From Storage Compartment to Lytic Organelle: The Metamorphosis of the Aleurone Protein Storage Vacuole

Protein storage vacuoles are found in a variety of tissues butare especially abundant in the storage organs of fruits andseeds. In this review, we focus on the protein storage vacuolesof cereal aleurone. In the mature grain, these organelles arerepositories for reserve nitrogen, carbon and minerals. Followingimbibition, protein storage vacuoles of cereal aleurone changefrom storage compartments to lytic organelles. Changes in proteinstorage vacuole structure and enzymatic activity during thistransition are discussed. It is emphasized that protein storagevacuoles are poised for reserve mobilization, and that gibberellinperception by the aleurone cell initiates a signalling cascadethat promotes acidification of the vacuole lumen and activationof enzymes and transporters.Copyright 1998 Annals of BotanyCompany Protein storage vacuole, cereal aleurone, gibberellin, abscisic acid, protein body, endosperm reserves.     

酿酒酵母胞质内NADH的代谢调控

酿酒酵母(Saccharomyces cerevisiae)的生长过程有大量的胞内NADH产生。有氧途径中,胞外的NADH脱氢酶、三磷酸甘油穿梭酶系是线粒体内NADH氧化的最主要机制。该文主要讨论以下三个方面的内容:不同生理环境下促成线粒体胞内NADH氧化的各主要机制的作用;借助电子传递链开启NADH从胞质脱氢酶到线粒体的通道,各代谢动力学的有序进行;各种酶形成超分子复合物,尤其是起关键调控作用的酶形成具相似生理功能的高整合性功能酶。     

Assembly and transport of seed storage proteins

Plant seeds store nitrogen by accumulating storage proteins in protein bodies within various compartments of the endomembrane system. The prolamin storage proteins of some cereal species are normally retained and assembled into protein bodies within the ER. Yet, these proteins lack a C-terminal KDEL/HDEL signal, suggesting that their retention is regulated by novel mechanisms. Furthermore, in other cereal species, such protein bodies formed within the ER may be subsequently internalized into vacuoles by a special route that does not utilize the Golgi complex. Thus, studies of the routing of seed storage proteins are revealing novel mechanisms of protein assembly and transport in the endomembrane system.     

Cereal seed storage proteins: structures, properties and role in grain utilization

Storage proteins account for about 50% of the total protein in mature cereal grains and have important impacts on their nutritional quality for humans and livestock and on their functional properties in food processing. Current knowledge of the structures and properties of the prolamin and globulin storage proteins of cereals and their mechanisms of synthesis, trafficking and deposition in the developing grain is briefly reviewed here. The role of the gluten proteins of wheat in determining the quality of the grain for breadmaking and how their amount and composition can be manipulated leading to changes in dough mixing properties is also discussed.     

Transgenic barley expressing a fungal xylanase gene in the endosperm of the developing grains

The feasibility of producing plant cell wall polysaccharide-hydrolysing feed enzymes in the endosperm of barley grain was investigated. The coding region of a modified xylanase gene (xynA) from the rumen fungus, Neocallimastix patriciarum, linked with an endosperm-specific promoter from cereal storage protein genes was introduced into barley by Agrobacterium-mediated transformation. Twenty-four independently transformed barley lines with the xylanase gene were produced and analysed. The fungal xylanase was produced in the developing endosperm under the control of either the rice glutelin B-1 (GluB-1) or barley B1 hordein (Hor2-4) promoter. The rice GluB-1 promoter provided an apparently higher expression level of recombinant proteins in barley grain than the barley Hor2-4 promoter in both transient and stable expression experiments. In particular, the mean value for the fungal xylanase activity driven by the GluB-1 promoter in the mature grains of transgenic barley was more than twice that with the Hor2-4 promoter. Expression of the xylanase transgene under these endosperm-specific promoters was not observed in the leaf, stem and root tissues. Accumulation of the fungal xylanase in the developing grains of transgenic barley followed the pattern of storage protein deposition. The xylanase was stably maintained in the grain during grain maturation and desiccation and post-harvest storage. These results indicate that the cereal grain expression system may provide an economic means for large scale production of feed enzymes in the future.     

