Alternaria alternata NADP-dependent mannitol dehydrogenase is an important fungal allergen

BACKGROUND

Alternaria alternata is one of the most important allergenic fungi worldwide. Mannitol dehydrogenase (MtDH) has previously been shown to be a major allergen of Cladosporium herbarum and cross-reactivity has been demonstrated for several fungal allergens.

OBJECTIVE

The present study's objective was to clone the MtDH from an A. alternata cDNA library, express and purify the recombinant non-fusion protein and test its IgE-binding properties. Methods A cDNA library prepared from A. alternata hyphae and spores was screened for mannitol dehydrogenase by DNA hybridization with the radioactively labelled C. herbarum homologue as a probe. The resulting clone was sequenced and heterologously expressed in Escherichia coli as a recombinant non-fusion protein, which was purified to homogeneity and analysed for its IgE-binding capacity.

RESULTS

The coding sequence of the full-length cDNA clone comprises 798 bp encoding a protein with a molecular mass of 28.6 kDa and a predicted pI of 5.88. Protein sequence analysis revealed an identity of 75% and a homology of 86% between the MtDHs of A. alternata and C. herbarum. The functional mannitol dehydrogenase was expressed in the E. coli strain BL21(DE3) transformed with the vector pMW172 and purified to homogeneity. The enzyme catalyses the NADPH-dependent conversion of d-fructose to d-mannitol. In IgE-ELISA and immunoblots, MtDH is recognized by 41% of A. alternata-allergic patients. In vivo immunoreactivity of the recombinant MtDH was verified by skin prick testing. Finally, inhibition-ELISA experiments confirmed cross-reactivity between the MtDHs of A. alternata and C. herbarum.

CONCLUSION

Mannitol dehydrogenase (Alt a 8) represents an important new allergen of the ascomycete A. alternata that might be suitable for improving diagnostic and therapeutic procedures.

GermOnline, a cross-species community knowledgebase on germ cell differentiation

GermOnline provides information and microarray expression data for genes involved in mitosis and meiosis, gamete formation and germ line development across species. The database has been developed, and is being curated and updated, by life scientists in cooperation with bioinformaticists. Information is contributed through an online form using free text, images and the controlled vocabulary developed by the GeneOntology Consortium. Authors provide up to three references in support of their contribution. The database is governed by an international board of scientists to ensure a standardized data format and the highest quality of GermOnline's information content. Release 2.0 provides exclusive access to microarray expression data from Saccharomyces cerevisiae and Rattus norvegicus, as well as curated information on approximately 700 genes from various organisms. The locus report pages include links to external databases that contain relevant annotation, microarray expression and proteome data. Conversely, the Saccharomyces Genome Database (SGD), S.cerevisiae GeneDB and Swiss-Prot link to the budding yeast section of GermOnline from their respective locus pages. GermOnline, a fully operational prototype subject-oriented knowledgebase designed for community annotation and array data visualization, is accessible at http://www.germonline.org. The target audience includes researchers who work on mitotic cell division, meiosis, gametogenesis, germ line development, human reproductive health and comparative genomics.

Sensitization to fungi: epidemiology, comparative skin tests, and IgE reactivity of fungal extracts

BACKGROUND

Several fungal species are known to cause severe respiratory and cutaneous allergic diseases. Extracts from several allergenic fungi are used for in vivo and in vitro tests, as standard preparations are still not available.

OBJECTIVE

The aims are to define the pattern of in vivo and in vitro IgE reactivity to fungal species in an allergic population with respiratory symptoms; to determine the influence of different extract preparations on diagnostic results; and to evaluate whether there exists a relationship between the diagnostic pattern of reactivity and the pattern of specific IgE reactivity in immunoblots.

METHODS

Skin prick tests were applied to a cohort of 4962 respiratory subjects, aged 3-80 years. Fungal extracts from Alternaria, Aspergillus, Candida, Cladosporium, Penicillium, Saccharomyces, and Trichophyton were used, along with extracts from pollens, mites, and animal dander. Demographical and diagnostic data were recorded. IgE detection was carried out with the same allergenic extracts plus Malassezia. Comparative skin tests and IgE detection were carried out using extracts from three commercial suppliers. IgE immunoblots were carried out with the same panel of commercial fungal extracts and were compared with in-house extracts. Data analysis was carried out by grouping the population on the basis of their reactivity to a single, to two or to more than two, mould species.

RESULTS

Nineteen percent of the allergic population reacted to at least one fungal extract by means of the skin test. Alternaria and Candida accounted for the largest number of positive tests, and along with Trichophyton they were the main sensitizers in the subset of patients with an isolated sensitization. The prevalence of skin test reactivity increased for these three fungi in the subsets with two associated reactivities and, furthermore, in the subset showing reactivity to more than two mould species. In the latter group, a steady increase of the skin test reactivity was recorded for all the other fungal sources, suggesting a clustered reactivity. Comparative skin and IgE testing with different groups of subjects with a simple pattern of skin reactivity resulted in sensitivity differences between in vivo and in vitro tests, whereas discrepant results were recorded in the subsets of patients with multiple fungi sensitization. Although hampered by the limited reliability of fungal extracts, IgE immunoblots revealed differing patterns of reactivity when sera from the three subsets were used. This suggests a link between the diagnostic reactivity pattern and the IgE sensitization to extracts' components. Age and gender distribution differed among the Alternaria-, Candida-, and Trichophyton-sensitized subjects, but not in the subset with more than two fungi sensitizations.

CONCLUSIONS

The preliminary assessment of a new classification of the mould-sensitized population has been reached. The limiting quality of fungal extracts requires future studies using an allergenic molecule-based approach. The diagnostic process and the definition of the reactivity pattern would thus be easy, and it could lead to a novel specific immunotherapy approach.

Nuclear transport factor 2 represents a novel cross-reactive fungal allergen

BACKGROUND

Ubiquitously occuring moulds are important allergenic sources known to elicit IgE-mediated allergic diseases and to share cross-reactive allergens. Limited information is available about the molecular structures involved in cross-reactivity. We aimed to clone and characterize cross-reactive mould allergens.

METHODS

Phage surface-displayed Alternaria alternata and Cladosporium herbarum cDNA libraries were screened using sera from Aspergillus fumigatus-sensitized patients. Inserts encoding putative allergens were sequenced, and recombinant proteins used to demonstrate cross-reactivity by inhibition experiments and skin test. Three-dimensional homology models of cloned putative nuclear transport factor 2 (NTF2) were constructed based on known NTF2 structure to corroborate the functional and structural properties of the novel allergens.

RESULTS

After six rounds of affinity selection, the libraries were enriched for clones displaying allergens. Sequencing of inserts showed that some clones derived from Alternaria alternata and Cladosporium herbarum contain open reading frames predicting proteins of 124 and 125 amino acids corresponding to NTF2. The recombinant proteins were able to bind and cross-inhibit IgE binding and to elicit type I skin reactions in mould-sensitized individuals, demonstrating the allergenicity of the proteins.

CONCLUSIONS

NTF2 represents a novel cross-reactive fungal allergen as demonstrated by sequence homology, three-dimensional modelling, inhibition experiments and skin test reactivity.

