be neither deduced nor ruled out. The two deduced and four possible pepsin-resistant epitopes are all situated in the N-terminal part of Ara h 1, which does not show homology with other vicilin proteins. Consequently, this unique N-terminal part of Ara h 1 is proposed to be responsible for the allergen's ability to induce systemic allergic reactions.

Genetic variation in pea seed globulin composition

A quantitative characterization of seeds from 59 pea (Pisum sativum L.) lines and relative taxa with various external characteristics and wide geographical origin was performed to explore the genetic variation of pea concerning its starch and protein contents and globulin composition. Pea lines, which produce round, wrinkled, flat, and round-dimpled seeds, have starch as the major reserve, with an average content of 46%. Protein content varied from 13.7 to 30.7% of the seed dry matter, with an overall average of 22.3%. Densitometric quantification of the individual globulins (legumin, vicilin, convicilin, and globulin-related proteins) based on SDS-PAGE gels showed no lines lacking any particular globulin. Among the lines tested, variation was shown in both their total globulins content and their globulin composition. The total globulin content ranged from 49.2 to 81.8% of the total pea protein extract (TPPE). Legumin content varied between 5.9 and 24.5% of the TPPE. Vicilin was the most abundant protein of pea, and its content varied between 26.3 and 52.0% of the TPPE. Both processed and nonprocessed vicilins occurred. The processed vicilin was the predominant one, with values between 17.8 and 40.8%, whereas the nonprocessed ones constituted between 3.1 and 13.5% of the TPPE. Convicilin was the least abundant globulin, and its content ranged from 3.9 to 8.3%. Finally, the globulin-related proteins were present in amounts ranging from 2.8 to 17.3%. They were less abundant in comparison with legumin and vicilin, but they showed the largest relative variation of the four globulin classes. Correlations between the different external characteristics and globulin composition were determined. Comparison with soybean showed that pea lines show more variety in the abundance of globulin proteins, enabling a wider range of food application.

Vicilin and convicilin are potential major allergens from pea

BACKGROUND

Allergic reactions to pea (Pisum sativum) ingestion are frequently associated with lentil allergy in the Spanish population. Vicilin have been described as a major lentil allergen.

OBJECTIVE

To identify the main IgE binding components from pea seeds and to study their potential cross-reactivity with lentil vicilin.

METHODS

A serum pool or individual sera from 18 patients with pea allergy were used to detect IgE binding proteins from pea seeds by immunodetection and immunoblot inhibition assays. Protein preparations enriched in pea vicilin were obtained by gel filtration chromatography followed by reverse-phase high-performance liquid chromatography (HPLC). IgE binding components were identified by means of N-terminal amino acid sequencing. Complete cDNAs encoding pea vicilin were isolated by PCR, using primers based on the amino acid sequence of the reactive proteins.

RESULTS

IgE immunodetection of crude pea extracts revealed that convicilin (63 kDa), as well as vicilin (44 kDa) and one of its proteolytic fragments (32 kDa), reacted with more than 50% of the individual sera tested. Additional proteolytic subunits of vicilin (36, 16 and 13 kDa) bound IgE from approximately 20% of the sera. The lentil vicilin allergen Len c 1 strongly inhibited the IgE binding to all components mentioned above. The characterization of cDNA clones encoding pea vicilin has allowed the deduction of its complete amino acid sequence (90% of sequence identity to Len c 1), as well as those of its reactive proteolytic processed subunits.

CONCLUSIONS

Vicilin and convicilin are potential major allergens from pea seeds. Furthermore, proteolytic fragments from vicilin are also relevant IgE binding pea components. All these proteins cross-react with the major lentil allergen Len c 1.

Characterization of pea vicilin. 2. Consequences of compositional heterogeneity on heat-induced gelation behavior

The gelling characteristics of two vicilin fractions from pea (Pisum sativum L.) were compared over a range of pH and salt conditions after preliminary results showed that despite having equal opportunity to unfold, and expose hydrophobic residues, they had different minimum gelling concentrations (at pH 7.6). Furthermore, at this pH one fraction formed turbid gels and the other formed transparent gels. The fraction that formed transparent gels contained a substantial amount of the 70 kDa alpha-subunits of vicilin, and thus it was hypothesized that the highly charged N-terminal extension region on these 70 kDa subunits hinders gelation of this vicilin fraction at pH 7.6 and I = 0.2 due to repulsion of the net negative charge. The experiments designed to test this hypothesis are presented and discussed in this paper and prove that the hypothesis was true, which offers the possibility to control or modify the gelation behavior of vicilin on the basis of information of its subunit composition.