Proteomic analysis of developing rye grain with contrasting resistance to preharvest sprouting

Significant differences in the two-dimensional electrophoresis patterns of proteins from developing rye grain were found to be associated with resistance and susceptibility to preharvest sprouting (PHS). Mass spectrometry of individual spots showing different abundance in PHS-resistant and PHS-susceptible lines identified proteins involved in: reaction to biotic and abiotic stresses, including oxidative stress, energy metabolism and regulation of gene expression. Highly differentiated abundance of proteins found in developing grain suggest that the diversification of processes leading to developing PHS resistance or PHS susceptibility starts from an early stage of grain development. A part of the identified proteins in rye grain were also reported to be associated with PHS in wheat and rice, which suggests that some mechanisms affecting precocious germination might be common for different cereal species.     

Inhibitory serpins from rye grain with glutamine as P1 and P2 residues in the reactive center

Six of seven serpins detected in grains of rye (Secale cereale) were purified and characterized. The amino acid sequence close to the blocked N-terminus, the reactive center loop sequence and the second order association rate constant (k(a)') for irreversible complex formation with chymotrypsin were determined for each serpin. Three of four serpins containing the unusual reactive center P2-P1' QQ/S and one with P2-P1' PQ/M were equally efficient inhibitors of chymotrypsin (k(a)' approximately 10(5) M(-1) s(-1)). One serpin with P2-P1' PY/M was a faster inhibitor (k(a)' approximately 10(6) M(-1) s(-1)). Similar but differently organized glutamine-rich reactive centers were recently found in grain serpins cloned from wheat [Ostergaard et al. (2000) J. Biol. Chem. 275, 33272] but not from barley. The prolamin storage proteins of cereal grains contain similar sequences in their glutamine-rich repeats. A possible adaption of hypervariable serpin reactive centers late in Triticeae cereal evolution as defence against insects feeding on cereal grains is discussed.     

The Development of Protein Bodies in the Storage Tissues1

Homogenates of the developing endosperms of maize, wheat, andbarley and of developing cotyledons of peas have been separatedon sucrose density gradients. Protein bodies have been recognizedby their content of storage proteins, their density, and theirappearance under the electron microscope. The distribution ofthe endoplasmic reticulum was followed by measuring NADH-cytochromec reductase. Glutamate dehydrogenase, catalase, and triose phosphatedehydrogenase—respectively marker enzymes for mitochondria,microbodies, and plastids—were also present in the gradients.Differences were found between the different species with respectto the association between the endoplasmic reticulum and thestorage proteins. There was no evidence for any vacuolar markerenzymes associated with the cereal protein bodies. The proteinbodies of wheat and barley appear to be similar to each otherbut differ from maize in that the latter have much more endoplasmicreticulum associated with them. In contrast the protein bodiesof peas co-sediment with vacuolar marker enzymes.     

A novel bioinformatics approach identifies candidate genes for the synthesis and feruloylation of arabinoxylan

Arabinoxylans (AXs) are major components of graminaceous plant cell walls, including those in the grain and straw of economically important cereals. Despite some recent advances in identifying the genes encoding biosynthetic enzymes for a number of other plant cell wall polysaccharides, the genes encoding enzymes of the final stages of AX synthesis have not been identified. We have therefore adopted a novel bioinformatics approach based on estimation of differential expression of orthologous genes between taxonomic divisions of species. Over 3 million public domain cereal and dicot expressed sequence tags were mapped onto the complete sets of rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana) genes, respectively. It was assumed that genes in cereals involved in AX biosynthesis would be expressed at high levels and that their orthologs in dicotyledonous plants would be expressed at much lower levels. Considering all rice genes encoding putative glycosyl transferases (GTs) predicted to be integral membrane proteins, genes in the GT43, GT47, and GT61 families emerged as much the strongest candidates. When the search was widened to all other rice or Arabidopsis genes predicted to encode integral membrane proteins, cereal genes in Pfam family PF02458 emerged as candidates for the feruloylation of AX. Our analysis, known activities, and recent findings elsewhere are most consistent with genes in the GT43 families encoding beta-1,4-xylan synthases, genes in the GT47 family encoding xylan alpha-1,2- or alpha-1,3-arabinosyl transferases, and genes in the GT61 family encoding feruloyl-AX beta-1,2-xylosyl transferases.     