The nucle(ol)ar Tif6p and Efl1p are required for a late cytoplasmic step of ribosome synthesis

Deletion of elongation factor-like 1 (Efl1p), a cytoplasmic GTPase homologous to the ribosomal translocases EF-G/EF-2, results in nucle(ol)ar pre-rRNA processing and pre-60S subunits export defects. Efl1p interacts genetically with Tif6p, a nucle(ol)ar protein stably associated with pre-60S subunits and required for their synthesis and nuclear exit. In the absence of Efl1p, 50% of Tif6p is relocated to the cytoplasm. In vitro, the GTPase activity of Efl1p is stimulated by 60S, and Efl1p promotes the dissociation of Tif6p-60S complexes. We propose that Tif6p binds to the pre-60S subunits in the nucle(ol)us and escorts them to the cytoplasm where the GTPase activity of Efl1p triggers a late structural rearrangement, which facilitates the release of Tif6p and its recycling to the nucle(ol)us.

Brix from xenopus laevis and brx1p from yeast define a new family of proteins involved in the biogenesis of large ribosomal subunits

A clone was isolated from a cDNA library from early embryos of Xenopus laevis that codes for a highly charged protein containing 339 amino acids. Two putative nuclear localization signals could be identified in its sequence, but no other known motifs or domains. Closely related ORFs are present in the genomes of man, C. elegans, yeast and Arabidopsis. A fusion protein with GFP expressed in HeLa cells or Xenopus oocytes was found to be localized in the nucleolus and coiled (Cajal) bodies. Moreover, immunoprecipitation experiments demonstrated that the new Xenopus protein interacts with 5S, 5.8S and 28S RNAs of large ribosomal subunits. The name Brix (biogenesis of ribosomes in Xenopus) is proposed for this protein and the corresponding gene. In Saccharomyces cerevisiae, the essential gene YOL077c, now named BRX1, codes for the Brix homolog, which is also localized in the nucleolus. Depletion of Brx1 p in a conditional yeast mutant leads to defects in rRNA processing, and a block in the assembly of large ribosomal subunits.

Somatic diversity of the immunoglobulin repertoire is controlled in an isotype-specific manner

We have studied two aspects of the IgE immune response. First, we have compared the kinetics of the IgE response to the T cell-dependent antigen ph-Ox coupled to ovalbumin with that of the IgG1 response and we have assessed the quality of the IgE response. Second, we have studied the generation of somatic diversity, understood as the combined effect of somatic mutation and the selection of D(iversity) and J(oining) elements, in germinal center B cells at the molecular level, using the germ-line sequence of the prototype anti-ph-Ox heavy chain variable element V(H)Ox1 as reference. We evaluated sequences derived from mu-, gamma 1- and epsilon-variable elements and showed that somatic diversification was different for all isotypes studied. We further compared the IgE responses of wild-type mice with those of mice expressing a truncated cytoplasmic IgE tail (IgE(KVK Delta tail)). IgE(KVK Delta tail) mice showed a more diverse sequence pattern. We corroborated previous results suggesting that short CDR3 regions are indicative for high-affinity antibodies by measuring relative affinities of phage-expressed Fab fragments with prototype long and short CDR3 regions. Therefore, the composition of the antigen-receptor is responsible for the selection process and the expansion of antigen-specific cells, leading to an isotype-specific antibody repertoire.

Quantitation of the major fungal allergens, Alt a 1 and Asp f 1, in commercial allergenic products

BACKGROUND

Alternaria is one of the most important fungi associated with allergic disease, whereas Aspergillus fumigatus is involved in a broad spectrum of pulmonary diseases. Currently, fungal extracts used for diagnosis in the United States are unstandardized, and their allergenic content cannot be compared directly.

OBJECTIVE

The goal of this study was to compare the variability of major allergen levels among US allergenic products derived from fungi: specifically, Alt a 1 levels in Alternaria alternata extracts, and Asp f 1 levels in A fumigatus extracts.

METHODS

A novel 2-site monoclonal antibody ELISA was used for measuring Alt a 1 using recombinant Alt a 1 as a standard. Asp f 1 was also measured by ELISA. Allergenic products produced by 8 US manufacturers over a 2-year period were compared, as were multiple lots produced by a single company.

RESULTS

Alt a 1 levels in Alternaria extracts from 8 companies produced in 1998 and 1999 ranged from less than 0.01 to 6.09 microg/mL (mean 1.4 +/- 1.6 microg/mL, n = 15). In general, Alt a 1 levels were consistent within and between companies (1.4 +/- 1.1 microg/mL, n = 27), with 21 of 32 (66%) of all extracts tested containing 0.7 to 2 microg/mL Alt a 1. Aspergillus extracts showed much greater variability in Asp f 1 levels, with extracts from 8 companies containing from less than 0.1 to 64 microg/mL Asp f 1 (mean 16.3 +/- 23.9 microg/mL, n = 15). Overall variability was greater for Aspergillus products within and between manufacturers (22 +/- 22 microg/mL Asp f 1, n = 20).

CONCLUSIONS

ELISA-based assays for specific allergens showed greater consistency among allergenic products derived from Alternaria than from Aspergillus. These assays should facilitate improved quality control and standardization of fungal allergen extracts and lead to the development of more consistent products for clinical use.

Aged mother cells of Saccharomyces cerevisiae show markers of oxidative stress and apoptosis

Recently, we and others have shown that genetic and environmental changes that increase the load of yeast cells with reactive oxygen species (ROS) lead to a shortening of the life span of yeast mother cells. Deletions of yeast genes coding for the superoxide dismutases or the catalases, as well as changes in atmospheric oxygen concentration, considerably shortened the life span. The presence of the physiological antioxidant glutathione, on the other hand, increased the life span of yeast cells. Taken together, these results pointed to a role for oxygen in the yeast ageing process. Here, we show by staining with dihydrorhodamine that old yeast mother cells isolated by elutriation, but not young cells, contain ROS that are localized in the mitochondria. A relatively large proportion of the old mother cells shows phenotypic markers of yeast apoptosis, i.e. TUNEL (TdT-mediated dUTP nick end labelling) and annexin V staining. Although it has been shown previously that apoptosis in yeast can be induced by a cdc48 allele, by expressing pro-apoptotic human cDNAs or by stressing the cells with hydrogen peroxide, we are now showing a physiological role for apoptosis in unstressed but aged wild-type yeast mother cells.

The IgE antigen receptor: a key regulator for the production of IgE antibodies

Immunoglobulins in general form a substantial component of serum proteins, and play a role in homeostatic mechanisms, a first line of defense against pathogenic organisms and in immunological memory. In the secreted form, immunoglobulins represent the effector arm of the humoral immune system. However, immunoglobulins are not only secreted, but can also be expressed on the surface of a B lymphocyte (membrane immunoglobulin), and, in this physical state, most likely convey signals to steer the B cell along its differentiation pathway. A step forward in the understanding of the role of membrane immunoglobulins other than membrane IgM or IgD was achieved with two mouse lines with mutations in the epsilon heavy chain gene. In IgE(DeltaM1M2) mice serum IgE is reduced to less than 10% of normal mice, while IgE(KVKDeltatail) mice show a reduction of 50%, reflecting a serious impairment of the IgE-mediated immune response. We think that the cytoplasmic tail of IgE is involved in a signal transduction which leads to the expression of high quantities and qualities of secreted IgE immunoglobulins.

