Inhibitory serpins from wheat grain with reactive centers resembling glutamine-rich repeats of prolamin storage proteins. Cloning and characterization of five major molecular forms

Cell-type proteomic and metabolomic resolution of early and late grain filling stages of wheat endosperm

The nutritional value of wheat grains, particularly their protein and metabolite composition, is a result of the grain-filling process, especially in the endosperm. Here, we employ laser microdissection (LMD) combined with shotgun proteomics and metabolomics to generate a cell type-specific proteome and metabolome inventory of developing wheat endosperm at the early (15 DAA) and late (26 DAA) grain-filling stages. We identified 1803 proteins and 41 metabolites from four different cell types (aleurone (AL), sub-aleurone (SA), starchy endosperm (SE) and endosperm transfer cells (ETCs). Differentially expressed proteins were detected, 67 in the AL, 31 in the SA, 27 in the SE and 50 in the ETCs between these two-time points. Cell-type accumulation of specific SUT and GLUT transporters, sucrose converting and starch biosynthesis enzymes correlate well with the respective sugar metabolites, suggesting sugar upload and starch accumulation via nucellar projection and ETC at 15 DAA in contrast to the later stage at 26 DAA. Changes in various protein levels between AL, SA and ETC support this metabolic switch from 15 to 26 DAA. The distinct spatial and temporal abundances of proteins and metabolites revealed a contrasting activity of nitrogen assimilation pathways, e.g. for GOGAT, GDH and glutamic acid, in the different cell types from 15 to 26 DAA, which can be correlated with specific protein accumulation in the endosperm. The integration of cell-type specific proteome and metabolome data revealed a complex metabolic interplay of the different cell types and a functional switch during grain development and grain-filling processes.

TcSERPIN, an inhibitor that interacts with cocoa defense proteins and has biotechnological potential against human pathogens

In plants, serpins are a superfamily of serine and cysteine protease inhibitors involved in stress and defense mechanisms, with potential for controlling agricultural pests, making them important biotechnological tools. The objective of this study was to characterize a serpin from Theobroma cacao, called TcSERPIN, to identify its endogenous targets and determine its function and biotechnological potential. TcSERPIN has 390 amino acid residues and shows conservation of the main active site, RCL. Cis-elements related to light, stress, hormones, anaerobic induction, cell cycle regulation and defense have been identified in the gene's regulatory region. TcSERPIN transcripts are accumulated in different tissues of Theobroma cacao. Furthermore, in plants infected with Moniliophtora perniciosa and Phytophthora palmivora, the expression of TcSERPIN was positively regulated. The protein spectrum, rTcSERPIN, reveals a typical β-sheet pattern and is thermostable at pH 8, but loses its structure with temperature increases above 66°C at pH 7. At the molar ratios of 0.65 and 0.49, rTcSERPIN inhibited 55 and 28% of the activity of papain from Carica papaya and trypsin from Sus scrofa, respectively. The protease trap containing immobilized rTcSERPIN captured endogenous defense proteins from cocoa extracts that are related to metabolic pathways, stress and defense. The evaluation of the biotechnological potential against geohelminth larvae showed that rTcSERPIN and rTcCYS4 (Theobroma cacao cystatin 4) reduced the movement of larvae after 24 hours. The results of this work show that TcSERPIN has ideal biochemical characteristics for biotechnological applications, as well as potential for studies of resistance to phytopathogens of agricultural crops.

Plant Serpins: Potential Inhibitors of Serine and Cysteine Proteases with Multiple Functions

Plant serpins are a superfamily of protein inhibitors that have been continuously studied in different species and have great biotechnological potential. However, despite ongoing studies with these inhibitors, the biological role of this family in the plant kingdom has not yet been fully clarified. In order to obtain new insights into the potential of plant serpins, this study presents the first systematic review of the topic, whose main objective was to scrutinize the published literature to increase knowledge about this superfamily. Using keywords and the eligibility criteria defined in the protocol, we selected studies from the Scopus, PubMed, and Web of Science databases. According to the eligible studies, serpins inhibit different serine and non-serine proteases from plants, animals, and pathogens, and their expression is affected by biotic and abiotic stresses. Moreover, serpins like AtSerpin1, OSP-LRS, MtSer6, AtSRP4, AtSRP5, and MtPiI4, act in resistance and are involved in stress-induced cell death in the plant. Also, the system biology analysis demonstrates that serpins are related to proteolysis control, cell regulation, pollen development, catabolism, and protein dephosphorylation. The information systematized here contributes to the design of new studies of plant serpins, especially those aimed at exploring their biotechnological potential.

Proteomic Characterization of Wheat Protein Fractions Taken at Different Baking Conditions

Food processing conditions affect the structure, solubility, and therefore accurate detection of gluten proteins. We investigated the influence of dough, bread, and pretzel making on the composition of different wheat protein fractions obtained by Osborne fractionation. The albumin/globulin, gliadin, and glutenin fractions from flour, dough, crispbread, bread, and pretzel were analyzed using RP-HPLC, SDS-PAGE, and untargeted nanoLC-MS/MS. This approach enabled an in-depth profiling of the fractionated proteomes and related compositional changes to processing conditions (mixing, heat, and alkali treatment). Overall, heat treatment demonstrated the most pronounced effect. Label-free quantitation revealed significant changes in the relative abundances of 82 proteins within the fractions of bread crumb and crust in comparison to flour. Certain gluten proteins showed shifts or reductions in particular fractions, indicating their incorporation into the gluten network through SS and non-SS cross-links. Other gluten proteins were enriched, suggesting their limited involvement in the gluten network formation.

Genes Encoding Structurally Conserved Serpins in the Wheat Genome: Identification and Expression Profiles during Plant Development and Abiotic and Biotic Stress

Serpins constitute a family of proteins with a very wide distribution in nature. Serpins have a well-conserved tertiary structure enabling irreversible protease inhibition or other specific biochemical functions. We examined the 189 putative wheat serpin genes previously identified by Benbow et al. (2019) via analysis of gene annotations (RefSeq v1.0) and combined our previous examinations of wheat ESTs and the 454 genome assembly. We found that 81 of the 189 putative serpin genes, plus two manually annotated genes, encode full-length, structurally conserved serpins. Expression of these serpin genes during wheat development and disease/abiotic stress responses was analysed using a publicly available RNAseq database. Results showed that the wheat LR serpins, homologous to Arabidopsis AtSerpin1 and barley BSZx, are ubiquitously expressed across all tissues throughout the wheat lifecycle, whereas the expression of other wheat serpin genes is tissue-specific, including expression only in the grain, only in the root, and only in the anther and microspore. Nine serpin genes were upregulated in both biotic and abiotic responses. Two genes in particular were highly expressed during disease and abiotic challenges. Our findings provide valuable information for further functional study of the wheat serpins, which in turn may lead to their application as molecular markers in wheat breeding.

