Legume vicilins (7S storage globulins) inhibit yeast growth and glucose stimulated acidification of the medium by yeast cells

RNA silencing is a key regulatory mechanism in the biocontrol fungus Clonostachys rosea-wheat interactions

BACKGROUND

Small RNA (sRNAs)- mediated RNA silencing is emerging as a key player in host-microbe interactions. However, its role in fungus-plant interactions relevant to biocontrol of plant diseases is yet to be explored. This study aimed to investigate Dicer (DCL)-mediated endogenous and cross-kingdom gene expression regulation in the biocontrol fungus Clonostachys rosea and wheat roots during interactions.

RESULTS

C. rosea Δdcl2 strain exhibited significantly higher root colonization than the WT, whereas no significant differences were observed for Δdcl1 strains. Dual RNA-seq revealed the upregulation of CAZymes, membrane transporters, and effector coding genes in C. rosea, whereas wheat roots responded with the upregulation of stress-related genes and the downregulation of growth-related genes. The expression of many of these genes was downregulated in wheat during the interaction with DCL deletion strains, underscoring the influence of fungal DCL genes on wheat defense response. sRNA sequencing identified 18 wheat miRNAs responsive to C. rosea, and three were predicted to target the C. rosea polyketide synthase gene pks29. Two of these miRNAs (mir_17532_x1 and mir_12061_x13) were observed to enter C. rosea from wheat roots with fluorescence analyses and to downregulate the expression of pks29, showing plausible cross-kingdom RNA silencing of the C. rosea gene by wheat miRNAs.

CONCLUSIONS

We provide insights into the mechanisms underlying the interaction between biocontrol fungi and plant roots. Moreover, the study sheds light on the role of sRNA-mediated gene expression regulation in C. rosea-wheat interactions and provides preliminary evidence of cross-kingdom RNA silencing between plants and biocontrol fungi.

JcTI-PepI, a synthetic peptide bioinspired in the trypsin inhibitor from Jatropha curcas, presents potent inhibitory activity against C. krusei, a neglected pathogen

Antimicrobial resistance has been increasing globally, posing a global public health risk. It has prompted the scientific community to look for alternatives to traditional drugs. Antimicrobial Peptides (AMPs) have stood out in this context because they have the potential to control infectious diseases while causing no or little harm to mammalian cells. In the present study, three peptides, JcTI-PepI, JcTI-PepII, and JcTI-PepIII, were designed and tested for antimicrobial activity based on the primary sequence of JcTI-I, a 2S albumin with trypsin inhibitory activity from Jatropha curcas. JcTI-PepI strongly inhibited C. krusei growth, and it caused severe disruptions in cellular processes and cell morphology. C. krusei cells treated with JcTI-PepI showed indicative of membrane permeabilization and overproduction of Reactive Oxygen Species. Moreover, the yeast's ability to acidify the medium was severely compromised. JcTI-PepI was also effective against pre-formed biofilm and did not harm human erythrocytes and Vero cells. Overall, these characteristics indicate that JcTI-PepI is both safe and effective against C. krusei, an intrinsically resistant strain that causes serious health problems and is frequently overlooked. It implies that this peptide has a high potential for use as a new antimicrobial agent in the future.

Machaerium acutifolium lectin alters membrane structure and induces ROS production in Candida parapsilosis

Lectins are a group of widely distributed and structurally heterogeneous proteins of nonimmune origin. These proteins have the ability to interact with glycans present on cell surfaces and elicit diverse biological activities. Machaerium acutifolium lectin (MaL) is an N-acetyl-D-glucosamine-binding lectin that exhibits antinociceptive activity via transient receptor potential cation channel subfamily V member 1 (TRPV1). Lectins that have the ability to recognize and interact with N-acetyl-D-glucosamine residues are potential candidates for studies of fungicidal activity. In this work, we show that MaL has antifungal activity against Candida species, and we describe its mode of action towards Candida parapsilosis. MaL inhibited the growth of C. albicans and C. parapsilosis. However, MaL was more potent against C. parapsilosis. The candidacidal mode of action of MaL on C. parapsilosis involves enhanced cell permeabilization, alteration of the plasma membrane proton-pumping ATPase function (H+-ATPase), induction of oxidative stress, and DNA damage. MaL also exhibited antibiofilm activity and noncytotoxicity to Vero cells. These results indicate that MaL is a promising candidate for the future development of a new, natural, and safe drug for the treatment of infections caused by C. parapsilosis.