Characterization of pea vicilin. 1. Denoting convicilin as the alpha-subunit of the Pisum vicilin family

Vicilin, a major globulin protein of pea that has been described as "extremely heterogeneous in terms of its polypeptide composition", was extracted from pea flour under alkaline conditions and subsequently fractionated by salt under acid conditions. This procedure induced the separation of vicilin into two fractions, which, after purification, were called vicilin 1 degrees and vicilin 2 degrees. Vicilin 2 degrees was seen on SDS-PAGE to contain the third globulin protein of pea, convicilin (a band at approximately 70 kDa). Vicilin fractions were thus characterized using gel electrophoresis, differential scanning calorimetry, circular dichroism, and pH-dependent solubility in order to determine whether the convicilin should in fact be considered as a third separate globulin protein of pea. On the basis of the results obtained it was concluded that this distinct polypeptide of the Pisum vicilin gene family should be further denoted as a subunit of the salt extractable protein vicilin. The definition of vicilin heterogeneity should therefore be extended to acknowledge the possible oligomeric inclusion of the 70 kDa polypeptide that is here denoted as the alpha-subunit.

8S globulin of mungbean [Vigna radiata (L.) Wilczek]: cloning and characterization of its cDNA isoforms, expression in Escherichia coli, purification, and crystallization of the major recombinant 8S isoform

Three isoforms of the cDNA of the major 8S globulin of mungbean, 8Salpha, 8Salpha', and 8Sbeta, were isolated, cloned, and characterized. The cDNA sequences of 8Salpha, 8Salpha', and 8Sbeta had open reading frames of 1362, 1359 or 1362, and 1359 bp, respectively, which code for 454, 453 or 454, and 453 amino acids corresponding to molecular weights of 51 973, 51 627 or 51 758, and 51 779, respectively. Homology in terms of cDNA and amino acid sequences was 91-92% between 8Salpha and 8Salpha', 87% between 8Salpha and 8Sbeta, and 86-88% between 8Salpha' and 8Sbeta. The signal peptide was found to be 1-25, 1-24 or 25, and 1-23 for 8Salpha, 8Salpha', and 8Sbeta, respectively, using the signalP website (Nielsen, H.; Engelbrecht, J.; Brunak, S.; von Heijne, G. Protein Eng. 1997, 10, 1-6). The propeptide was determined to be IVHREN. A single site for glycosylation (N-X-S/T) was observed about 90 amino acids from the C terminus. Homology between mungbean 8S isoforms and other 7-8S proteins ranged from 45 to 68% within members of the legume family and 29 to 34% for crops of different species. The major isoform 8Salpha was expressed in Escherichia coli and purified by successive ammonium sulfate fractionation, hydrophobic interaction, and Mono Q column chromatography. The recombinant 8Salpha, but not the native form, was successfully crystallized producing rhombohedral crystals.

Dry bean protein functionality

Dry beans are an important source of proteins, carbohydrates, dietary fiber, and certain minerals and vitamins in the human food supply. Among dry beans, Phaseolus beans are cultivated and consumed in the greatest quantity on a worldwide basis. Typically, most dry beans contain 15 to 25% protein on a dry weight basis (dwb). Water-soluble albumins and salt-soluble globulins, respectively, account for up to 10 to 30% and 45 to 70% of the total proteins (dwb). Dry bean albumins are typically composed of several different proteins, including lectins and enzyme inhibitors. A single 7S globulin dominates dry bean salt soluble fraction (globulins) and may account for up to 50 to 55% of the total proteins in the dry beans (dwb). Most dry bean proteins are deficient in sulfur amino acids, methionine, and cysteine, and therefore are of lower nutritional quality when compared with the animal proteins. Despite this limitation, dry beans make a significant contribution to the human dietary protein intake. In bean-based foods, dry bean proteins also serve additional functions that may include surface activity, hydration, and hydration-related properties, structure, and certain organoleptic properties. This article is intended to provide an overview of dry bean protein functionality with emphases on nutritional quality and hydration-related properties.