2D-DIGE based proteome analysis of wheat-Thinopyrum intermedium 7XL/7DS translocation line under drought stress

Background

Drought stress is the most limiting factor for plant growth and crop production worldwide. As a major cereal crop, wheat is susceptible to drought. Thus, discovering and utilizing drought-tolerant gene resources from related species are highly important for improving wheat drought resistance. In this study, the drought tolerance of wheat Zhongmai 8601-Thinopyrum intermedium 7XL/7DS translocation line YW642 was estimated under drought stress, and then two-dimensional difference gel electrophoresis (2D-DIGE) based proteome analysis of the developing grains was performed to uncover the drought-resistant proteins.

Results

The results showed that 7XL/7DS translocation possessed a better drought-tolerance compared to Zhongmai 8601. 2D-DIGE identified 146 differential accumulation protein (DAP) spots corresponding to 113 unique proteins during five grain developmental stages of YW642 under drought stress. Among them, 55 DAP spots corresponding to 48 unique proteins displayed an upregulated expression, which were mainly involved in stress/defense, energy metabolism, starch metabolism, protein metabolism/folding and transport. The cis-acting element analysis revealed that abundant stress-related elements were present in the promoter regions of the drought-responsive protein genes, which could play important roles in drought defense. RNA-seq and RT-qPCR analyses revealed that some regulated DAP genes also showed a high expression level in response to drought stress.

Conclusions

Our results indicated that Wheat-Th. intermedium 7XL/7DS translocation line carried abundant drought-resistant proteins that had potential application values for wheat drought tolerance improvement.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08599-1.

In-Depth Proteomic Analysis of the Secondary Dormancy Induction by Hypoxia or High Temperature in Barley Grains

In barley, incubation of primary dormant (D1) grains on water under conditions that do not allow germination, i.e. 30°C in air and 15°C or 30°C in 5% O2, induces a secondary dormancy (D2) expressed as a loss of the ability to germinate at 15°C in air. The aim of this study was to compare the proteome of barley embryos isolated from D1 grains and D2 ones after induction of D2 at 30°C or in hypoxia at 15°C or 30°C. Total soluble proteins were analyzed by 2DE gel-based proteomics, allowing the selection of 130 differentially accumulated proteins (DAPs) among 1,575 detected spots. According to the protein abundance profiles, the DAPs were grouped into six abundance-based similarity clusters. Induction of D2 is mainly characterized by a down-accumulation of proteins belonging to cluster 3 (storage proteins, proteases, alpha-amylase inhibitors and histone deacetylase HD2) and an up-accumulation of proteins belonging to cluster 4 (1-Cys peroxiredoxin, lipoxygenase2 and caleosin). The correlation-based network analysis for each cluster highlighted central protein hub. In addition, most of genes encoding DAPs display high co-expression degree with 19 transcription factors. Finally, this work points out that similar molecular events accompany the modulation of dormancy cycling by both temperature and oxygen, including post-translational, transcriptional and epigenetic regulation.

Intestinal Exposure to Food-Derived Protease Inhibitors: Digestion Physiology- and Gut Health-Related Effects

Plant-derived protease inhibitors (PI), such as Bowman-Birk inhibitors and Kunitz-type inhibitors, have been suggested to negatively affect dietary protein digestion by blocking the activity of trypsin and chymotrypsin in the human gastrointestinal system. In addition, some PIs may possess proinflammatory activities. However, there is also scientific evidence on some beneficial effects of PIs, for example, gut-related anti-inflammatory and chemopreventive activities in vitro and in vivo. Some PIs are sensitive to processing and digestion; thus, their survival is an important aspect when considering their positive and negative bioactivities. The aim of this review was to evaluate the relevance of PIs in protein digestion in humans and to discuss the potential of PIs from whole foods and as purified compounds in decreasing symptoms of bowel-related conditions. Based on the reviewed literature, we concluded that while the complex interactions affecting plant protein digestibility and bioavailability remain unclear, PI supplements could be considered for targeted purposes to mitigate inflammation and gastric pain.

Increased Wheat Protein Content via Introgression of an HMW Glutenin Selectively Reshapes the Grain Proteome

Introgression of a high-molecular-weight glutenin subunit (HMW-GS) allele, 1Ay21∗, into commercial wheat cultivars increased overall grain protein content and bread-making quality, but the role of proteins beyond this HMW-GS itself was unknown. In addition to increased abundance of 1Ay HMW-GS, 115 differentially accumulated proteins (DAPs) were discovered between three cultivars and corresponding introgressed near-isogenic lines. Functional category analysis showed that the DAPs were predominantly other storage proteins and proteins involved in protein synthesis, protein folding, protein degradation, stress response, and grain development. Nearly half the genes encoding the DAPs showed strong coexpression patterns during grain development. Promoters of these genes are enriched in elements associated with transcription initiation and light response, indicating a potential connection between these cis-elements and grain protein accumulation. A model of how this HMW-GS enhances the abundance of machinery for protein synthesis and maturation during grain filling is proposed. This analysis not only provides insights into how introgression of the 1Ay21∗ improves grain protein content but also directs selection of protein candidates for future wheat quality breeding programs.

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Ay HMW-GS itself only contributes to 20% of the significant GPC increase in Ay NILs.

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Ay HMW-GS enhances other storage protein and protein synthesis machinery abundances.

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Expression of genes encoding Ay HMW-GS–induced proteins are strongly coexpressed.

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It provides a mechanistic model to influence future wheat quality breeding programs.

ApSerpin-ZX from Agapanthus praecox, is a potential cryoprotective agent to plant cryopreservation

Cryopreservation-induced cell death is regarded as an important problem faced by cryobiologists. Oxidative stress and programmed cell death are detrimental to cell survival. Serine protease inhibitors (serpins) inhibit pro-cell-death proteases and play a pro-survival role in excessive cell death induced by abiotic stress. In this study, ApSerpin-ZX was isolated from Agapanthus praecox and characterized as a protective protein in plant cryopreservation. The mRNA level of ApSerpin-ZX was elevated under abiotic stress, such as salt, osmosis, oxidative, cold, and cryoinjury. The purified recombinant protein expressed in E. coli was added to the plant vitrification solution and used for A. praecox embryogenic callus cryopreservation. The concentration of 0.6-4.8 mg∙L^-1 of ApSerpin-ZX protein was beneficial to the survival of cryopreserved embryogenic callus of A. praecox. The most effective concentration was 1.2 mg∙L^-1, which elevated the survival by 37.15%. Subsequently, the cryopreservation procedure with 1.2 mg∙L^-1 of ApSerpin-ZX protein was regarded as the treated group, compared to standard procedure, to determine the physiological mechanism of ApSerpin-ZX protein on cryopreserved cell. The MDA and H₂O₂ contents were significantly decreased in the treated group, along with reduced OH· generation activity in the recovery stage. After the addition of ApSerpin-ZX, the POD and CAT activities keep increased, while SOD activity increased only after dehydration. Besides, the caspase-1-like and caspase-3-like activities were lower than the standard procedure. This study indicated that ApSerpin-ZX was a potential cryoprotective agent that alleviated oxidative stress and cell death induced by cryopreservation.