The rescue of botanical insecticides: A bioinspiration for new niches and needs

Crop protection is the basis of plant production and food security. Additionally, there are many efforts focused on increasing defensive mechanisms in order to avoid the damaging effects of insects, which still represent significant losses worldwide. Plants have naturally evolved different mechanisms to discourage herbivory, including chemical barriers such as the induction of defensive proteins and secondary metabolites, some of which have a historical link with bio-farming practices and others that are yet to be used. In the context of global concern regarding health and environmental impacts, which has been translated into political action and restrictions on the use of synthetic pesticides, this review deals with a description of some historical commercial phytochemicals and promising proteinaceous compounds that plants may modulate to defeat insect attacks. We present a broader outlook on molecular structure and mechanisms of action while we discuss possible tools to achieve effective methods for the biological control of pests, either by the formulation of products or by the development of new plant varieties with enhanced chemical defenses.

Narrow-Leafed Lupin (Lupinus angustifolius) β1- and β6-Conglutin Proteins Exhibit Antifungal Activity, Protecting Plants against Necrotrophic Pathogen Induced Damage from Sclerotinia sclerotiorum and Phytophthora nicotianae

Vicilins (7S globulins) are seed storage proteins and constitute the main protein family in legume seeds, particularly in narrow-leafed lupin (Lupinus angustifolius L.; NLL), where seven vicilin genes, called β1- to β7-conglutin have been identified. Vicilins are involved in germination processes supplying amino acids for seedling growth and plant development, as well as in some cases roles in plant defense and protection against pathogens. The roles of NLL β-conglutins in plant defense are unknown. Here the potential role of five NLL β-conglutin family members in protection against necrotrophic fungal pathogens was investigated and it was demonstrated that recombinant purified 6xHis-tagged β1- and β6-conglutin proteins exhibited the strongest in vitro growth inhibitory activity against a range of necrotrophic fungal pathogens compared to β2, β3, and β4 conglutins. To examine activity in vivo, two representative necrotrophic pathogens, the fungus Sclerotinia sclerotiorum and oomycete Phytophthora nicotianae were used. Transient expression of β1- and β6-conglutin proteins in Nicotiana benthamiana leaves demonstrated in vivo growth suppression of both of these pathogens, resulting in low percentages of hyphal growth and elongation in comparison to control treated leaves. Cellular studies using β1- and β6-GFP fusion proteins showed these conglutins localized to the cell surface including plasmodesmata. Analysis of cellular death following S. sclerotiorum or P. nicotianae revealed both β1- and β6-conglutins suppressed pathogen induced cell death in planta and prevented pathogen induced suppression of the plant oxidative burst as determined by protein oxidation in infected compared to mock-inoculated leaves.

Mo-CBP3, an antifungal chitin-binding protein from Moringa oleifera seeds, is a member of the 2S albumin family