IgE-binding epitopes of enolases, a class of highly conserved fungal allergens

BACKGROUND

Cladosporium herbarum and Alternaria alternata are two of the most prominent fungal species inducing type I allergy. Previously, we have demonstrated that enolase (Cla h 6) is the second most important allergen of C herbarum in terms of frequency of sensitization.

OBJECTIVE

IgE-reactive B-cell epitopes of C herbarum enolase were analyzed, and cross-reactivity between fungal enolases was investigated.

METHODS

Cla h 6 glutathione-S-transferase fusion peptides were constructed by means of PCR cloning. A alternata enolase (Alt a 5) was isolated by screening a complementary (c)DNA expression library with a C herbarum enolase DNA probe.

RESULTS

Mapping of Cla h 6 IgE-binding epitopes identified a peptide with a length of 69 amino acids (peptide 9), which bound IgE from 8 of 8 patients. Analysis of the conformation of peptide 9 revealed that it does not form a compact structure but rather spans the whole length of the protein, with side chains exposed to solvent at 3 locations. Peptide 9 in the context of Escherichia coli glutathione-S-transferase not only binds IgE but also competitively inhibits IgE binding to Alt a 5. This result indicates that the epitope or epitopes on peptide 9 constitute a major cross-reacting epitope or epitopes on the enolases from C herbarum and A alternata in the case of the one patient tested.

CONCLUSIONS

We demonstrated that the glycolytic enzyme enolase is an allergen not only in C herbarum but also in A alternata. Additionally, enolase was shown to exhibit high cross-reactivity to other fungal enolases. On the basis of the results presented here, we propose the use of recombinant Cla h 6 or maybe even peptide 9 of Cla h 6 for diagnosis and possibly therapy of mold allergy.

The influence of oxygen toxicity on yeast mother cell-specific aging

The effect of deleting both catalase genes and of increased oxygen as well as paraquat (a pro-oxidant) on the replicative life span of yeast mother cells has been investigated to test the so-called oxygen theory of aging. This is well established in higher organisms, but has not been extensively tested in the unicellular yeast model system. Life span determinations were performed in ambient air or in a controlled atmosphere (55% oxygen) and an isogenic series of strains deleted for one or both yeast catalases was used and compared with wild type. In the absence of cellular catalase, increased oxygen caused a marked decrease in life span that could be completely reversed by adding 1 mM GSH, a physiological antioxidant, to the yeast growth medium. In a second unrelated strain, the effects were similar although even the wild type showed a decrease in life span when oxygen was increased. The effect could again be compensated by addition of extracellular GSH. Our results show that manipulating the detoxification of reactive oxygen species has a profound effect on yeast aging. These findings are discussed in the light of recent results relating to oxygen toxicity in the aging process of higher organisms.

Ultrasonic transmission in viscoelastic substances

PURPOSE

To study the propagation of ultrasonic shock waves in viscoelastic agents and the resulting corneal load.

SETTING

University Siegen, Institute for Mechanics and Control Engineering, Siegen, Germany.

METHODS

The anterior chamber of a manufactured artificial eye was constructed according to anatomic dimensions. Three openings were drilled--for the phaco tip, for the exchange of a viscoelastic agent or water, and for the shock-wave sensor. The sensor was fixed to the area corresponding to the corneal apex. The sensor signal was analyzed using a direct oscilloscope that measured the amplitude reaching the corneal apex. Shock-wave propagation in several viscoelastic agents was compared with that in balanced salt solution.

RESULTS

In hydroxypropyl methylcellulose, the shock wave was amplified or influenced slightly. In hyaluronic-acid preparations, acoustic dampening occurred.

CONCLUSION

Removal of hyaluronic-acid derivatives prior to phacoemulsification is not necessary.

Improvement of the immune response against plasmid DNA encoding OspC of Borrelia by an ER-targeting leader sequence

The present study outlines the characterization of a DNA-based immune response against the OspC antigen, one of the most promising candidates for a Borrelia vaccine. Balb/c mice were injected intradermally with plasmid DNA encoding the OspC gene (lacking the natural leader sequence) under transcriptional control of the cytomegalovirus (CMV) promotor. Immunization with this construct elicited only a marginal response, which was drastically improved by a fusion construct containing the human tissue plasminogen activator (hTPA) signal sequence. The results indicate that for DNA-based immunization against OspC an ER-targeting signal may be necessary for both antibody production as well as cellular immune responses.

Reduced in vivo allergenicity of Bet v 1d isoform, a natural component of birch pollen

BACKGROUND

The major allergen of birch pollen, Bet v 1, is present in structurally slightly different isoforms. It has been postulated that certain isoforms show a distinct ability to bind birch pollen-specific IgE, although the T-cell response remains similar.

OBJECTIVE

We verified the hypothesis of a distinct allergenicity but similar T-cell immunogenicity of 2 isoforms in birch pollen-allergic subjects by in vivo tests and an in vitro assay for T-cell stimulation.

METHODS

Forty-eight birch pollen-allergic, 11 grass pollen-allergic, and 10 nonatopic control individuals were tested with 10-fold increasing concentrations (0.01 to 10.0 microg/mL) of recombinant (r) Bet v 1a and rBet v 1d by skin prick test (SPT), intradermal test (IDT), and conjunctival provocation test (CPT). An allergen-specific proliferation assay was performed on 21 patients with the 2 recombinant and the natural birch pollen allergens.

RESULTS

In each test system only birch pollen-allergic subjects but no controls reacted to the recombinant allergens. A positive in vivo response to 10 microg/mL of rBet v 1a was observed in 21 of 48 by SPT, in 48 of 48 by IDT, and in 33 of 48 by CPT. In contrast, the IDT response to 10 microg/mL of rBet v 1d was reduced by a factor of 100 because it was equivalent to the response to 0.1 microg/mL of rBet v 1a. rBet v 1d failed to elicit a positive reaction in SPT and CPT. The proliferative response of T cells was similar for both recombinant isoforms because 8 of 21 individuals reacted to rBet v 1a and 6 of 21 to rBet v 1d. Only 1 subject had a positive reaction to rBet v 1d alone.

CONCLUSION

The natural isoforms rBet v 1a and rBet v 1d differ in their ability to bind IgE but are similar in their immunogenicity for T cells. Thus rBet v 1d might be a promising candidate for use in immunotherapy of birch pollen-allergic individuals.