Genome Wide Identification and Comparative Analysis of the Serpin Gene Family in Brachypodium and Barley

Serpins (serine protease inhibitors) constitute one of the largest and most widely distributed superfamilies of protease inhibitors and have been identified in nearly all organisms. To gain significant insights, a comprehensive in silico analysis of the serpin gene family was carried out in the model plant for temperate grasses Brachypodium distachyon and barley Hordeum vulgare using bioinformatic tools at the genome level for the first time. We identified a total of 27 BdSRPs and 25 HvSRP genes in Brachypodium and barley, respectively, showing an unexpectedly high gene number in these model plants. Gene structure, conserved motifs and phylogenetic comparisons of serpin genes supported the role of duplication events in the expansion and evolution of serpin gene family. Further, purifying selection pressure was found to be a main driving force in the evolution of serpin genes. Genome synteny analysis indicated that BdSRP genes were present in syntenic regions of barley, rice, sorghum and maize, suggesting that they evolved before the divergence of these species from common ancestor. The distinct expression pattern in specific tissues further suggested a specialization of functions during development and in plant defense. These results suggest that the LR serpins (serpins with Leu-Arg residues at P2-P1') identified here can be utilized as candidates for exploitation in disease resistance, pest control and preventing stress-induced cell death. Additionally, serpins were identified that could lead to further research aimed at validating and functionally characterizing the role of potential serpin genes from other plants.

Programmed cell death (PCD) control in plants: New insights from the Arabidopsis thaliana deathosome

Programmed cell death (PCD) is a genetically controlled process that leads to cell suicide in both eukaryotic and prokaryotic organisms. In plants PCD occurs during development, defence response and when exposed to adverse conditions. PCD acts controlling the number of cells by eliminating damaged, old, or unnecessary cells to maintain cellular homeostasis. Unlike in animals, the knowledge about PCD in plants is limited. The molecular network that controls plant PCD is poorly understood. Here we present a review of the current mechanisms involved with the genetic control of PCD in plants. We also present an updated version of the AtLSD1 deathosome, which was previously proposed as a network controlling HR-mediated cell death in Arabidopsis thaliana. Finally, we discuss the unclear points and open questions related to the AtLSD1 deathosome.

Characterising avenin-like proteins (ALPs) from albumin/globulin fraction of wheat grains by RP-HPLC, SDS-PAGE, and MS/MS peptides sequencing

BACKGROUND

Wheat grain avenin-like proteins (ALPs) belong to a recently discovered class of wheat grain storage protein. ALPs in wheat grains not only have beneficial effects on dough quality but also display antifungal activities, which is a novel observation for wheat storage proteins. Previous studies have shown that ALPs are likely present in the albumin/globulin fractions of total protein extract from wheat flour. However, the accumulation characteristics of these ALPs in the mature wheat grain remains unknown.

RESULTS

In the present study, a total of 13 ALPs homologs were isolated and characterized in the albumin/globulin fractions of the wheat protein extract. A combination of multiple techniques including RP-HPLC, SDS-PAGE, MALDI-TOF and peptide sequencing were used for accurate separation and identification of individual ALP homolog. The C-terminal TaALP-by-4AL/7DS, TaALP-by-4AL/7AS/7DS, TaALP-bx/4AL/7AS/7DS, TaALP-ay-7DS, TaALP-ay-4AL, TaALP-ax-4AL, TaALP-ax-7AS, and TaALP-ax-7DS, were separated as individual protein bands from wheat flour for the first time. These unique ALPs peptides were mapped to the latest wheat genome assembly in the IWGSC database. The characteristic defence related proteins present in albumin and globulin fractions, such as protein disulfide-isomerase (PDI), grain softness protein (GSP), alpha-amylase inhibitors (AAIs) and endogenous alpha-amylase/subtilisin inhibitor were also found to co-segregate with these identified ALPs, avenin-3 and α-gliadins. The molecular weight range and the electrophoresis segregation properties of ALPs were characterised in comparison with the proteins containing the tryp_alpha_amyl domain (PF00234) and the gliadin domain (PF13016), which play a role in plant immunity and grain quality. We examined the phylogenetic relationships of the AAIs, GSP, avenin-3, α-gliadins and ALPs, based on the alignment of their functional domains. MALDI-TOF profiling indicated the occurrence of certain post-translations modifications (PTMs) in some ALP subunits.

CONCLUSIONS

We reported for the first time the complete profiling of ALPs present in the albumin/globulin fractions of wheat grain protein extracts. We concluded that majority of the ALPs homologs are expressed in wheat grains. We found clear evidence of PTMs in several ALPs peptides. The identification of both gliadin domain (PF13016) and Tryp_alpha_amyl domain (PF00234) in the mature forms of ALPs highlighted the multiple functional properties of ALPs in grain quality and disease resistance.

Stimulatory Response of Celiac Disease Peripheral Blood Mononuclear Cells Induced by RNAi Wheat Lines Differing in Grain Protein Composition

Wheat gluten proteins are responsible for the bread-making properties of the dough but also for triggering important gastrointestinal disorders. Celiac disease (CD) affects approximately 1% of the population in Western countries. The only treatment available is the strict avoidance of gluten in the diet. Interference RNA (RNAi) is an excellent approach for the down-regulation of genes coding for immunogenic proteins related to celiac disease, providing an alternative for the development of cereals suitable for CD patients. In the present work, we report a comparative study of the stimulatory capacity of seven low-gluten RNAi lines differing in grain gluten and non-gluten protein composition, relevant for CD and other gluten pathologies. Peripheral blood mononuclear cells (PBMCs) of 35 patients with active CD were included in this study to assess the stimulatory response induced by protein extracts from the RNAi lines. Analysis of the proliferative response and interferon-gamma (INF-γ) release of PBMCs demonstrated impaired stimulation in response to all RNAi lines. The lower response was provided by lines with a very low content of α- and γ-gliadins, and low or almost devoid of DQ2.5 and p31-43 α-gliadin epitopes. The non-gluten protein seems not to play a key role in PBMC stimulation.