Mo-CBP3 is a chitin-binding protein from M. oleifera seeds that inhibits the germination and mycelial growth of phytopathogenic fungi. This protein is highly thermostable and resistant to pH changes, and therefore may be useful in the development of new antifungal drugs. However, the relationship of MoCBP3 with the known families of carbohydrate-binding domains has not been established. In the present study, full-length cDNAs encoding 4 isoforms of Mo-CBP3 (Mo-CBP3-1, Mo-CBP3-2, Mo-CBP3-3 and Mo-CBP3-4) were cloned from developing seeds. The polypeptides encoded by the Mo-CBP3 cDNAs were predicted to contain 160 (Mo-CBP3-3) and 163 amino acid residues (Mo-CBP3-1, Mo-CBP3-2 and Mo-CBP3-4) with a signal peptide of 20-residues at the N-terminal region. A comparative analysis of the deduced amino acid sequences revealed that Mo-CBP3 is a typical member of the 2S albumin family, as shown by the presence of an eight-cysteine motif, which is a characteristic feature of the prolamin superfamily. Furthermore, mass spectrometry analysis demonstrated that Mo-CBP3 is a mixture of isoforms that correspond to different mRNA products. The identification of Mo-CBP3 as a genuine member of the 2S albumin family reinforces the hypothesis that these seed storage proteins are involved in plant defense. Moreover, the chitin-binding ability of Mo-CBP3 reveals a novel functionality for a typical 2S albumin.

Are vicilins another major class of legume lectins?

Legume lectins comprise a structurally related, Ca/Mn-dependent, widespread, abundant and well characterized lectin family when compared to the large number of lectins from other sources described in the literature. Strangely enough, no specific function has been assigned to them aside from a possible role in storage and/or defense. Using a recent and fine-tuned methodology capable of specific lectin identification, β-conglutin, Vicia faba vicilin and β-lathyrin, the vicilin storage globulins from Lupinus albus, V. faba and Lathyrus sativus, respectively, were shown to be capable of affinity binding to thoroughly washed erythrocyte membranes and of specific elution with appropriate sugars. Based on this evidence and on sparse data published in the literature, a second family of legume lectins is proposed: the 7S family of storage proteins from leguminous seeds, or family II of legume lectins. These lectins are also structurally related, widespread and well characterized. In addition, they self-aggregate in a Ca/Mg, electrostatic dependent manner and are even more abundant than the family I of legume lectins. Using the same evidence, reserve and defense roles may be attributed to family II of legume lectins.

Chemical composition, antioxidant activities and protein profiling of different parts of Allamanda cathartica

The phytochemical screening and protein profiling of Allamanda cathartica was performed. Biochemical analysis revealed that peroxidase (8730 ± 307 units/g), superoxide dismutase (181 ± 3.79 units/g), catalase (529 ± 28.9 units/g), protease (3598 ± 79.8 units/g), total phenolic contents (19,344 ± 657 μM/g), β-esterases (342 ± 46.5 units/g) and the total oxidant status were highest in the roots as compared to other plant parts. However, total soluble proteins (128 ± 1.54 mg/g), lycopene (5.70 ± 0.61 mg/g), chlorophyll a (161 ± 24.9 μg/g), total chlorophyll content (267 ± 34.3 μg/g) and total carotenoid content (12.4 ± 1.71 mg/g) were found to be highest in leaves. Moreover, total antioxidant capacity (5.43 ± 0.29 μM/g) detected by using ABTS method and α-esterase (714.580 ± 23.6 units/g) were highest in shoots. The protein profiling was performed using SDS-PAGE. In leaves, 13 peptides with molecular weight (M.wt.) from 27 to 168 kDa were detected while in shoots 10 peptides with M.wt. from 30 to 95 kDa were resolved. Similarly, in roots, 10 peptides of 30-880 kDa and in flower seven peptides of 30-88 kDa were detected.

Soybean toxin (SBTX) impairs fungal growth by interfering with molecular transport, carbohydrate/amino acid metabolism and drug/stress responses