Structure and characterization of the gene encoding alpha subunit of soybean beta-conglycinin

beta-conglycinin, a soybean seed storage protein, is comprised of three different subunits, a, alpha', and beta. Several candidates for the alpha subunit gene have been isolated, however, the structure of the alpha subunit gene has not been completely determined. Accordingly, it was also unknown which of the gene candidates are functionally active. Here, we have determined the nucleotide sequence and transcription start site of the alpha subunit gene, and compared the structural components with those of the other subunits or other seed protein genes. The a subunit gene, which is located on a 7.6-kb EcoRI fragment, was composed of six exons that had the same organization as those for the alpha' subunit gene. Within a 400 bp upstream region of the transcription start site, four regions (designated as boxes I, II, III, and IV) were found to be conserved among the alpha, alpha', and other seed protein genes. Genomic Southern blot analysis of soybean varieties lacking the alpha subunit gene candidate indicated that the gene characterized in this paper actually encodes the a subunit and is functionally active. In addition, these experiments revealed the presence of an additional gene which is also responsible for the expression of the a subunit.

Differentially regulated inhibitor-sensitive and insensitive protease genes from the phytophagous insect pest, Helicoverpa armigera, are members of complex multigene families

Ingestion of soybean Kunitz trypsin inhibitor (SKTI) by larvae of the phytophagous insect pest Helicoverpa armigera induced production of inhibitor-insensitive protease activity. The induced activity was not due to proteolytic enzymes of different mechanistic classes, but rather to variants of the existing enzymes. Characterization of cDNAs showed that sequences encoding proteins of the serine protease family were abundant in gut tissue of both control and SKTI-fed insects. The majority of serine protease family cDNAs encode enzymes closely homologous to trypsin and chymotrypsin; comparison of these sequences shows variation in amino acid residues within the region which would be in contact with a protein protease inhibitor. More diverged sequences which may not encode active proteases are also present. All the cDNAs examined were found to derive from multigene families; at least 28 different genes are present in the serine protease family. Chronic ingestion of SKTI results in some serine protease-encoding mRNA species increasing in level, whereas others decrease. Chymotrypsin-encoding mRNAs tend to increase in level as a result of SKTI ingestion, but no clear trend is shown by trypsin-encoding mRNAs. It is suggested that multiple, varying protease-encoding genes are an adaptive mechanism for reducing the deleterious effects of plant protease inhibitors.

Promoter analysis of seed storage protein genes from Canavalia gladiata D.C

A number of A/T-rich sequences and a CATGCAT/A sequence are contained in the 5'-upstream regions of the genes encoding concanavalin A (Con A) and canavalin, two major seed storage proteins of Canavalia gladiata D.C. To study the role of these sequences in the seed-specific gene expression, we constructed 5'-deletion mutants and examined the transient expression of beta-glucuronidase reporter gene by particle bombardment and the stable expression by Agrobacterium-mediated transformation of tobacco plants. Positive regulatory elements were located in the -894/-602 and -602/-74 regions of the Con A gene, and in the -428/-376, -281/-155 and -155/-50 regions of the canavalin gene. In addition, the results suggested that the A/T-rich sequences in the 5'-upstream region of the Con A gene play a role in transcriptional activation, but that those of the canavalin gene have little effect on the gene expression. The CATGCAT/A sequence was not sufficient by itself for high levels of expression of both the Con A and canavalin genes. The canavalin polypeptide amounted to about 1% of the total extractable protein in the transgenic tobacco seeds, but the Con A polypeptide was not detected in the extractable protein.

The legumin gene family: a reconstructed Vicia faba legumin gene encoding a high-molecular-weight subunit is related to type B genes

Nucleotide sequence information from a partial genomic clone, a cDNA clone, a RACE clone and a PCR fragment was combined to reconstruct the first reported complete gene sequence encoding a large legumin subunit, designated LelB3. The length difference to the well-characterized major legumin subunits is caused by an extended glutamine/glutamic acid-rich region encoded by the C-terminal part of the alpha chain. Amino acid sequence comparisons reveal that gene LelB3 is more closely related to B-type than to A-type legumin genes of Vicia faba. Gene LelB3 is a member of a small gene family as indicated by published (Pich and Schubert, Biol Zbl 112 (1993); 342-350) and limited own data.