Peptide-based protease inhibitors from plants

Proteases have an important role in homeostasis, and dysregulation of protease function can lead to pathogenesis. Therefore, proteases are promising drug targets in cancer, inflammation, and neurodegenerative disease research. Although there are well-established pharmaceuticals on the market, drug development for proteases is challenging. This is often caused by the limited selectivity of currently available lead compounds. Proteinaceous plant protease inhibitors are a diverse family of (poly)peptides that are important to maintain physiological homeostasis and to serve the innate defense machinery of the plant. In this review, we provide an overview of the diversity of plant peptide- and protein-based protease inhibitors (PIs), provide examples of such compounds that target human proteases, and discuss opportunities for these molecules in protease drug discovery and development.

Serpins: Genome-Wide Characterisation and Expression Analysis of the Serine Protease Inhibitor Family in Triticum aestivum

The serine protease inhibitor (serpin) gene family is the largest family of protease inhibitors. Serine protease inhibitors have an active, but under-characterized, role in grain development and defense against pathogen attack in cereal crops. By exploiting publicly available genomic, transcriptomic and proteomic data for wheat (Triticum aestivum), we have identified and annotated the entire ’serpinome’ of wheat and constructed a high-quality and robust phylogenetic tree of the gene family, identifying paralogous and homeologous clades from the hexaploid wheat genome, including the Serpin-Z group that have been well characterized in barley. Using publicly available RNAseq data (http://www.wheat-expression.com/), expression profiles of the wheat serpins were explored across a variety of tissues from the developing grain, spikelet and spike. We show that the SERPIN-Z clade, among others, are highly expressed during grain development, and that there is homeologous and paralogous functional redundancy in this gene family. Further to their role in grain development, serpins play an important but under-explored role in response to fungal pathogens. Using 13 RNAseq datasets of wheat tissues infected by fungal pathogens, we identified 37 serpins with a significant disease response. The majority of the disease-responsive serpins were upregulated by Fusarium graminearum, a destructive fungal pathogen that attacks the spike and developing grain of wheat. As serpins are ubiquitous in wheat grain, the genes encoding serpins may be linked to grain development, with their disease response a result of pleiotropy.

Plant serpin protease inhibitors: specificity and duality of function

The serpins are a family of structurally conserved protease inhibitors found in all animal and plant kingdoms. After interaction with their cognate substrate(s), their native energetically stressed state is relaxed by hydrolysis, resulting in a semi-stable covalent bond that disables the protease. The inherent flexible serpin structure supports additional non-inhibitory functions. This review will focus on several biological functions attributed to plant serpins, ranging from specific cell death protease inhibitors to a stabilizing role for β-amylase in seeds. Functional conservation of a particular serpin type, the LR serpins, is suggested by its compelling ubiquity throughout the plant kingdom. The multiple target specificity of plant serpins including the LR serpins enables them to perform dual functions that are not mutually exclusive both as a regulator of cell death and as a protective anti-pathogenic protein.

Quantitative analysis of the grain amyloplast proteome reveals differences in metabolism between two wheat cultivars at two stages of grain development

Background

Wheat (Triticum aestivum L.) is one of the world’s most important grain crops. The amyloplast, a specialized organelle, is the major site for starch synthesis and storage in wheat grain. Understanding the metabolism in amyloplast during grain development in wheat cultivars with different quality traits will provide useful information for potential yield and quality improvement.

Results

Two wheat cultivars, ZM366 and YM49–198 that differ in kernel hardness and starch characteristics, were used to examine the metabolic changes in amyloplasts at 10 and 15 days after anthesis (DAA) using label-free-based proteome analysis. We identified 523 differentially expressed proteins (DEPs) between 10 DAA and 15 DAA, and 229 DEPs between ZM366 and YM49–198. These DEPs mainly participate in eight biochemical processes: carbohydrate metabolism, nitrogen metabolism, stress/defense, transport, energetics-related, signal transduction, protein synthesis/assembly/degradation, and nucleic acid-related processes. Among these proteins, the DEPs showing higher expression levels at 10 DAA are mainly involved in carbohydrate metabolism, stress/defense, and nucleic acid related processes, whereas DEPs with higher expression levels at 15 DAA are mainly carbohydrate metabolism, energetics-related, and transport-related proteins. Among the DEPs between the two cultivars, ZM366 had more up-regulated proteins than YM49–198, and these are mainly involved in carbohydrate metabolism, nucleic acid-related processes, and transport.

Conclusions

The results of our study indicate that wheat grain amyloplast has the broad metabolic capability. The DEPs involved in carbohydrate metabolism, nucleic acids, stress/defense, and transport processes, with grain development and cultivar differences, are possibly responsible for different grain characteristics, especially with respect to yield and quality-related traits.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5174-z) contains supplementary material, which is available to authorized users.

Thermo-reversible inhibition makes aqualysin 1 from Thermus aquaticus a potent tool for studying the contribution of the wheat gluten network to the crumb texture of fresh bread

The thermo-active serine peptidase aqualysin 1 (Aq1) of Thermus aquaticus was applied in bread making to study the relative contribution of thermoset gluten to bread crumb texture. Aq1 is active between 30 °C and 90 °C with an optimum activity temperature of around 65 °C. It is inhibited by wheat endogenous serine peptidase inhibitors during dough mixing and fermentation and starts hydrolyzing gluten proteins during baking above 80 °C when the enzyme is no longer inhibited and most of the starch is gelatinized and contributes to structure formation. Aq1 activity reduced the molecular weight of gluten proteins and significantly increased their extractability in sodium dodecyl sulfate containing medium. While it had no impact on the specific bread volume and only limited impact on hardness, cohesiveness, springiness, resilience and chewiness, it impacted bread crumb coherence. We conclude that starch has a greater impact on crumb texture than thermoset gluten.