Heterologous expression, purification, and kinetic comparison of the cytoplasmic and mitochondrial glyoxalase II enzymes, Glo2p and Glo4p, from Saccharomyces cerevisiae

The aims of the present study are (i) to purify a mitochondrial glyoxalase II to homogeneity for the first time from any organism and (ii) to compare its kinetic properties with those of the cytoplasmic enzyme. Both the cytoplasmic and the mitochondrial glyoxalases II from Saccharomyces cerevisiae, which are the products of two distinct genes, GLO2 and GLO4, were purified from yeast and in recombinant form from Escherichia coli. To obtain a higher protein yield (compared to wild-type expression) in yeast, the genes were placed under the control of the strong GAL1 promoter on a multicopy plasmid. Amino-terminal sequencing and molecular mass determination by MALDI-TOF mass spectrometry of the mitochondrial Glo4 protein revealed Met-11 of the primary translation product of the gene as the N-terminal amino acid. Judged by enzyme kinetic properties the recombinant and natural proteins were equivalent. The cytoplasmic and the mitochondrial enzyme differed in the pH dependence of the kinetic parameters for the main substrate, S-d-lactoylglutathione. Whereas the cytoplasmic protein showed a pronounced peak of enzyme activity between pH 7-8 and a continuous up to fivefold increase of the K(M) value with increasing pH (from 5. 5-9.0), the mitochondrial protein had a nearly constant K(M) value and an activity maximum over a broad pH range (6.5-9.0). The kinetic parameters (at pH 7.5) of both the cytoplasmic and the mitochondrial enzyme for S-D-lactoylglutathione were of the same order of magnitude as reported recently for the human and Arabidopsis thaliana enzymes which are presumably of cytoplasmic origin. However, both yeast enzymes showed a severalfold lower preference for the more hydrophobic substrate, S-d-mandeloylglutathione.

Humoral and cell-mediated autoimmune reactions to human acidic ribosomal P2 protein in individuals sensitized to Aspergillus fumigatus P2 protein

A panel of cDNAs encoding allergenic proteins was isolated from an Aspergillus fumigatus cDNA library displayed on the surface of filamentous phage. Solid phase-immobilized serum immunoglobulin E (IgE) from A. fumigatus-allergic individuals was used to enrich phage displaying IgE-binding molecules. One of the cDNAs encoded a 11.1-kD protein that was identified as acidic ribosomal phosphoprotein type 2 (P2 protein). The allergen, formally termed rAsp f 8, shares >62% sequence identity and >84% sequence homology to corresponding eukaryotic P2 proteins, including human P2 protein. The sequences encoding human and fungal P2 protein were subcloned, expressed in Escherichia coli as His6-tagged fusion proteins, and purified by Ni2+-chelate affinity chromatography. Both recombinant P2 proteins were recognized by IgE antibodies from allergic individuals sensitized to the A. fumigatus P2 protein and elicited strong type 1-specific skin reactions in these individuals. Moreover, human and fungal P2 proteins induced proliferative responses in peripheral blood mononuclear cells of A. fumigatus- allergic subjects sensitized to the fungal P2 protein. These data provide strong evidence for in vitro and in vivo humoral and cell-mediated autoreactivity to human P2 protein in patients suffering from chronic A. fumigatus allergy.

The importance of recombinant allergens for diagnosis and therapy of IgE-mediated allergies

In the past 10 years, a considerable number of cDNAs coding for allergens have been isolated and expressed. Intensive investigations showed that recombinant allergens and their respective natural counterparts possess comparable properties with respect to structure, function and interaction with the immune system. Recent studies documented that in vitro as well as in vivo diagnosis of IgE-mediated allergic diseases can be successfully improved by the application of recombinant allergens. In addition, new strategies for a safer specific immunotherapy (SIT) have been developed based on the knowledge of the primary structures of allergens. Naturally occurring isoforms of allergens as well as recombinant allergens with modified amino acid sequences show very low IgE binding capacity but strong T cell-stimulatory activity and represent possible candidates. In case of Bet v 1, the major birch pollen allergen, isoforms d, g and l and a Bet v 1a mutant, produced by site-directed mutagenesis resulting in 6 amino acid exchanges, fulfilled the above mentioned criteria. In a third approach, two adjacent peptides covering the entire Bet v 1a sequence were produced in an Escherichia coli expression system. These peptides contained most of the relevant T cell epitopes, but lost their IgE binding capacity and, thus, their ability to activate mast cells and basophils of sensitized patients. Our results suggest that allergen variants (isoforms, mutants, T cell epitope-containing peptides) may be used as 'hypoallergenic agents' in SIT.

GRC5 and NMD3 function in translational control of gene expression and interact genetically

The yeast gene, GRC5 (growth control), is a member of the highly conserved QM gene family, the human member of which has been associated with the suppression of Wilms' tumor. GRC5 encodes ribosomal protein L10, which is thought to play a regulatory role in the translational control of gene expression. A revertant screen identified four spontaneous revertants of the mutant grc5-1ts allele. Genetic and phenotypic analysis showed that these represent one gene, NMD3, and that the interaction of NMD3 and GRC5 is gene-specific. NMD3 was previously identified as a component of the nonsense-mediated mRNA decay pathway. The point mutations within NMD3 reported here may define a domain important for the functional interaction of Grc5p and Nmd3p.

Sporulation-specific expression of the yeast DIT1/DIT2 promoter is controlled by a newly identified repressor element and the short form of Rim101p

Expression of the yeast genes DIT1 and DIT2 is confined to mid/late sporulation. Transcription of these two divergently arranged genes is controlled by a common 900-bp intergenic region. Random mutagenesis of this promoter and tests with appropriate reporter constructs identified an 11-bp cis-acting palindromic sequence, DIT repressor element (DRE), as a major negative regulatory site during vegetative growth. Repression is exerted by DRE in conjunction with a mid-sporulation element (MSE)-like sequence situated 26 bp away. These sequence elements are both contained within the 76-bp negative regulatory element (NRE) defined previously [Friesen H., Hepworth, S. R. & Segall, J. (1997) Mol. Cell. Biol. 17, 123-134]. The activated form of Rim101p, a transcriptional inducer of the early meiotic gene IME1, enhances expression from the DIT1 promoter both in vegetative and sporulating cells. Activation by Rim101p does not seem to involve binding of Rim101p at either of the two cis-acting sites described here, since reporter constructs with both elements or most of the NRE deleted could still be activated by the short form of Rim101p.

Modulation of IgE reactivity of allergens by site-directed mutagenesis: potential use of hypoallergenic variants for immunotherapy

Specific immunotherapy is an efficient treatment for patients suffering from type I allergy. The mechanisms underlying successful immunotherapy are assumed to operate at the level of T helper cells, leading to a modulation of the immune response to allergens. During immunotherapy, increasing doses of allergens are given on a regular basis, and the beneficial effects for the patient depend on the concentration of allergen used. On the other hand, the risk of IgE-mediated anaphylactic side effects also increase with the amount of allergen applied per injection. Therefore, we have proposed the use of hypoallergenic (low IgE binding activity) forms of allergens for immunotherapy. We evaluated by site-directed mutagenesis the contributions of individual amino acid residues/positions for IgE binding to Bet v 1, the major allergen of birch pollen. We found that IgE binding to Bet v 1 depended on at least six amino acid residues/positions. Immunoblot analyses and inhibition experiments showed that the multiple-point Bet v 1 mutant exhibited extremely low reactivity with serum IgE from birch pollen-allergic patients. In vivo (skin prick) tests showed that the potency of the multiple-point mutant to induce typical urticarial type I reactions in pollen-allergic patients was significantly lower than for wild-type Bet v 1. Proliferation assays of allergen-specific T cell clones demonstrated that these six amino acid exchanges in the Bet v 1 sequence did not influence T cell recognition. Thus, the Bet v 1 six-point mutant displayed significantly reduced IgE binding activity, but conserved T cell activating capacity, which is necessary for immunomodulation. The approach described here may be generally applied to produce allergen variants to be used in a safe therapy form of immediate-type allergies.