Characterization of a soybean beta-conglycinin-degrading protease cleavage site

Protease C1, an enzyme from soybean (Glycine max [L.] Merrill cv Amsoy 71) seedling cotyledons, was previously determined to be the enzyme responsible for the initial degradation of the alpha' and alpha subunits, but not the beta subunit, of beta-conglycinin storage protein. The sizes of the proteolytic products generated by the action of protease C1 suggest that the cleavage sites on the alpha' and alpha subunits of beta-conglycinin may be located in their N-terminal domain, which is not found in the beta subunit of beta-conglycinin. To check this hypothesis, storage proteins from other plant species that are homologous to either the alpha'/alpha or the beta subunit of beta-conglycinin were tested as substrates. As expected, the convicilin from pea (Pisum sativum), a protein homologous to the alpha' and alpha subunits of beta-conglycinin, was digested by protease C1. The vicilins from pea as well as vicilins from adzuki bean (Vigna angularis), garden bean (Phaseolus vulgaris), black-eyed pea (Vigna unguiculata), and mung bean (Vigna radiata), storage proteins that are homologous to the beta subunit of soybean beta-conglycinin, were not degraded by protease C1. Degradation of soybean beta-conglycinin involves a sequential attack of the alpha subunit at multiple sites, culminating in the formation of a stable intermediate of 53.5 kD and a final product of 48.0 kD. The cleavage sites resulting in this formation of the intermediates and final product were determined by N-terminal analysis. These were compared to the known amino acid sequences of the three beta-conglycinin subunits. Results showed these two polypeptides to be generated by proteolysis of the alpha subunit at regions bearing long strings of acidic amino acid residues.

Cloning and sequencing of a cDNA encoding the major storage proteins of Theobroma cacao : Identification of the proteins as members of the vicilin class of storage proteins

The major storage proteins, polypeptides of 31 and 47 kilodaltons (kDa), from the seeds of cocoa (Theobroma cacao L.), have been identified and partially purified by preparative gel electrophoresis. The polypeptides were both N-terminally blocked, but some N-terminal amino-acid sequence was obtained from a cyanogen bromide peptide common to both polypeptides, permitting the construction of an oligonucleotide probe. This probe was used to isolate the corresponding copy-DNA (cDNA) clone from a library made from poly(A)(+) RNA from immature cocoa beans. The cDNA sequence has a single major open reading frame, that translates to give a 566-amino-acid polypeptide of Mr 65 612. The existence of a common precursor to the 31- and 47-kDa polypeptides of this size was confirmed by immunoprecipitation from total poly(A)(+)RNA translation products. The precursor has an N-terminal hydrophobic sequence which appears to be a typical signal sequence, with a predicted site of cleavage 20 amino acids after the start. This is followed by a very hydrophilic domain of ∼ 110 amino acids, which, by analogy with the cottonseed α-globulin, is presumed to be cleaved off to leave a domain of approx. 47 kDa, very close to the observed size of the mature polypeptide. Like the hydrophilic domain of the cottonseed α-globulin the cocoa hydrophilic domain is very rich in glutamine and charged residues (especially glutamate), and contains several Cys-X-X-X-Cys motifs. The cyanogen-bromide peptide common to the 47-kDa and 31-kDa polypeptides is very close to the proposed start of the mature domain, indicating that the 31-kDa polypeptide arises via further C-terminal processing. The polypeptide sequence is homologous to sequences of the vicilin class of storage proteins, previously found only in legumes and cotton. Most of these proteins have a mature polypeptide size of approx. 47 kDa, and are synthesised as precursors only slightly larger than this. Some, however, are larger polypeptides (e.g. α-conglycinin from soybean is 72 kDa), usually due to an additional N-terminal domain. In cottonseed the situation appears to parallel that in cocoa in that the vicilin is synthesised as an approx. 70-kDa precursor and then processed to a 47-kDa (and in the case of cocoa also a 31-kDa) mature protein. In this context it is interesting that cotton is closer in evolutionary terms to cocoa than are the legumes, both cotton and cocoa being in the order Malvales.