Noncanonical interactions between serpin and β-amylase in barley grain improve β-amylase activity in vitro

Serpin protease inhibitors and β-amylase starch hydrolases are very abundant seed proteins in the endosperm of grasses. β-amylase is a crucial enzyme in the beer industry providing maltose for fermenting yeast. In animals and plants, inhibitory serpins form covalent linkages that inactivate their cognate proteases. Additionally, in animals, noninhibitory functions for serpins are observed such as metabolite carriers and chaperones. The function of serpins in seeds has yet to be unveiled. In developing endosperm, serpin Z4 and β-amylase showed similar in vivo spatio-temporal accumulation properties and colocalize in the cytosol of transformed tobacco leaves. A molecular interaction between recombinant proteins of serpin Z4 and β-amylase was revealed by surface plasmon resonance and microscale thermophoresis yielding a dissociation constant of 10-7 M. Importantly, the addition of serpin Z4 significantly changes β-amylase enzymatic properties by increasing its maximal catalytic velocity. The presence of serpin Z4 stabilizes β-amylase activity during heat treatment without affecting its critical denaturing temperature. Oxidative stress, simulated by the addition of CuCl2, leads to the formation of high molecular weight polymers of β-amylase similar to those detected in vivo. The polymers were cross-linked through disulfide bonds, the formation of which was repressed when serpin Z4 was present. The results suggest an unprecedented function for a plant seed serpin as a β-amylase-specific chaperone-like partner that could optimize β-amylase activity upon germination. This report is the first to describe a noninhibitory function for a serpin in plants.

Quantitative proteomics analysis reveals the tolerance of wheat to salt stress in response to Enterobacter cloacae SBP-8

Salinity stress adversely affects the plant growth and is a major constraint to agriculture. In the present study, we studied the role of plant growth promoting rhizobacterium (PGPR) Enterobacter cloacae SBP-8 possessing ACC deaminase activity on proteome profile of wheat (Triticum aestivum L.) under high salinity (200 mM NaCl) stress. The aim of study was to investigate the differential expressed protein in selected three (T-1, T-2, T-3) treatments and absolute quantification (MS/MS analysis) was used to detect statistically significant expressed proteins. In this study, we investigated the adaptation mechanisms of wheat seedlings exposed to high concentration of NaCl treatment (200 mM) for 15 days in response to bacterial inoculation based on proteomic data. The identified proteins were distributed in different cellular, biological and molecular functions. Under salt stress, proteins related to ion-transport, metabolic pathway, protein synthesis and defense responsive were increased to a certain extent. A broader comparison of the proteome of wheat plant under different treatments revealed that changes in some of the metabolic pathway may be involved in stress adaption in response to PGPR inoculation. Hierarchical cluster analysis identified the various up-regulated/down-regulated proteins into tested three treatments. Our results suggest that bacterial inoculation enhanced the ability of wheat plant to combat salt stress via regulation of transcription factors, promoting antioxidative activity, induction of defense enzymes, lignin biosynthesis, and acceleration of protein synthesis.

A structure-derived snap-trap mechanism of a multispecific serpin from the dysbiotic human oral microbiome

Enduring host-microbiome relationships are based on adaptive strategies within a particular ecological niche. Tannerella forsythia is a dysbiotic member of the human oral microbiome that inhabits periodontal pockets and contributes to chronic periodontitis. To counteract endopeptidases from the host or microbial competitors, T. forsythia possesses a serpin-type proteinase inhibitor called miropin. Although serpins from animals, plants, and viruses have been widely studied, those from prokaryotes have received only limited attention. Here we show that miropin uses the serpin-type suicidal mechanism. We found that, similar to a snap trap, the protein transits from a metastable native form to a relaxed triggered or induced form after cleavage of a reactive-site target bond in an exposed reactive-center loop. The prey peptidase becomes covalently attached to the inhibitor, is dragged 75 Å apart, and is irreversibly inhibited. This coincides with a large conformational rearrangement of miropin, which inserts the segment upstream of the cleavage site as an extra β-strand in a central β-sheet. Standard serpins possess a single target bond and inhibit selected endopeptidases of particular specificity and class. In contrast, miropin uniquely blocked many serine and cysteine endopeptidases of disparate architecture and substrate specificity owing to several potential target bonds within the reactive-center loop and to plasticity in accommodating extra β-strands of variable length. Phylogenetic studies revealed a patchy distribution of bacterial serpins incompatible with a vertical descent model. This finding suggests that miropin was acquired from the host through horizontal gene transfer, perhaps facilitated by the long and intimate association of T. forsythia with the human gingiva.

Proteomics of Durum Wheat Grain during Transition to Conservation Agriculture

Nitrogen management in combination with sustainable agronomic techniques can have a great impact on the wheat grain proteome influencing its technological quality. In this study, proteomic analyses were used to document changes in the proportion of prolamins in mature grains of the newly released Italian durum wheat cv Achille. Such an approach was applied to wheat fertilized with urea (UREA) and calcium nitrate (NITRATE), during the transition to no-till Conservation Agriculture (CA) practice in a Mediterranean environment. Results obtained in a two-years field experiment study suggest low molecular weight glutenins (LMW-GS) as the fraction particularly inducible regardless of the N-form. Quantitative analyses of LMW-GS by 2D-GE followed by protein identification by LC-ESI-MS/MS showed that the stable increase was principally due to C-type LMW-GS. The highest accumulation resulted from a physiologically healthier state of plants treated with UREA and NITRATE. Proteomic analysis on the total protein fraction during the active phase of grain filling was also performed. For both N treatments, but at different extent, an up-regulation of different classes of proteins was observed: i) enzymes involved in glycolysis and citric acid cycles which contribute to an enhanced source of energy and carbohydrates, ii) stress proteins like heat shock proteins (HSPs) and antioxidant enzymes, such as peroxidases and superoxide dismutase which protect the grain from abiotic stress during starch and storage protein synthesis. In conclusion N inputs, which combined rate with N form gave high yield and improved quality traits in the selected durum wheat cultivar. The specific up-regulation of some HSPs, antioxidant enzymes and defense proteins in the early stages of grain development and physiological indicators related to fitness traits, could be useful bio-indicators, for wheat genotype screening under more sustainable agronomic conditions, like transition phase to no-till CA in Mediterranean environments.

Proteomic analysis of mature barley grains from C-hordein antisense lines

Hordeins are the major storage proteins in barley grains and are responsible for their low nutritional quality. Previously, antisense C-hordein barley lines were generated and were shown to contain a more balanced amino acid composition and an altered storage protein profile. In the present study, a proteomic approach that combined two-dimensional gel electrophoresis (2-DE) and mass spectrometry was used to (1) identify the changes in the protein profile of non-storage proteins (salt soluble fraction) in antisense C-hordein barley lines (L1, L2 and L3) and (2) map the differentially expressed proteins compared to the non-transgenic control line (Hordeum vulgare cv. Golden Promise). Moreover, the changes in the proteins were correlated with the more balanced amino acid composition of these lines, with special attention to the lysine content. The results showed that suppression of C-hordein expression does not exclusively affect hordein synthesis and accumulation. The more balanced amino acid composition observed in the transgenic lines L1, L2 and L3 was an indirect result of the profound alterations in the patterns of the non-storage proteins. The observed changes included up-regulated expression of the proteins involved in stress and detoxification (L1), defence (L2 and L3), and storage globulins (L1, L2 and L3). To a lesser extent, the proteins involved in grain metabolism were also changed. Thus, the increased essential amino acids content results from changes in distinct protein sources among the three antisense C-hordein lines analyzed, although the up-regulated expression of lysine-rich proteins was consistently observed in all lines.