Soybean toxin (SBTX) is an antifungal protein from soybeans with broad inhibitory activity against the growth and filamentation of many fungi, including human and plant pathogenic species such as Candida albicans, Candida parapsilosis, Aspergillus niger, Penicillium herquei, Cercospora sojina and Cercospora kikuchii. Understanding the mechanism by which SBTX acts on fungi and yeasts may contribute to the design of novel antifungal drugs and/or the development of transgenic plants resistant to pathogens. To this end, the polymorphic yeast C. albicans was chosen as a model organism and changes in the gene expression profile of strain SC5314 upon exposure to SBTX were examined. Genes that were differentially regulated in the presence of SBTX were involved in glucose transport and starvation-associated stress responses as well as in the control of both the induction and repression of C. albicans hyphal formation. Transmission electron microscopy showed that C. albicans cells exposed to SBTX displayed severe signs of starvation and were heavily granulated. Our data were indicative of C. albicans cell starvation despite sufficient nutrient availability in the medium; therefore, it can be speculated that SBTX blocks nutrient uptake systems. Because neither the starvation signal nor the alkaline response pathway lead to the induction of hyphae, we hypothesise that conflicting signals are transmitted to the complex regulatory network controlling morphogenesis, eventually preventing the filamentation signal from reaching a significant threshold.

Antifungal and other biological activities of two 2S albumin-homologous proteins against pathogenic fungi

The aim of this study was to determine whether 2S albumins from Passiflora edulis f. flavicarpa and Capsicum annuum seeds inhibit growth, induce plasma membrane permeabilization and induce endogenous production of nitric oxide in different pathogenic and non-pathogenic yeasts. The 2S albumin from P. flavicarpa (Pf-Alb) inhibited the growth of Kluyveromyces marxiannus, Candida albicans and Candida parapsilosis. The membranes of these yeast strains were permeabilized in the presence of Pf-Alb. The Pf-Alb also inhibited the glucose-stimulated acidification of the medium by Saccharomyces cerevisiae and C. albicans cells, which indicates a probable impairment of fungal metabolism because the inhibition of acidification occurred at various Pf-Alb concentrations and pre-incubation times. The 2S albumin from C. annuum (Ca-Alb) inhibited the growth of the yeasts K. marxiannus, C. tropicalis, C. albicans and S. cerevisiae. These yeast strains exhibited NO induction in the presence of Ca-Alb and displayed cellular agglomeration, elongated cells and the induction of pseudohyphae. Pf-Alb and Ca-Alb at various concentrations also inhibited the glucose-stimulated acidification of the medium by S. cerevisiae cells. Our results indicate that the ability of antimicrobial plant proteins such as 2S albumins to induce microbial inhibition could be an important factor in determining pathogen virulence. Therefore, 2S albumins might be targets for the design of new antifungal drugs.

Imbibition of soybean seeds in warm water results in the release of copious amounts of Bowman-Birk protease inhibitor, a putative anticarcinogenic agent

Protease inhibitors play a protective role against pathogenic microorganisms and herbivorous insects. The two predominant protease inhibitors of soybean seeds are the Kunitz trypsin inhibitor (KTI) and Bowman-Birk protease inhibitor (BBI). In this study, we report that soybean seeds incubated in warm water release large amounts of proteins into the surrounding media. Two-dimensional gel electrophoresis analysis of the seed exudates resulted in the separation of 93 distinct protein spots out of which 90 spots were identified by LC-MS/MS. The basic 7S globulin and the BBI are the two predominant proteins found in the soybean seed exudates. In addition to 7S and 11S seed storage proteins, others known to protect the seeds against pathogens and pests including KTI, peroxidase, α-galactosidase, and endo-1.3-β-glucanase were also identified in the seed exudates. Soybean seed exudate obtained by incubating the seeds in warm water was also able to inhibit the growth of human breast cancer cell line MCF-7. Since soybean seeds release large amounts of enzymatically active BBI when immersed in warm water, our procedure could be exploited as a simplified alternative method for the preparation of BBI concentrate which is being used as a cancer chemoprotective agent.