Conserved amino acid sequences among plant proteins sorted to protein bodies and plant vacuoles. Can they play a role in protein sorting?

Amino acid sequence comparisons were made between the soybean alpha subunit of beta-conglycinin and 34 members of different plant protein families targeted to seed protein bodies or vacuoles. A number of short conserved amino acid sequences were identified in seed storage proteins, plant protease inhibitors and lectins, and the probable functions of these sequences are discussed. For proteins of known tertiary structure, these sequences map to the surface of the respective molecules. It is postulated that these regions produce a common secondary structure which could interact with other molecules involved in the sorting process. One of these regions, region A, is similar to the yeast carboxypeptidase Y (CPY) vacuolar targeting signal, and is present in both storage proteins and lectins. Computer modeling based upon the tertiary structure of concanavalin A (ConA) was used to generate models representing the structure of two highly related lectins from Dolichos biflorus, one of which is targeted to protein bodies and the other secreted. A different glycosylation pattern together with amino acid sequences upstream of the identified conserved amino acid sequences are predicted to modulate the presentation of the sorting domains in the lectins and be the determinant in the sorting of these lectins.

Interaction of seed nuclear proteins with transcriptionally-enhancing regions of the pea (Pisum sativum L.) legA gene promoter

An 873-basepairs promoter fragment (-833 to +40), of the legA (legumin seed storage protein) gene of pea is known to be fully functional in transgenic plants. This fragment has been enzymically cleaved, and the products examined for the ability to interact specifically with nuclear proteins. Use of DNA-binding and mobility-shift assays has shown that promoter sequences between -316 and +40 do not form stable complexes with seed nuclear extracts. Fragments from -549 to -316 and -833 to -582, however, did interact strongly with seed, but not leaf, nuclear proteins. Each probe reacted similarly to form three distinct and stable complexes, although only the complex with least mobility appeared to be specific when challenged with competitor DNA fragments. Competitor studies also indicate that a single factor (designated LABF1) forms these specific low-mobility complexes with both probes. Fractionation of seed nuclear proteins by sodium dodecyl sulphate polyacrylamide gel electrophoresis, followed by elution and renaturation, shows that LABF1 activity resides in the 84 000- to 116 000-Mr size range of polypeptides. The tissue-specific activity of LABF1 is temporally correlated with legumin gene expression, a relationship consistent with suggestions that this factor may act as a transcriptional enhancer.

Another class of vicilin gene in Pisum

We describe a novel class of vicilin gene in Pisum corresponding to a precursor polypeptide of Mr 68000. The mRNA corresponding to this polypeptide accumulates during seed development in a pattern similar to that of convicilin. Hybridization and sequence analyses show that this vicilin gene class is less homologous to other Pisum vicilin gene classes than these last are to each other. Gene-copy-number estimates and decreased stringency hybridizations of the gene class described here show that the Pisum vicilin gene family is bigger and more complex than hitherto reported.

The effect of different alleles at the r locus on the synthesis of seed storage proteins in Pisum sativum

Rocket immunoelectrophoresis was used to measure the accumulation of storage proteins in developing cotyledons of two Pisum sativum (pea) genotypes, that were close to isogenic except for the nature of the allele at the r locus. There was a marked decrease in legumin accumulation in the rr (wrinkled-seeded) genotype compared to the RR (round-seeded) genotype. The accumulation of vicilin did not differ greatly between the two genotypes. Pulse-labelling studies indicated that the differences in rates of accumulation of legumin between the rr and RR genotypes were a consequence of differences in rates of protein synthesis. Measurements of relative amounts of specific mRNAs, using cDNA clones as probes, showed lower amounts of legumin mRNA in developing cotyledons of the rr, compared to the RR, genotype. Both vicilin mRNAs and convicilin mRNA, the latter of which shows a similar temporal pattern of expression to those of the major legumin species, are relatively unaffected by the nature of the allele at the r locus. Nuclear run-on transcription experiments indicated no differences in the rate of synthesis of legumin transcripts in the rr and RR near-isolines. The consequences of homozygosity for the r allele on storage protein mRNA levels in vitro may be mimicked by manipulating the sucrose concentration of the culture medium.