Distinct metabolic changes between wheat embryo and endosperm during grain development revealed by 2D-DIGE-based integrative proteome analysis

Two Chinese bread wheat cultivars, Jinghua 9 and Zhongmai 175, distinct in grain weight and dough quality, were used to study proteome changes in the embryo and endosperm during grain development using a two-dimensional difference gel electrophoresis (2D-DIGE)-based proteomics approach. In total, 138 and 127 differentially expressed protein (DEP) spots representing 116 and 113 unique DEPs were identified in the embryo and endosperm, respectively. Among them, 54 (31%) DEPs were commonly present in both organs while 62 (35%) and 59 (34%) DEPs occurred only in the embryo and endosperm, respectively. Embryonic DEPs are primarily stress-related proteins and involved in carbohydrate and lipid metabolism, while those from the endosperm are related primarily to carbohydrate metabolism and storage. Principal component analysis (PCA) indicated that the proteome differences in the endosperm caused by different cultivars were greater than those by development stages, while the differences in the embryo showed the opposite pattern. Protein-protein interaction (PPI) analysis revealed a complex network centered primarily on enzymes involved in carbohydrate and protein metabolism. The transcriptional levels of fourteen important DEPs encoding genes showed high similarity between organs and cultivars. In particular, some key DEPs of the endosperm, such as phosphoglucomutase, ADP-glucose pyrophosphorylase (AGPase), and sucrose synthase (SUS), showed significantly upregulated expression, indicating their key roles in starch biosynthesis and grain yield. Moreover, upregulated expression of some storage proteins in the endosperm could improve wheat bread-making quality.

Proteomics of Durum Wheat Grain during Transition to Conservation Agriculture

Nitrogen management in combination with sustainable agronomic techniques can have a great impact on the wheat grain proteome influencing its technological quality. In this study, proteomic analyses were used to document changes in the proportion of prolamins in mature grains of the newly released Italian durum wheat cv Achille. Such an approach was applied to wheat fertilized with urea (UREA) and calcium nitrate (NITRATE), during the transition to no-till Conservation Agriculture (CA) practice in a Mediterranean environment. Results obtained in a two-years field experiment study suggest low molecular weight glutenins (LMW-GS) as the fraction particularly inducible regardless of the N-form. Quantitative analyses of LMW-GS by 2D-GE followed by protein identification by LC-ESI-MS/MS showed that the stable increase was principally due to C-type LMW-GS. The highest accumulation resulted from a physiologically healthier state of plants treated with UREA and NITRATE. Proteomic analysis on the total protein fraction during the active phase of grain filling was also performed. For both N treatments, but at different extent, an up-regulation of different classes of proteins was observed: i) enzymes involved in glycolysis and citric acid cycles which contribute to an enhanced source of energy and carbohydrates, ii) stress proteins like heat shock proteins (HSPs) and antioxidant enzymes, such as peroxidases and superoxide dismutase which protect the grain from abiotic stress during starch and storage protein synthesis. In conclusion N inputs, which combined rate with N form gave high yield and improved quality traits in the selected durum wheat cultivar. The specific up-regulation of some HSPs, antioxidant enzymes and defense proteins in the early stages of grain development and physiological indicators related to fitness traits, could be useful bio-indicators, for wheat genotype screening under more sustainable agronomic conditions, like transition phase to no-till CA in Mediterranean environments.

Effect of 7H(ch) Hordeum chilense chromosome introgressions on the wheat endosperm proteomic profile

Hordeum chilense is an excellent genetic resource for wheat breeding due to its potential to improve breadmaking quality and nutritional value and provide resistance to some biotic and abiotic stresses. Hexaploid wheat lines carrying chromosome 7H(ch) introgressions, namely, chromosome additions of the whole chromosome 7H(ch) or the 7H(ch)α or the 7H(ch)β chromosome arms, and chromosome substitutions of the homeologous chromosomes 7A, 7B, or 7D by chromosome 7H(ch) were compared by 2D-PAGE analysis to study the effect of these alien introgressions on the wheat endosperm proteome. The addition of the 7H(ch)α chromosome arm did not alter the profile of most glutenins and gliadins, but showed higher quantities of puroindolines and lower xylanase inhibitors, which might improve also resistance to plant pathogens. On the other hand, (7A)7H(ch) or (7D)7H(ch) substitution lines showed enhanced avenin-like b proteins and triticin levels but reduced puroindolines, which could be desirable to improve dough properties and nutritional value and increase kernel hardness in wheat.

Proteomics, peptidomics, and immunogenic potential of wheat beer (Weissbier)

Wheat beer is a traditional light-colored top-fermenting beer brewed with at least 50% malted (e.g., German Weissbier) or unmalted (e.g., Belgian Witbier) wheat (Triticum aestivum) as an adjunct to barley (Hordeum vulgare) malt. For the first time, we explored the proteome of three Weissbier samples, using both 2D electrophoresis (2DE)-based and 2DE-free strategies. Overall, 58 different gene products arising from barley, wheat, and yeast (Saccharomyces spp.) were identified in the protein fraction of a representative Weissbier sample analyzed in detail. Analogous to all-barley-malt beers (BMB), barley and wheat Z-type serpins and nonspecific lipid transfer proteins dominated the proteome of Weissbier. Several α-amylase/trypsin inhibitors also survived the harsh brewing conditions. During brewing, hundreds of peptides are released into beer. By liquid chromatography-electrospray tandem mass spectrometry (LC-ESI MS/MS) analysis, we characterized 167 peptides belonging to 44 proteins, including gliadins, hordeins, and high- and low-molecular-weight glutenin subunits. Because of the interference from the overabundant yeast-derived peptides, we identified only a limited number of epitopes potentially triggering celiac disease. However, Weissbier samples contained 374, 372, and 382 ppm gliadin-equivalent peptides, as determined with the competitive G12 ELISA, which is roughly 10-fold higher than a lager BMB (41 ppm), thereby confirming that Weissbier is unsuited for celiacs. Western blot analysis demonstrated that Weissbier also contained large-sized prolamins immunoresponsive to antigliadin IgA antibodies from the pooled sera of celiac patients (n = 4).