Plant storage proteins with antimicrobial activity: novel insights into plant defense mechanisms

Storage proteins perform essential roles in plant survival, acting as molecular reserves important for plant growth and maintenance, as well as being involved in defense mechanisms by virtue of their properties as insecticidal and antimicrobial proteins. These proteins accumulate in storage vacuoles inside plant cells, and, in response to determined signals, they may be used by the different plant tissues in response to pathogen attack. To shed some light on these remarkable proteins with dual functions, storage proteins found in germinative tissues, such as seeds and kernels, and in vegetative tissues, such as tubercles and leaves, are extensively discussed here, along with the related mechanisms of protein expression. Among these proteins, we focus on 2S albumins, Kunitz proteinase inhibitors, plant lectins, glycine-rich proteins, vicilins, patatins, tarins, and ocatins. Finally, the potential use of these molecules in development of drugs to combat human and plant pathogens, contributing to the development of new biotechnology-based medications and products for agribusiness, is also presented.

The role of plant defence proteins in fungal pathogenesis

SUMMARY It is becoming increasingly evident that a plant-pathogen interaction may be compared to an open warfare, whose major weapons are proteins synthesized by both organisms. These weapons were gradually developed in what must have been a multimillion-year evolutionary game of ping-pong. The outcome of each battle results in the establishment of resistance or pathogenesis. The plethora of resistance mechanisms exhibited by plants may be grouped into constitutive and inducible, and range from morphological to structural and chemical defences. Most of these mechanisms are defensive, exhibiting a passive role, but some are highly active against pathogens, using as major targets the fungal cell wall, the plasma membrane or intracellular targets. A considerable overlap exists between pathogenesis-related (PR) proteins and antifungal proteins. However, many of the now considered 17 families of PR proteins do not present any known role as antipathogen activity, whereas among the 13 classes of antifungal proteins, most are not PR proteins. Discovery of novel antifungal proteins and peptides continues at a rapid pace. In their long coevolution with plants, phytopathogens have evolved ways to avoid or circumvent the plant defence weaponry. These include protection of fungal structures from plant defence reactions, inhibition of elicitor-induced plant defence responses and suppression of plant defences. A detailed understanding of the molecular events that take place during a plant-pathogen interaction is an essential goal for disease control in the future.

The antifungal properties of a 2S albumin-homologous protein from passion fruit seeds involve plasma membrane permeabilization and ultrastructural alterations in yeast cells

Different types of antimicrobial proteins were purified from plant seeds, including chitinases, β-1,3-glucanases, defensins, thionins, lipid transfer proteins and 2S albumins. It has become clear that these groups of proteins play an important role in the protection of plants from microbial infection. Recent results from our laboratory have shown that the defense-related proteins from passion fruit seeds, named Pf1 and Pf2 (which show sequence homology with 2S albumins), inhibit fungal growth and glucose-stimulated acidification of the medium by Saccharomyces cerevisiae cells. The aim of this study was to determine whether 2S albumins from passion fruit seeds induce plasma membrane permeabilization and cause morphological alterations in yeast cells. Initially, we used an assay based on the uptake of SYTOX Green, an organic compound that fluoresces upon interaction with nucleic acids and penetrates cells with compromised plasma membranes, to investigate membrane permeabilization in S. cerevisiae cells. When viewed with a confocal laser microscope, S. cervisiae cells showed strong SYTOX Green fluorescence in the cytosol, especially in the nuclei. 2S albumins also inhibited glucose-stimulated acidification of the medium by S. cerevisiae cells, which indicates a probable impairment of fungal metabolism. The microscopical analysis of the yeast cells treated with 2S albumins demonstrated several morphological alterations in cell shape, cell surface, cell wall and bud formation, as well as in the organization of intracellular organelles.

Antimicrobial peptides from chilli pepper seeds causes yeast plasma membrane permeabilization and inhibits the acidification of the medium by yeast cells