Metal complexes as inhibitors of the 26S proteasome in tumor cells

The ubiquitin/proteasome pathway is the main mechanism available for eukaryotic cells to eliminate defective proteins and enzymes. Tumor cells -particularly those in solid tumors such as prostate cancer- seem to display increased proteasomal activity associated to cell growth. When such activity is inhibited apoptotic cell death takes place. Thus, the understanding of the chemical mechanisms by which this inhibition occurs is relevant to the development of new therapeutic antineoplastic agents. Here a short review is presented on the synthesis, characterization, and activity of metal-containing species with asymmetric ligands containing the methylpyridin-amino-methylphenol moiety. These complexes were scrupulously investigated structurally and spectroscopically, and have been shown to inhibit the chymotrypsin-like activity of the 20S and 26S proteasome in vitro and in vivo. Recent developments in the understanding of such inhibition are discussed and point out to the influence exerted by ligand substituents, the electronic configurations and charges of the metal ion, and the role of counterions.     

Organization and regulation of the cytosolic NADH metabolism in the yeast Saccharomyces cerevisiae

Keeping a cytosolic redox balance is a prerequisite for living cells in order to maintain a metabolic activity and enable growth. During growth of Saccharomyces cerevisiae, an excess of NADH is generated in the cytosol. Aerobically, it has been shown that the external NADH dehydrogenase, Nde1p and Nde2p, as well as the glycerol-3-phosphate dehydrogenase shuttle, comprising the cytoplasmic glycerol-3-phosphate dehydrogenase, Gpdlp, and the mitochondrial glycerol-3-phosphate dehydrogenase, Gut2p, are the most important mechanisms for mitochondrial oxidation of cytosolic NADH. In this review we summarize the recent results showing (i) the contribution of each of the mechanisms involved in mitochondrial oxidation of the cytosolic NADH, under different physiological situations; (ii) the kinetic and structural properties of these metabolic pathways in order to channel NADH from cytosolic dehydrogenases to the inner mitochondrial membrane and (iii) the organization in supramolecular complexes and, the peculiar ensuing kinetic regulation of some of the enzymes (i.e. Gut2p inhibition by external NADH dehydrogenase activity) leading to a highly integrated functioning of enzymes having a similar physiological function. The cell physiological consequences of such an organized and regulated network are discussed.     

Molecular pharming in cereal crops

There are many different agricultural expression systems that can be used for the large-scale production of recombinant proteins, but field-grown cereal crops are among the most attractive because recombinant proteins can be targeted to accumulate in the seed, and specifically in the endosperm, which has evolved naturally as a protein storage tissue. Within the developing endosperm, proteins are supplied with molecular chaperones and disulfide isomerases to facilitate folding and assembly, while the mature tissue is desiccated to prevent proteolytic degradation. Proteins expressed in cereal seeds can therefore remain stable for years in ambient conditions. Recent basic research has revealed a surprising diversity of protein targeting mechanisms in the endosperm, which can help to control post-translational modification and accumulation. Applied research and commercial development has seen several pharmaceutical proteins produced in cereals reach late stage preclinical development and the first clinical trials, with a number of companies now dedicated to developing cereal-based production platforms. In this review we discuss the basic science of molecular pharming in cereals, some of the lead product candidates, and challenges that remain to be addressed including the emerging regulatory framework for plant-made pharmaceuticals.     

The pivotal role of glutamate dehydrogenase (GDH) in the mobilization of N and C from storage material to asparagine in germinating seeds of yellow lupine

In germinating seeds of legumes, amino acids liberated during mobilization of storage proteins are partially used for synthesis of storage proteins of the developing axis, but some of them are respired. The amino acids are catabolized by both glutamate dehydrogenase (GDH) and transaminases. Ammonium is reassimilated by glutamine synthetase (GS) and, through the action of asparagine synthetase (AS), is stored in asparagine (Asn).This review presents the ways in which amino acids are converted into Asn and their regulation, mostly in germinating seeds of yellow lupine, where Asn can make up to 30% of dry matter. The energy balance of the synthesis of Asn from glutamate, the most common amino acid in lupine storage proteins, also shows an adaptation of lupine for oxidation of amino acids in early stages of germination.Regulation of the pathway of Asn synthesis is described with regard to the role of GDH and AS, as well as compartmentation of particular metabolites. The regulatory effect of sugar on major links of the pathway (mobilization of storage proteins, induction of genes and activity of GDH and AS) is discussed with respect to recent genetic and molecular studies. Moreover, the effect of glutamate and phytohormones is presented at various stages of Asn biosynthesis.     