Immunological and biological properties of Bet v 4, a novel birch pollen allergen with two EF-hand calcium-binding domains

We have isolated a cDNA clone coding for a birch pollen allergen, Bet v 4. The deduced amino acid sequence of Bet v 4 contained two typical EF-hand calcium-binding domains. Sequence similarities of Bet v 4 to calmodulin are primarily confined to the calcium-binding domains. However, significant sequence similarities extending outside the Ca2+-binding sites were found with a recently described group of pollen-specific allergens of Brassica and Bermuda grass. Both EF-hand domains of Bet v 4 are able to bind Ca2+, as demonstrated by 45Ca2+ blot overlay of wild type and calcium-binding deficient mutants of Bet v 4. Among pollen-allergic patients, protein-bound Ca2+ was not an absolute requirement for IgE recognition of Bet v 4. However, disruption of the carboxyl-terminal Ca2+-binding domain indicated that most IgE antibodies from allergic patients are directed against this site. IgE inhibition experiments suggested that Bet v 4 represents a highly cross-reactive pollen allergen. Pre-absorption of allergic sera with Bet v 4 drastically reduced IgE binding to proteins of similar molecular weight in pollen extracts from distantly related plant species (e.g. timothy grass, mugwort, lily) but not in extracts from plant-derived foodstuff. To test for a possible biological role in pollen germination and tube growth, we introduced recombinant Bet v 4 protein into growing lily pollen tubes by iontophoresis. As a result, cytoplasmic streaming stopped in the vicinity of the electrode tip, and a slight depolarization of the membrane voltage was measured. These effects were not observed with Ca2+-binding deficient mutants of Bet v 4. Thus, Bet v 4 and homologous proteins represent a new class of pollen-specific Ca2+-binding allergens that may have a physiological role as inhibitors of cytoplasmic streaming in outgrowing pollen tubes.

Validation of a youth/adolescent food frequency questionnaire

BACKGROUND

To address limited longitudinal nutrition data on children and adolescents, a self-administered food frequency questionnaire was designed for older children and adolescents. Initially, the Youth/Adolescent Questionnaire (YAQ) was developed and demonstrated to be reproducible. This study was conducted to evaluate its validity.

METHODS

The form was administered twice to a sample of 261 youths (ages 9 to 18) at an approximate interval of 1 year (1993-1994), and three 24-hr dietary recalls were collected during this period. Pearson correlation coefficients were calculated on nutrient data.

RESULTS

Validity was first evaluated by comparing the average of the three 24-hr recalls to the average of the two YAQs. Similar mean nutrients were found by both methods. Correlation coefficients between the mean energy-adjusted nutrients computed by the two methods ranged from 0.21 for sodium to 0.58 for folate. After correction for within-person error, the average correlation coefficient was 0.54, similar to that found among adults.

CONCLUSION

A simple self-administered questionnaire completed by older children and adolescents can provide nutritional information about this age group.

Identification and phenotypic analysis of two glyoxalase II encoding genes from Saccharomyces cerevisiae, GLO2 and GLO4, and intracellular localization of the corresponding proteins

We have isolated and characterized two genes coding for the glyoxalase II enzyme from Saccharomyces cerevisiae. The coding region of the GLO2 gene corresponds to a protein with 274 amino acids and a molecular mass of 31,306 daltons. The open reading frame of the GLO4 gene could be translated into a protein with 285 amino acids and a molecular mass of 32,325 daltons. The amino acid sequences of the deduced proteins are 59.1% identical and show high similarities to the sequence of the human glyoxalase II. When grown on either glucose or glycerol as a carbon source, a glo2 glo4 double deletion strain contains no glyoxalase II activity at all and shows no obvious phenotype during vegetative growth. However, this strain showed a similar high sensitivity against exogenous methylglyoxal as compared with a glyoxalase I-deficient strain. Whereas the GLO2 gene is expressed on both glucose and glycerol, the GLO4 gene is only active on glycerol. The active Glo2p protein is localized in the cytoplasm and the active Glo4p in the mitochondrial matrix. Heterologous expression of the full-length GLO2 coding region in Escherichia coli resulted in an active protein. However, to get an active Glo4p protein in E. coli, the putative mitochondrial transit peptide at the N-terminal end had to be removed by shortening the 5' end of the GLO4 open reading frame.

Phytopathogenic filamentous (Ashbya, Eremothecium) and dimorphic fungi (Holleya, Nematospora) with needle-shaped ascospores as new members within the Saccharomycetaceae

Phylogenetic relationships between species from the genera Kluyveromyces and Saccharomyces and representatives of the Metschnikowiaceae (Holleya, Metschnikowia, Nematospora) including the two filamentous phytopathogenic fungi Ashbya gossypii and Eremothecium ashbyii were studied by comparing the monosaccharide pattern of purified cell walls, the ubiquinone system, the presence of dityrosine in ascospore walls, and nucleotide sequences of ribosomal DNA (complete 18S rDNA, ITS1 and ITS2 region). Based on sequence information from both ITS regions, the genera Ashbya, Eremothecium, Holleya and Nematospora are closely related and may be placed in a single genus as suggested by Kurtzman (1995; J Industr. Microbiol. 14, 523-530). In a phylogenetic tree derived from the ITS1 and ITS2 region as well as in a tree derived from the complete 18S rDNA gene, the genus Metschnikowia remains distinct. The molecular evidence from ribosomal sequences suggests that morphology and ornamentation of ascospores as well as mycelium formation and fermentation should not be used as differentiating characters in family delimitation. Our data on cell wall sugars, ubiquinone side chains, dityrosine, and ribosomal DNA sequences support the inclusion of plant pathogenic, predominantly filamentous genera like Ashbya and Eremothecium or dimorphic genera like Holleya and Nematospora with needle-shaped ascospores within the family Saccharomycetaceae. After comparison of sequences from the complete genes of the 18S rDNA the genus Kluyveromyces appears heterogeneous. The type species of the genus, K. polysporus is congeneric with the genus Saccharomyces. The data of Cai et al. (1996; Int. J. Syst. Bacteriol. 46, 542-549) and our own data suggest to conserve the genus Kluyveromyces for a clade containing K. marxianius, K. dobzhanskii, K. wickerhamii and K. aestuarii, which again can be included in the family Saccharomycetaceae. The phylogenetic age of the Metschnikowiaceae and Saccharomycetaceae will be discussed in the light of coevolution.