During the last few years, a growing number of cysteine-rich antimicrobial peptides has been isolated from plants and particularly from seeds. It has become increasingly clear that these peptides play an important role in the protection of plants against microbial infection. In this work, proteins from chili pepper (Capsicum annuum L.) seeds were extracted in phosphate buffer, pH 5.4 and peptides purification were performed by employing ion-exchange chromatographies on DEAE, CM-Sepharose, Sephacryl S-100 and reverse phase in HPLC. Three peptide enriched fractions, namely F1, F2 and F3, were obtained after the CM-Sepharose chromatography. The F1 fraction, mainly composed of three peptides ranging from 6 to 10 kDa, was submitted to N-terminal amino acid sequencing. The closer to 10 kDa peptide showed high sequence homology to lipid transfer proteins (LTPs) previously isolated from others seeds. F1 fraction exhibited strong fungicidal activity against Candida albicans, Saccharomyces cerevisiae and Schizosaccharomyces pombe and also promoted several morphological changes to C. albicans, including the formation of pseudohyphae, as revealed by scanning electron micrography. F1 fraction also reduced the glucose stimulated acidification of the medium mediated by H(+)-ATPase of S. cerevisiae cells in a dose-dependent manner and caused the permeabilization of yeast plasma membrane to the dye SYTOX Green, as verified by confocal laser microscopy.

Purification and characterization of a novel peptide with antifungal activity from Bothrops jararaca venom

Different peptides have been isolated from a wide range of animal species. It is has become increasingly clear that due to the development of antibiotic-resistant microbes, antibacterial and antifungal peptides have attracted the attention in recent years, in order to find new therapeutic agents. In this work, a novel peptide with high inhibitory activity against fungi growth have been isolated from the venom of the Brazilian snake Bothrops jararaca. A Sephacryl S-100 gel filtration column was employed for further separation of proteins. The FV fraction with high antifungal activity was named Pep5Bj, pooled and submitted to reverse-phase chromatography in HPLC. The fraction containing the isolated peptide inhibited the growth of different phytopathogenic fungi (Fusarium oxysporum and Colletotrichum lindemuthianum) and yeast (Candida albicans and Saccharomyces cerevisiae). The peptide minimal inhibitory concentration is comparable to other known antifungal peptides, like insect defensins and cecropins, found in the last years in a large diversity of animals. We investigate F. oxysporum cells membrane permeabilization using SYTOX Green uptake, an organic compound that fluoresces upon interaction with nucleic acids after penetration in cell with compromised plasma membranes. When viewed under fluorescence optical microscopy, F. oxysporum cells exposed to Pep5Bj display strong SYTOX Green fluorescence in the cytosol, especially in the nuclei. The SYTOX Green data suggested that this effect is related to membrane permeabilization. The molecular masses of this peptide was obtained by MALDI-TOF spectrometry and corresponded to 1370Da.

A 2S albumin-homologous protein from passion fruit seeds inhibits the fungal growth and acidification of the medium by Fusarium oxysporum

Antimicrobial proteins have been isolated from a wide range of plant species. More recently, it has become increasingly clear that these types of proteins play an important role in the protection of plants. In this study, we investigate the presence of defense-related proteins from passion fruit (Passiflora edulis f. flavicarpa) seeds. Initially, seed flour was extracted for 2h (at 4 degrees C) with phosphate buffer, pH 5.5. The precipitate obtained between 0 and 70% relative ammonium sulfate saturation was re-dissolved in distilled water and heated at 80 degrees C for 15 min. The resulting suspension was clarified by centrifugation and the supernatant (F/0-70) was extensively dialyzed. A Sephadex G-50 size exclusion column was employed for further separation of proteins. The fraction with antifungal activity was pooled and submitted to CM-Sepharose cation exchange. Two proteins, named Pf1 and Pf2, were eluted in 0.1 and 0.2M of salt, respectively, and submitted to reverse-phase chromatography in HPLC. This fraction inhibited the growth, in an in vitro assay, of the phytopathogenic fungi Fusarium oxysporum and colletotrichum lindemuthianum and the yeast Saccharomyces cerevisiae and strongly inhibited glucose-stimulated acidification of the medium by F. oxysporum in a dose-dependent manner. The molecular masses of these proteins, referred to now as Pf1-RP and Pf2-RP, were obtained by MALDI-TOF spectrometry and corresponded to 12,088 Da for Pf1-RP and 11,930 Da for Pf2-RP. These proteins were also subjected to automated N-terminal amino acid sequencing. Sequence comparisons for the heavy subunit of Pf2-RP showed the presence of a protein with a high degree of homology to storage 2S albumins.