Management of Sitotroga cerealella in stored cereal grains: a review

The economic loss due to pest attack in stored commodities is a serious problem worldwide. About 200 insect species attack stored commodities. These insect pests are responsible for quantitative and qualitative losses in cereal grains. Among the stored grain pests, Angoumois grain moth, Sitotroga cerealella is considered as common, top of the list and most destructive pest of cereal grains. Its infestation starts in the standing crop and continues in storage. Although there are many control strategies, our need is some effective, cheap and readily available strategy for safe storage. This review presents different ways by which S. cerealella can be controlled. In this paper, a list of approaches is given which are used to improve the protection of stored grains against S. cerealella attack. These approaches include use of edible oils, containers, synthetic chemicals, agricultural waste materials, plant derivatives, bacterial protoxins, biopesticides, biocontrol enhancers and semiochemicals. If these tactics are followed as combined strategies in a compatible manner, they can provide us an integrated pest management programme for the efficient control of S. cerealella in cereal grains.     

<Emphasis Type="Italic">Pichia anomala</Emphasis> in grain biopreservation

Cereal grain is a major component of food and feed in large parts of the world. The microbial flora on cereal grains may interfere with hygiene and storage stability, palatability and bioavailability of minerals and proteins may depend on the composition of the microbial population. Therefore, it is of primary interest to control the microbial species present on cereal grain. Inoculation of the biocontrol yeast Pichia anomala to cereal feed grain improved feed hygiene by reduction of moulds and Enterobacteriaceae, and enhanced the nutritional value by increasing the protein content and reducing the concentration of the antinutritional compound phytate. P. anomala strains showed a high phytase activity, for some strains also considerable extracellular phytase activity was observed. A certain maximum in biomass concentration was never exceeded indicating cell density induced growth inhibition of P. anomala.     

Prehistoric land use as recorded in a lake-shore core at Lake Constance

The second part of a pollen profile from Hornstaad/Lake Constance (Germany), containing the Atlantic and Subboreal (6400 cal B.C. to 700 cal B.C.) is presented. The diagram has a sampling interval of 1 cm and an average time resolution of 10 years. The cereal curve provided the basis for cereal zones, which are used to classify the human impact. Twenty-six cereal zones can be distinguished, most of them divided into subzones, from 5500 cal B.C. to 700 cal B.C. They correspond to both known and, mostly, unknown settlements in the surrounding landscape from the Early Neolithic to the Late Bronze Age. Charcoal and chemical analyses as well as sediment accumulation, confirmed by accelerator dates, provide evidence for human impact on the environment.A contribution to the 8th IPC, Aix-en-Provence, Sept. 1992     

Co-ordination of DNA single strand break repair

DNA damaging agents generated as a consequence of endogenous metabolism or via exogenous factors can produce a wide variety of lesions in DNA. These include base damage, sites of base loss (abasic sites) and single strand breaks (SSBs). Moreover, reactive oxygen species (ROS) create more diversity by generating SSBs containing modified 3'-ends, such as those containing phosphate, phosphoglycolate and oxidative base damage. Ionising radiation also generates DNA base lesions in close proximity to SSBs. The majority of these non-bulky lesions in DNA are repaired by proteins involved in the base excision repair (BER) pathway. It is apparent that due to the complexity of these lesions, they may require individual subsets of BER proteins for repair. However, the mechanism unravelling the required enzymes and directing damage-specific repair of SSBs is unclear. In this review we will discuss recent studies that identify new enzymes and activities involved in the repair of SSBs containing modified ends and in particular outline the possible mechanisms involved in the co-ordinated repair of "damaged" SSBs that can not be resealed directly and require preliminary processing.     

Antioxidant enzymes as redox-based biomarkers: a brief review

The field of redox proteomics focuses to a large extent on analyzing cysteine oxidation in proteins under different experimental conditions and states of diseases. The identification and localization of oxidized cysteines within the cellular milieu is critical for understanding the redox regulation of proteins under physiological and pathophysiological conditions, and it will in turn provide important information that are potentially useful for the development of novel strategies in the treatment and prevention of diseases associated with oxidative stress. Antioxidant enzymes that catalyze oxidation/reduction processes are able to serve as redox biomarkers in various human diseases, and they are key regulators controlling the redox state of functional proteins. Redox regulators with antioxidant properties related to active mediators, cellular organelles, and the surrounding environments are all connected within a network and are involved in diseases related to redox imbalance including cancer, ischemia/reperfusion injury, neurodegenerative diseases, as well as normal aging. In this review, we will briefly look at the selected aspects of oxidative thiol modification in antioxidant enzymes and thiol oxidation in proteins affected by redox control of antioxidant enzymes and their relation to disease. [BMB Reports 2015; 48(4): 200-208]