Miropin, a novel bacterial serpin from the periodontopathogen Tannerella forsythia, inhibits a broad range of proteases by using different peptide bonds within the reactive center loop

All prokaryotic genes encoding putative serpins identified to date are found in environmental and commensal microorganisms, and only very few prokaryotic serpins have been investigated from a mechanistic standpoint. Herein, we characterized a novel serpin (miropin) from the human pathogen Tannerella forsythia, a bacterium implicated in initiation and progression of human periodontitis. In contrast to other serpins, miropin efficiently inhibited a broad range of proteases (neutrophil and pancreatic elastases, cathepsin G, subtilisin, and trypsin) with a stoichiometry of inhibition of around 3 and second-order association rate constants that ranged from 2.7 × 10(4) (cathepsin G) to 7.1 × 10(5) m(-1)s(-1) (subtilisin). Inhibition was associated with the formation of complexes that were stable during SDS-PAGE. The unusually broad specificity of miropin for target proteases is achieved through different active sites within the reactive center loop upstream of the P1-P1' site, which was predicted from an alignment of the primary structure of miropin with those of well studied human and prokaryotic serpins. Thus, miropin is unique among inhibitory serpins, and it has apparently evolved the ability to inhibit a multitude of proteases at the expense of a high stoichiometry of inhibition and a low association rate constant. These characteristics suggest that miropin arose as an adaptation to the highly proteolytic environment of subgingival plaque, which is exposed continually to an array of host proteases in the inflammatory exudate. In such an environment, miropin may function as an important virulence factor by protecting bacterium from the destructive activity of neutrophil serine proteases. Alternatively, it may act as a housekeeping protein that regulates the activity of endogenous T. forsythia serine proteases.

Specific nongluten proteins of wheat are novel target antigens in celiac disease humoral response

While the antigenic specificity and pathogenic relevance of immunologic reactivity to gluten in celiac disease have been extensively researched, the immune response to nongluten proteins of wheat has not been characterized. We aimed to investigate the level and molecular specificity of antibody response to wheat nongluten proteins in celiac disease. Serum samples from patients and controls were screened for IgG and IgA antibody reactivity to a nongluten protein extract from the wheat cultivar Triticum aestivum Butte 86. Antibodies were further analyzed for reactivity to specific nongluten proteins by two-dimensional gel electrophoresis and immunoblotting. Immunoreactive molecules were identified by tandem mass spectrometry. Compared with healthy controls, patients exhibited significantly higher levels of antibody reactivity to nongluten proteins. The main immunoreactive nongluten antibody target proteins were identified as serpins, purinins, α-amylase/protease inhibitors, globulins, and farinins. Assessment of reactivity toward purified recombinant proteins further confirmed the presence of antibody response to specific antigens. The results demonstrate that, in addition to the well-recognized immune reaction to gluten, celiac disease is associated with a robust humoral response directed at a specific subset of the nongluten proteins of wheat.

Rising CO2 concentration altered wheat grain proteome and flour rheological characteristics

Wheat cv. H45 was grown under ambient CO2 concentration and Free Air CO2 Enrichment (FACE; e[CO2], ∼550 μmol CO2 mol(-1)). The effect of FACE on wheat grain proteome and associated changes in the flour rheological properties was investigated. A comparative proteomic analysis was performed using 2-D-DIGE followed by MALDI/TOF-MS. Total grain protein concentration was decreased by 9% at e[CO2]. Relative abundance of three high molecular weight glutenin sub units (HMW-GS) were decreased at e[CO2]. In contrast, relative abundance of serpins Z1C and 1-Cys peroxiredoxin was increased at e[CO2]. Elevated [CO2] also decreased the bread volume (by 11%) and dough strength (by 7%) while increased mixing time. However, dough extensibility and dough stability were unchanged at elevated [CO2]. These findings suggest that e[CO2] has a major impact on gluten protein concentration which is associated lower bread quality at e[CO2].

Characterization of barley serpin Z7 that plays multiple roles in malt and beer

Barley protein Z7 (BSZ7) is a well-known serine protease inhibitor that was regarded as a major effector of beer foam stability. Moreover, it has also been suggested to participate in haze formation and affect wort filterability. The present study purified BSZ7 from barley malt and characterized its secondary structure and modification, as well as its relationship with peroxidase, to elucidate the molecular base of BSZ7 that supports its multiple roles in malt and beer. It was found that after 30 min of heating, the secondary structure was not affected. BSZ7 has no inhibiting effect on nonspecific protease originated from malt, suggesting its negative role in wort filterability was accomplished by other means. Furthermore, the glycation of BSZ7 by the Maillard reaction may make some contribution to its survival during wort boiling. The interaction of BSZ7 with polysaccharides and polyphenols found by adding experiment may explain how it acts as a negative factor on wort filterability. Greater understanding of BSZ7 and other proteins of malts will lead to better improvements in brewing quality.

Protein composition of wheat gluten polymer fractions determined by quantitative two-dimensional gel electrophoresis and tandem mass spectrometry

Background

Certain wheat gluten proteins form large protein polymers that are extractable in 0.5% SDS only after sonication. Although there is a strong relationship between the amounts of these polymers in the flour and bread-making quality, the protein components of these polymers have not been thoroughly investigated.

Results

Flour proteins from the US bread wheat Butte 86 were extracted in 0.5% SDS using a two-step procedure with and without sonication. Proteins were further separated by size exclusion chromatography (SEC) into monomeric and polymeric fractions and analyzed by quantitative two-dimensional gel electrophoresis (2-DE). When proteins in select 2-DE spots were identified by tandem mass spectrometry (MS/MS), overlapping spots from the different protein fractions often yielded different identifications. Most high-molecular-weight glutenin subunits (HMW-GS) and low-molecular-weight glutenin subunits (LMW-GS) partitioned into the polymer fractions, while most gliadins were found in the monomer fractions. The exceptions were alpha, gamma and omega gliadins containing odd numbers of cysteine residues. These proteins were detected in all fractions, but comprised the largest proportion of the SDS-extractable polymer fraction. Several types of non-gluten proteins also were found in the polymer fractions, including serpins, triticins and globulins. All three types were found in the largest proportions in the SDS-extractable polymer fraction.

Conclusions

This is the first study to report the accumulation of gliadins containing odd numbers of cysteine residues in the SDS-extractable glutenin polymer fraction, supporting the hypothesis that these gliadins serve as chain terminators of the polymer chains. These data make it possible to formulate hypotheses about how protein composition influences polymer size and structure and provide a foundation for future experiments aimed at determining how environment affects glutenin polymer distribution. In addition, the analysis revealed additional layers of complexity to the wheat flour proteome that should be considered when evaluating quantitative 2-DE data.