Mutants in the Saccharomyces cerevisiae RAS2 gene influence life span, cytoskeleton, and regulation of mitosis

We investigated the phenotypic consequences in Saccharomyces cerevisiae of a disruption allele (ras2::LEU2) and of a dominant mutant form (RAS2ala18,val19) of RAS2. In addition to the phenotypes described earlier for these mutants, we observed a small increase in the life span for the disruption allele and a drastic decrease of life span for the dominant mutant form, as compared with the isogenic wild type. This was found by analyzing these alleles in two different genetic backgrounds with nearly the same results. Life spans were determined by micromanipulating mother cells and counting generations until no further cell division occurred. A morphological analysis of the terminal phenotypes of very old mother cells was performed showing enlarged or rounded cells and in some cases elongated buds, some of which were difficult to separate from the mother cell. This was observed in wild-type cells, as well as mutant cells. However, the dominant RAS2 mutant (but not the wild-type or ras2::LEU2 mutant cells) after 2 days on complex media displayed phenotypes similar to the terminal phenotype of old mothers. A substantial fraction of the cells were enlarged and generated elongated buds, they lost Calcofluor staining of the bud scars, the cell surface appeared folded, the actin cytoskeleton was aberrant, and the mitotic spindle and the cytoplasmic microtubles were defective in their proper orientation, resulting in aberrant mitoses and empty buds. These phenotypic characteristics of the RAS2ala18,val19 mutation could be causative for the previously observed rapid loss of viability of these cells in stationary phase.

Enolases are highly conserved fungal allergens

BACKGROUND

Lack of knowledge of the identity of fungal allergens still is a major obstacle for improvement of diagnosis and therapy of allergies to moulds. We have therefore further analyzed the allergens of the two moulds, Alternaria alternata and Cladosporium herbarum and found that enolases (EC 4.2.1.11) are major allergens, at least of the two fungal species just mentioned.

METHODS

The enolases of Alternaria and Cladosporium were cloned from cDNA libraries constructed from vegetative cells of the two moulds by immunological screening with sera from selected patients allergic to the moulds. The two enolases were expressed as recombinant nonfusion proteins and used for determination of the incidence of allergy to enolase among a cohort of patients.

RESULTS

Sequencing of the two enolases showed very close relationships with other known fungal enolase sequences. Competition experiments using immunoblots of the recombinant nonfusion proteins showed nearly complete identity of the epitopes on both enolases. Serum from a patient reactive to Cladosporium enolase reacted equally well with the enolases of Alternaria, Saccharomyces and Candida. About 50% each of the sera from patients reactive to Cladosporium and Alternaria were strongly reactive to the recombinant enolases.

CONCLUSIONS

Enolases are therefore considered to be highly conserved major fungal allergens.

Isoforms of atopic allergens with reduced allergenicity but conserved T cell antigenicity: possible use for specific immunotherapy

BACKGROUND

We analyzed the T cell activation potency and the IgE-binding properties (allergenicity) of nine isoforms of Bet v 1, the major allergen of birch pollen.

METHODS

The capacity of recombinant Bet v 1 isoforms to bind serum IgE from allergic patients was evaluated by immunoblot experiments and skin prick tests. The potency of Bet v 1 isoallergens to activate T lymphocytes from birch-pollen-allergic patients was assayed using allergen-specific T cell clones.

RESULTS

According to their ability to bind IgE from allergic patients in immunoblot experiments, Bet v 1 isoforms can be grouped into high-IgE-binding molecules and molecules with low/no IgE-binding activity. Representatively, isoform d was used in skin tests. Skin prick tests revealed no potency of this isoform to induce wheal and flare reactions in the skin of birch-pollen-allergic individuals. In contrast, isoform a and natural Bet v 1 displayed high allergenicity in vivo. On the other hand, Bet v 1 isoform d (low allergenicity) displayed significant higher T cell activation potency when compared to isoform a (high allergenicity).

CONCLUSION

Based on these findings, we propose a new form of specific immunotherapy using hypoallergenic recombinant allergen isoforms.

Secondary structure and tertiary fold of the birch pollen allergen Bet v 1 in solution

Bet v 1 is the major birch pollen allergen and therefore the main cause of type I allergies observed in early spring. It is composed of 159 amino acid residues adding up to a molecular mass of 17 kDa. We determined the secondary structure and tertiary fold of full-length Bet v 1 by NMR spectroscopy. Two- and three-dimensional NMR measurements suggest that Bet v 1 is a globular monomer in solution with a high content of well defined secondary structure. Of the total of 159 residues, 135 could be sequentially assigned, using an improved assignment strategy based mainly on heteronuclear experiments. An improved strategy for structure calculation revealed three helices and two beta-sheets as major elements of secondary structure. The globular tertiary structure is mainly stabilized by two antiparallel beta-sheets. The two helices at the C terminus are in accordance with the results from the solution structure of the chemically synthesized peptide Bet v 1-(125-154). This peptide is composed of two helices connected by a hinge. The structural features of Bet v 1 are highly similar to those found in the Ambrosia allergen Amb t V.

High-level expression of tree pollen isoallergens in Escherichia coli

cDNAs coding for the major allergen of alder (Alnus glutinosa) pollen Aln g 1, for nine isoforms of Bet v 1, the major birch (Betula verrucosa) pollen allergen, and for four isoforms of Cor a 1, the major allergen of hazel (Corylus avellana) pollen, were inserted into the plasmid pMW175 or pMW 172 and expressed in Escherichia coli as recombinant non-fusion proteins. These constructs produced between 20 and 160 mg protein/l. The recombinant tree pollen isoallergens were tested in immunoblots for their antibody binding properties. For this purpose, we used two monoclonal antibodies (BIP 1 and BIP 4) raised against natural Bet v 1, a polyclonal rabbit anti-recombinant Bet v 1a, as well as serum IgE from allergic patients. Our results show that this expression system is suitable for the production of milligram amounts of tree pollen isoallergens which can be used for the characterization of allergenic epitopes recognized by T and B cells.

N,N'-Bisformyl dityrosine is an in vivo precursor of the yeast ascospore wall

The amino acid, dityrosine, is a major component of the spore wall surface of the yeast Saccharomyces cerevisiae, where it is part of a highly cross-linked macromolecular network of yet unknown chemical structure, consisting mostly of glucosamine, dityrosine and few other amino acids. Biosynthesis of the dityrosine moiety of this network consists of several steps, including the chemical modification of free L-tyrosine and the subsequent oxidative cross-linking of the modified tyrosine residues (catalyzed by a cytochrome P-450), leading to soluble dityrosine-containing spore wall precursors. We isolated, purified and characterized the dityrosine-containing precursor that appears late in spore wall synthesis and that is thought to be directly incorporated into the maturing spore wall. Chemical and spectroscopic analyses showed that this precursor is N,N'-bisformyl dityrosine. In addition, we identified a tyrosine-containing spore wall precursor as N-formyl tyrosine. The elucidation of the chemical structure of soluble spore wall precursors is crucial for the characterization of the function of the enzymes involved in maturation of the spore surface, e.g. by in vitro systems. A dityrosine-containing fragment, which was solubilized from mature spore walls by partial hydrolysis, was identified as N-formyl dityrosine. Mature spore walls contain significant amounts of N-formyl dityrosine and N,N'-bisformyl dityrosine. This supports the assumption that the dityrosine-containing macromolecular network on the spore surface has an unusual, non-peptidic structure.