Temporal generation of multiple antifungal proteins in primed seeds

A drastic increase of antifungal activity was demonstrated during plant seed germination and in seed protein extract in vitro. Multiple antifungal proteins with a wide spectrum of activity were generated and identified. Chromatographic and electrophoretic analysis demonstrated that during seed germination, more fractions with potent antifungal activity were generated, and the antifungal activity shifted from small molecules to high molecular proteins. This germination-related increase of antifungal activity were observed in all three plants tested, i.e., cheeseweed, cigar tree and wheat. This rapid increase of antifungal activity was also observed with incubation of seed proteins in vitro, suggesting that at least part of the antifungal protein generation is independent of gene expression. Seven antifungal proteins with activities against five different plant pathogens were isolated from the active fractions. However, random digestion of purified seed protein with multiple proteinases failed to generate any antifungal proteins. It is suggested that during plant seed germination, a regulated biochemical process takes place that results in the generation of multiple peptides or proteins with antifungal activities. This onset of antifungal proteins is transitional in nature, but could play an important role in the protection of plants in early stage of development when the more sophisticated defense system has yet to develop.

Potent heterologous antifungal proteins from cheeseweed (Malva parviflora)

Two novel antifungal proteins were purified and characterized from cheeseweed (Malva parviflora). Both proteins, designated CW-1 and CW-2, are composed of two different subunits of 5000 and 3000 Da, respectively. These proteins possess very potent antifungal activities, and more interestingly the inhibition is fungicidal instead of fungistatic. At low salt condition, the IC(50) of CW-1 and CW-2 against Fusarium graminearum (Fg) is 2.5 ppm. At high salt condition which diminishes the antifungal activity of many antifungal proteins, both CW-1 and CW-2 still maintain potent activity against Fg with IC(50) of 10 ppm. The two subunits could be separated by gel filtration in the presence of 6 M urea, but their antifungal activity cannot be recovered after the removal of urea. Amino acid sequence analysis indicates that both subunits of CW-1 show homology to 2S albumin, whereas the two subunits of CW-2 have homology to vicilin protein from cotton. To our knowledge, this is the first report of isolation and characterization of heterologous antifungal proteins from any source.

Microbial relatives of the seed storage proteins of higher plants: conservation of structure and diversification of function during evolution of the cupin superfamily

This review summarizes the recent discovery of the cupin superfamily (from the Latin term "cupa," a small barrel) of functionally diverse proteins that initially were limited to several higher plant proteins such as seed storage proteins, germin (an oxalate oxidase), germin-like proteins, and auxin-binding protein. Knowledge of the three-dimensional structure of two vicilins, seed proteins with a characteristic beta-barrel core, led to the identification of a small number of conserved residues and thence to the discovery of several microbial proteins which share these key amino acids. In particular, there is a highly conserved pattern of two histidine-containing motifs with a varied intermotif spacing. This cupin signature is found as a central component of many microbial proteins including certain types of phosphomannose isomerase, polyketide synthase, epimerase, and dioxygenase. In addition, the signature has been identified within the N-terminal effector domain in a subgroup of bacterial AraC transcription factors. As well as these single-domain cupins, this survey has identified other classes of two-domain bicupins including bacterial gentisate 1, 2-dioxygenases and 1-hydroxy-2-naphthoate dioxygenases, fungal oxalate decarboxylases, and legume sucrose-binding proteins. Cupin evolution is discussed from the perspective of the structure-function relationships, using data from the genomes of several prokaryotes, especially Bacillus subtilis. Many of these functions involve aspects of sugar metabolism and cell wall synthesis and are concerned with responses to abiotic stress such as heat, desiccation, or starvation. Particular emphasis is also given to the oxalate-degrading enzymes from microbes, their biological significance, and their value in a range of medical and other applications.