Wheat seed proteins regulated by imbibition independent of dormancy status

Seed dormancy is an important trait in wheat (Trticum aestivum L.) and it can be released by germination-stimulating treatments such as after-ripening. Previously, we identified proteins specifically associated with after-ripening mediated developmental switches of wheat seeds from the state of dormancy to germination. Here, we report seed proteins that exhibited imbibition induced co-regulation in both dormant and after-ripened seeds of wheat, suggesting that the expression of these specific proteins/protein isoforms is not associated with the maintenance or release of seed dormancy in wheat.

Integrated analysis of seed proteome and mRNA oxidation reveals distinct post-transcriptional features regulating dormancy in wheat (Triticum aestivum L.)

Wheat seeds can be released from a dormant state by after-ripening; however, the underlying molecular mechanisms are still mostly unknown. We previously identified transcriptional programmes involved in the regulation of after-ripening-mediated seed dormancy decay in wheat (Triticum aestivum L.). Here, we show that seed dormancy maintenance and its release by dry after-ripening in wheat is associated with oxidative modification of distinct seed-stored mRNAs that mainly correspond to oxidative phosphorylation, ribosome biogenesis, nutrient reservoir and α-amylase inhibitor activities, suggesting the significance of post-transcriptional repression of these biological processes in regulating seed dormancy. We further show that after-ripening induced seed dormancy release in wheat is mediated by differential expression of specific proteins in both dry and hydrated states, including those involved in proteolysis, cellular signalling, translation and energy metabolism. Among the genes corresponding to these proteins, the expression of those encoding α-amylase/trypsin inhibitor and starch synthase appears to be regulated by mRNA oxidation. Co-expression analysis of the probesets differentially expressed and oxidized during dry after-ripening along with those corresponding to proteins differentially regulated between dormant and after-ripened seeds produced three co-expressed gene clusters containing more candidate genes potentially involved in the regulation of seed dormancy in wheat. Two of the three clusters are enriched with elements that are either abscisic acid (ABA) responsive or recognized by ABA-regulated transcription factors, indicating the association between wheat seed dormancy and ABA sensitivity.

The role of thioredoxin h in protein metabolism during wheat (Triticum aestivum L.) seed germination

Thioredoxin h can regulate the redox environment in the cell and play an important role in the germination of cereals. In the present study, the thioredoxin s antisense transgenic wheat with down-regulation of thioredoxin h was used to study the role of thioredoxin h in protein metabolism during germination of wheat seeds, and to explore the mechanism of the thioredoxin s antisense transgenic wheat seeds having high resistance to pre-harvest sprouting. The qRT-PCR results showed that the expression of protein disulfide isomerase in the thioredoxin s antisense transgenic wheat was up-regulated, which induced easily forming glutenin macropolymers and the resistance of storage proteins to degradation. The expression of serine protease inhibitor was also up-regulated in transgenic wheat, which might be responsible for the decreased activity of thiocalsin during the germination. The expression of WRKY6 in transgenic wheat was down-regulated, which was consistent with the decreased activity of glutamine oxoglutarate aminotransferase. In transgenic wheat, the activities of glutamate dehydrogenase, glutamic pyruvic transaminase and glutamic oxaloacetic transaminase were down-regulated, indicating that the metabolism of amino acid was lower than that in wild-type wheat during seed germination. A putative model for the role of thioredoxin h in protein metabolism during wheat seed germination was proposed and discussed.

Molecular and immunological characterization of wheat Serpin (Tri a 33)

SCOPE

Several wheat proteins are responsible for food and respiratory allergies. Due to their large polymorphism, the allergenic potential of a number of them has not yet been precisely established. The aim of this work was to perform a thorough assessment of serpin (Tri a 33) allergenicity.

METHODS AND RESULTS

Recombinant wheat Serpin-Z2B isoform (rSerpin-Z2B) was expressed in Escherichia coli. Synchrotron radiation circular dichroism data indicated that the recombinant serpin contains slightly more β-strands than α-helix structures. IgE reactivity of sera from 103 patients with food allergy and 29 patients with Baker's asthma was evaluated using ELISA, a model of basophil activation and linear epitope mapping (Pepscan). Twenty percent of patients with food allergy to wheat and 31% of those with Baker's asthma displayed rSerpin-Z2B-specific IgE in ELISA. The protein was able to induce IgE-dependent basophil degranulation. The Pepscan experiment identified four regions involved in IgE binding to serpin. Heating the protein induced its irreversible denaturation and impaired IgE binding, revealing the predominance of conformational epitopes.

CONCLUSION

This study confirms wheat serpin allergenicity and shows that recombinant serpin may be a marker of a broad spectrum of sensitization to wheat proteins.

Serpins in rice: protein sequence analysis, phylogeny and gene expression during development

BACKGROUND

Most members of the serpin family of proteins are potent, irreversible inhibitors of specific serine or cysteine proteinases. Inhibitory serpins are distinguished from members of other families of proteinase inhibitors by their metastable structure and unique suicide-substrate mechanism. Animal serpins exert control over a remarkable diversity of physiological processes including blood coagulation, fibrinolysis, innate immunity and aspects of development. Relatively little is known about the complement of serpin genes in plant genomes and the biological functions of plant serpins.

RESULTS

A structurally refined amino-acid sequence alignment of the 14 full-length serpins encoded in the genome of the japonica rice Oryza sativa cv. Nipponbare (a monocot) showed a diversity of reactive-centre sequences (which largely determine inhibitory specificity) and a low degree of identity with those of serpins in Arabidopsis (a eudicot). A new convenient and functionally informative nomenclature for plant serpins in which the reactive-centre sequence is incorporated into the serpin name was developed and applied to the rice serpins. A phylogenetic analysis of the rice serpins provided evidence for two main clades and a number of relatively recent gene duplications. Transcriptional analysis showed vastly different levels of basal expression among eight selected rice serpin genes in callus tissue, during seedling development, among vegetative tissues of mature plants and throughout seed development. The gene OsSRP-LRS (Os03g41419), encoding a putative orthologue of Arabidopsis AtSerpin1 (At1g47710), was expressed ubiquitously and at high levels. The second most highly expressed serpin gene was OsSRP-PLP (Os11g11500), encoding a non-inhibitory serpin with a surprisingly well-conserved reactive-centre loop (RCL) sequence among putative orthologues in other grass species.

CONCLUSIONS

The diversity of reactive-centre sequences among the putatively inhibitory serpins of rice point to a range of target proteases with different proteolytic specificities. Large differences in basal expression levels of the eight selected rice serpin genes during development further suggest a range of functions in regulation and in plant defence for the corresponding proteins.