Evidence for an alpha helical T cell epitope in the C-terminus of the main birch pollen allergen Bet V 1

Secondary structure prediction of the main birch pollen allergen Bet v 1 was found to be in good agreement with the secondary structural elements found by analysing the Bet v 1 circular dichroism data. According to both experiment and prediction, 32% of 160 amino acids participate in alpha helices, 21% in beta sheets, 24% in turns, and 23% in other structural motifs. The peptide LRAVESYLLAHS which represents one of the major T cell epitopes on Bet v 1 was shown to have a high propensity to form an alpha helix. Time-resolved fluorescence anisotropy measurements of the allergen revealed an overall rotational correlation time of 7.35 ns, which corresponds to a hydrodynamic molecular radius of 19.2 A. This refers to a monomeric Bet v 1 molecule in solution, which is also reflected in the narrow band width of the 1H-NMR spectrum. The results presented here are in good agreement with the recently solved NMR structure of Amb t 5: both allergens are monomers in solution with an extended C-terminal alpha helix containing a major T cell epitope.

Dissection of immunoglobulin E and T lymphocyte reactivity of isoforms of the major birch pollen allergen Bet v 1: potential use of hypoallergenic isoforms for immunotherapy

We dissected the T cell activation potency and the immunoglobulin (Ig) E-binding properties (allergenicity) of nine isoforms of Bet v 1 (Bet v 1a-Bet v 1l), the major birch pollen allergen. Immunoblot experiments showed that Bet v 1 isoforms differ in their ability to bind IgE from birch pollen-allergic patients. All patients tested displayed similar IgE-binding patterns toward each particular isoform. Based on these experiments, we grouped Bet v 1 isoforms in three classes: molecules with high IgE-binding activity (isoforms a, e, and j), intermediate IgE-binding (isoforms b, c, and f), and low/no IgE-binding activity (isoforms d, g, and 1). Bet v 1a, a recombinant isoform selected from a cDNA expression library using IgE immunoscreening exhibited the highest IgE-binding activity. Isoforms a, b, d, e, and 1 were chosen as representatives from the three classes for experimentation. The potency of each isoallergen to activate T lymphocytes from birch pollen-allergic patients was assayed using peripheral blood mononuclear cells, allergen-specific T cell lines, and peptide-mapped allergen-specific T cell clones. Among the patients, some displayed a broad range of T cell-recognition patterns for Bet v 1 isoforms whereas others seemed to be restricted to particular isoforms. In spite of this variability, the highest scores for T cell proliferative responses were observed with isoform d (low IgE binder), followed by b, 1, e, and a. In vivo (skin prick) tests showed that the potency of isoforms d and 1 to induce typical urticarial type 1 reactions in Bet v 1-allergic individuals was significantly lower than for isoforms a, b, and e. Taken together, our results indicate that hypoallergenic Bet v 1 isoforms are potent activators of allergen-specific T lymphocytes, and Bet v 1 isoforms with high in vitro IgE-binding activity and in vivo allergenicity can display low T cell antigenicity. Based on these findings, we propose a novel approach for immunotherapy of type I allergies: a treatment with high doses of hypoallergenic isoforms or recombinant variants of atopic allergens. We proceed on the assumption that this measure would modulate the quality of the T helper cell response to allergens in vivo. The therapy form would additionally implicate a reduced risk of anaphylactic side effects.

Biological and immunological importance of Bet v 1 isoforms

In 2D-PAGE analysis of Bet v 1, the major birch pollen allergen, up to 12 isoforms can be demonstrated that differ in their isoelectric points from about pH 4.9 to pH 5.9. The molecular weights of these isoforms seem to be rather similar, but minor variations can also be seen. Preliminary experiments with birch leaves seem to indicate that in aging leaves some isoforms can be found that do not occur in pollen. In birch cells cultured in vitro, Bet v 1 isoforms can be induced by bacterial infection that do not occur in pollen (Swoboda et al. (1995), Pant, Cell and Environment 18, 865-874). In a recent paper (Swoboda et al (1995)., J. Biol. Chem. 270, 2607-2613) we show that in natural Bet v 1 from pollen the isoforms are due to different protein sequences. The derived protein sequences of 10 different isoforms (corresponding to 13 different cDNAs) were determined and confirmed by plasma desorption mass spectrometry of purified natural Bet v 1 after trypsin and endoproteinase Glu-C digestion. These experiments also showed that pollen Bet v 1 isoforms were reactive to patients' sera to different degrees and that common post-synthetic modifications (besides N-terminal methionine cleavage) did not occur on Bet v 1. Recombinant isoforms were produced in E. coli, purified and tested with selected patients allergic to birch pollen (Ferreira et al., J. Exp. Med., in the press). The pattern of IgE binding to Bet v 1 isoforms widely differs. Also, T-cell clones from individual patients in some cases are specific to peptides occurring only in certain isoforms. It was of particular interest that three of the naturally occurring pollen Bet v 1 isoforms do not or hardly bind IgE of untreated patients allergic to Bet v 1. However, a comparison of IgE reactivity in patients before and after conventional immunotherapy with natural pollen extract clearly showed that this form of immunotherapy induced IgE to the isoforms that had been unreactive in untreated patients. One of these, Bet v 1d, showed a particularly strong potency towards T-cell stimulation. The isoform(s) that do not bind IgE in untreated patients but still show T-cell reactivity could be potentially utilized for a new form of immunotherapy that avoids the risk of anaphylaxis.

The yeast growth control gene GRC5 is highly homologous to the mammalian putative tumor suppressor gene QM

We isolated the Saccharomyces cerevisiae GRC5 (growth control) gene by functional complementation in vivo of a ts (temperature sensitive) mutation. Phenotypic analysis suggested involvement of GRC5 in cell growth and proliferation. Mutant cells arrest their cell cycles after one to three cell divisions predominantly as mother cells with a large bud. In the region of the septum, a massive accumulation of cell wall material is observed. The mother and daughter nuclei are well separated and spindles are no longer present, while the cytoskeleton is of aberrant appearance. Arrested cells do not perform protein synthesis and are unable to mate. Furthermore, grc5-1ts cells rapidly lose viability at the restrictive temperature (37 degrees C) only on full media, but not under nitrogen-starvation conditions, indicating that proper response to this nutrient limitation is still intact in mutant cells after cell cycle arrest. The sequence of GRC5 translates into a basic protein of 221 amino acid with a corresponding Mr of 25.4 kDa. GRC5 is a member of the highly conserved QM gene family, members of which have been reported from plants, invertebrates and vertebrates. The amino acid sequence of GRC5 over its entire length is more than 60% identical to the human QM protein, expression of which is associated with loss of the tumorigenic phenotype in a cell line derived from Wilms' tumor, a malignancy of the embyronic kidney. Here, we show that GRC5 is an essential yeast gene, the function of which as inferred from analysis of the grc5-1ts mutant is crucial for establishment of proper cytoskeletal structure and regulation of growth in yeast cells.