Pea convicilin: structure and primary sequence of the protein and expression of a gene in the seeds of transgenic tobacco

Convicilin, a trimeric globulin of pea (Pisum sativum L.) seeds, is closely related to vicilin and composed of polypeptides of 68.2 kilodaltons. A partial copy DNA (cDNA) clone encoding convicilin was isolated, sequenced, and used to select a convicilin gene from a pea genomic library. A part of the genomic clone was sequenced to obtain the coding sequences missing in the cDNA clone and a further 1 kilobase 5' to the start of transcription were also obtained. The entire sequence of convicilin was deduced from the combined genomic and cDNA sequences. The complete gene encoding convicilin was transferred to tobacco (Nicotiana tabacum L.) and the characteristics of its expression in the seeds of transgenic plants were studied. An unprocessed polypeptide, which was found only in the seeds of the transgenic plants, was identical in size to pea convicilin, and was recognized by vicilin antibodies. Convicilin, which does not undergo posttranslational cleavage in peas, was partially processed to polypeptides of a relative molecular mass (Mr) of approx. 50000 in transgenic tobacco seeds. There was a twofold variation in the level of convicilin accumulated by the mature seeds of a number of transgenic plants and this was well correlated with the number of gene copies incorporated in the different transformants. In the seeds of tobacco plants that contained a single copy of the transferred gene it was estimated that convicilin comprised up to 2% of the seed protein. Thus, using a combination of gene sequencing and expression in a heterologous host we believe we have characterized the gene corresponding to theCvc locus, whereas the gene described by D. Bown et al. (1988, Biochem J.,251, 717-726) probably encodes a minor convicilin-related protein.

Transcriptional and posttranscriptional regulation of seed storage-protein gene expression in pea (Pisum sativum L.)

At least three classes of legumin, encoded by the gene families legA, legJ and legS, and a lectin, encoded by a single gene, accumulate in the developing cotyledons of Pisum sativum L. Transcription rates for the genes encoding these proteins were measured in nuclei isolated from cotyledons at 12 and 16 days after flowering (DAF). The steady-state levels of the corresponding mRNA species were also measured in absolute terms throughout cotyledon development, from 8-9 to 28 DAF. When transcription rates and steady-state mRNA levels of the different gene families are compared, there is little correlation. This indicates a posttranscriptional regulation of the level of expression of these storage proteins in the developing cotyledons. Expression of the legumin genes is known to be seed-specific, whereas expression of the lectin gene is found in both seed and root. When transcription rates were measured in leaf nuclei the levels of legumin and lectin transcripts detected approached background levels, indicating that these genes are either inactive or transcribed at very low levels in leaves; however, the rate of transcription of the chlorophyll a/b-binding protein gene was high. This points to transcriptional control as the major factor in the organ-specificity of legumin and lectin expression.

The 5' splice site: phylogenetic evolution and variable geometry of association with U1RNA

The 5' splice site sequences of 3294 introns from various organisms (1-672) were analyzed in order to determine the rules governing evolution of this sequence, which may shed light on the mechanism of cleavage at the exon-intron junction. The data indicate that, currently, in all organisms, a common sequence 1GUAAG6U and its derivatives are used as well as an additional sequence and its derivatives, which differ in metazoa (G/1GUgAG6U), lower eucaryotes (1GUAxG6U) and higher plants (AG/1GU3A). They all partly resemble the prototype sequence AG/1GUAAG6U whose 8 contigous nucleotides are complementary to the nucleotides 4-11 of U1RNA, which are perfectly conserved in the course of phylogenetic evolution. Detailed examination of the data shows that U1RNA can recognize different parts of 5' splice sites. As a rule, either prototype nucleotides at position -2 and -1 or at positions 4, 5 or 6 or at positions 3-4 are dispensable provided that the stability of the U1RNA-5' splice site hybrid is conserved. On the basis of frequency of sequences, the optimal size of the hybridizable region is 5-7 nucleotides. Thus, the cleavage at the exon-intron junction seems to imply, first, that the 5' splice site is recognized by U1RNA according to a "variable geometry" program; second, that the precise cleavage site is determined by the conserved sequence of U1RNA since it occurs exactly opposite to the junction between nucleotides C9 and C10 of U1RNA. The variable geometry of the U1RNA-5' splice site association provides flexibility to the system and allows diversification in the course of phylogenetic evolution.