Strain-dependent occurrence of functional GTP:AMP phosphotransferase (AK3) in Saccharomyces cerevisiae

The gene for yeast GTP:AMP phosphotransferase (PAK3) was found to encode a nonfunctional protein in 10 laboratory strains and one brewers' strain. The protein product showed high similarity to vertebrate AK3 and was located exclusively in the mitochondrial matrix. The deduced amino acid sequence revealed a protein that was shorter at the carboxyl terminus than all other known adenylate kinases. Introduction of a +1 frameshift into the 3'-terminal region of the gene extended homology of the deduced amino acid sequence to other members of the adenylate kinase family including vertebrate AK3. Frameshift mutations obtained after in vitro and in vivo mutagenesis were capable of complementing the adk1 temperature-conditional deficiency in Escherichia coli, indicating that the frameshift led to the expression of a protein that could phosphorylate AMP. Some yeasts, however, including strain D273-10B, two wine yeasts, and two more distantly related yeast genera, harbored an active allele, named AKY3, which contained a +1 frameshift close to the carboxyl terminus as compared with the laboratory strains. The encoded protein exhibited GTP:AMP and ITP:AMP phosphotransferase activities but did not accept ATP as phosphate donor. Although single copy in the haploid genome, disruption of the AKY3 allele displayed no phenotype, excluding the possibility that laboratory and brewers' strains had collected second site suppressors. It must be concluded that yeast mitochondria can completely dispense with GTP:AMP phosphotransferase activity.

Molecular cloning of major and minor allergens of Alternaria alternata and Cladosporium herbarum

The two moulds, Alternaria alternata and Cladosporium herbarum, are recognized as major causes of fungal allergies. Cloning, sequencing and heterologous expression of the allergens of the two moulds is a necessary step in understanding fungal allergy and in the development of new and improved methods of diagnosis and therapy. The seven new mould allergens presented here represent four new allergen proteins: aldehyde dehydrogenase (ALDH), enolase, YCP4 (previously found as a Saccharomyces cerevisiae protein of unknown function), and the acidic ribosomal protein, P2. Three of them (ALDH, YCP4 and P2) were found to be allergens in both fungi, Alternaria and Cladosporium. All allergens found so far are cytoplasmic proteins and are rather well conserved in evolution even when comparing distant species. Most of the allergens have "household" functions (ALDH, enolase). One allergen (P2) is a homolog of a very highly conserved human lupus erythematodes (LE) antigen. None of the fungal allergens is clearly related to other known non-fungal allergens.

Molecular dynamics simulation of the rare amino acid LL-dityrosine and a dityrosine-containing peptide: comparison with time-resolved fluorescence

The fluorescence of the rare amino acid LL-dityrosine, which is found in insoluble biological materials with structural features, was recently shown to decay non-exponentially (Kungl et al. (1992) J. Fluorescence 2, 63-74). Here we investigated the time-resolved fluorescence of a dityrosine-containing peptide (DCP) to study the influence of side chains on the fluorescence decay of the chromophore. The fluorescence decay of DCP was best fitted by three exponential terms including a sub-nanosecond rise term, the values of which are quite similar to the parameters obtained for the decay of free dityrosine. They were found to depend on the pH of the aqueous solution but not on the temperature. Analysis by an exponential series method revealed broad fluorescence lifetime distributions for DCP. Compared to the corresponding analysis of dityrosine transients, similar lifetime centers were found whereas the widths of the distributions were found broader for DCP. Molecular dyamics (MD) simulations of dityrosine at 300 K show that chi 1 and chi 2 side chain conformers (rotamers) of both tyrosine subunits interconvert on a picosecond timescale. The rates of interconversion were shown to depend critically upon the MD technique applied: in vacuo simulations yielded lower interconversion rates compared to stochastic dynamics (SD) and full MD (water explicitly included). However, MD simulations of the dityrosine-containing peptide revealed no interconversions of the chi 1 and chi 2 side chain rotamers of both tyrosine subunits within a 400 ps trajectory. Interconversions could be induced by raising the temperature of the system (DCP plus solvent) to 340 K. Side chain rotamers of dityrosine are not stable on a fluorescence time scale but are stable when a dityrosine-containing peptide is regarded. Nevertheless both molecules yield similar fluorescence decay patterns. We therefore conclude that the rotamer model proposed for the fluorescence decay of tyrosine and tryptophan cannot be applied to the fluorescence decay of dityrosine and peptides containing this chromophore. This should be of future interest when dityrosine is used as an intrinsic sensor to study complex dityrosine-containing macromolecules by fluorescence spectroscopy.

A birch gene family encoding pollen allergens and pathogenesis-related proteins

Bet v I, the major pollen allergen of birch (Betula verrucosa), shows high sequence homology to a family of pathogenesis-related (PR) proteins that have recently been identified in several other plant species. We have used a pollen Bet v I cDNA clone and anti-Bet v I antibodies as probes to study the expression of Bet v I genes in birch cell suspension cultures under different experimental conditions. Induction of Bet v I-related proteins was detected in immunoblots of cell extracts upon co-cultivation with microbial pathogens. Northern analysis revealed the rapid induction of Bet v I transcripts in the presence of bacteria and fungi, but not by stress treatments (heat shock, metal ions) or by chemical elicitors. RNase protection experiments showed that the pathogen-inducible RNAs did not correspond to the pollen cDNA clone but most likely to the products of transcription of other members of the Bet v I gene family, sharing high sequence homology with the pollen-specific gene within the 5'-half of the coding region. We conclude that the Bet v I gene family of pollen allergens includes a subset of defense-related genes that are transcriptionally activated in the presence of microbial pathogens.

Time-resolved fluorescence studies of dityrosine in the outer layer of intact yeast ascospores

The (time-resolved) fluorescence properties of dityrosine in the outermost layer of the spore wall of Saccharomyces cerevisiae were investigated. Steady-state spectra revealed an emission maximum at 404 nm and a corresponding excitation maximum at 326 nm. The relative fluorescence quantum yield decreased with increasing proton concentration. The fluorescence decay of yeast spores was found to be nonexponential and differed pronouncedly from that of unbound dityrosine in water. Analysis of the spore decay recorded at lambda ex = 323 nm and lambda em = 404 nm by an exponential series (ESM) algorithm revealed a bimodal lifetime distribution with maxima centered at tau 1C = 0.5 ns and tau 2C = 2.6 ns. The relative amplitudes of the two distributions are shown to depend on the emission wavelength, indicating contributions from spectrally different dityrosine chromophores. On quenching the spore fluorescence with acrylamide, a downward curvature of the Stern-Volmer plot was obtained. A multitude of chromophores more or less shielded from solvent in the spore wall is proposed to account for the nonlinear quenching of the total spore fluorescence. Analysis of the fluorescence anisotropy decay revealed two rotational correlation times (phi 1 = 0.9 ns and phi 2 = 30.6 ns) or a bimodal distribution of rotational correlation times (centers at 0.7 ns and 40 ns) when the data were analyzed by the maximum entropy method (MEM). We present a model that accounts for the differences between unbound (aqueous) and bound (incorporated in the spore wall) dityrosine fluorescence. The main feature of the photophysical model for yeast spores is the presence of at least two species of dityrosine chromophores differing in their chemical environments. A hypothetical photobiological role of these fluorophores in the spore wall is discussed: the protection of the spore genome from mutagenic UV light.