Five Genes Involved in Biosynthesis of the Pyruvylated Galβ1,3-Epitope in Schizosaccharomyces pombe N-Linked Glycans

Identification of a putative α-galactoside β-(1 → 3)-galactosyltransferase involved in the biosynthesis of galactomannan side chain of glucuronoxylomannogalactan in Cryptococcus neoformans

The cell surface of Cryptococcus neoformans is covered by a thick capsular polysaccharide. The capsule is the most important virulence factor of C. neoformans; however, the complete mechanism of its biosynthesis is unknown. The capsule is composed of glucuronoxylomannan (GXM) and glucuronoxylomannogalactan (GXMGal). As GXM is the most abundant component of the capsule, many studies have focused on GXM biosynthesis. However, although GXMGal has an important role in virulence, studies on its biosynthesis are scarce. Herein, we have identified a GT31 family β-(1 → 3)-galactosyltransferase Ggt2, which is involved in the biosynthesis of the galactomannan side chain of GXMGal. Comparative analysis of GXMGal produced by a ggt2 disruption strain revealed that Ggt2 is a glycosyltransferase that catalyzes the initial reaction in the synthesis of the galactomannan side chain of GXMGal. The ggt2 disruption strain showed a temperature-sensitive phenotype at 37°C, indicating that the galactomannan side chain of GXMGal is important for high-temperature stress tolerance in C. neoformans. Our findings provide insights into complex capsule biosynthesis in C. neoformans.

The antioxidant activity of polysaccharides: A structure-function relationship overview

Over the last years, polysaccharides have been linked to antioxidant effects using both in vitro chemical and biological models. The reported structures, claimed to act as antioxidants, comprise chitosan, pectic polysaccharides, glucans, mannoproteins, alginates, fucoidans, and many others of all type of biological sources. The structural features linked to the antioxidant action include the polysaccharide charge, molecular weight, and the occurrence of non-carbohydrate substituents. The establishment of structure/function relationships can be, however, biased by secondary phenomena that tailor polysaccharides behavior in antioxidant systems. In this sense, this review confronts some basic concepts of polysaccharides chemistry with the current claim of carbohydrates as antioxidants. It critically discusses how the fine structure and properties of polysaccharides can define polysaccharides as antioxidants. Polysaccharides antioxidant action is highly dependent on their solubility, sugar ring structure, molecular weight, occurrence of positive or negatively charged groups, protein moieties and covalently linked phenolic compounds. However, the occurrence of phenolic compounds and protein as contaminants leads to misleading results in methodologies often used for screening and characterization purposes, as well as in vivo models. Despite falling in the concept of antioxidants, the role of polysaccharides must be well defined according with the matrices where they are involved.

In vivo imaging of fluorescent albumin modified with pyruvylated-human-type complex oligosaccharide reveals sialylation-like biodistribution and kinetics

Both pyruvylation and sialylation onto the terminus of oligosaccharides of N-glycoproteins seem to be structurally and functionally similar with a property of conferring negative charge. However, detailed molecular characteristics of pyruvylation and sialylation in vivo were elusive. Here, to investigate an effect of terminal pyruvylation to N-glycan on in vivo biodistribution and kinetics, we prepared human serum albumin (HSA) modified with pyruvylated N-glycan (PvG), conjugated with HiLyte Fluor 750 (FL750-PvGHSA). In vivo imaging by using FL750-PvGHSA revealed that terminally pyruvylated N-glycoalbumin was excreted like sialylated N-glycoalbumin, suggesting that pyruvylation mimics sialylation in in vivo biodistribution and kinetics of N-glycoproteins. Terminal pyruvylation onto N-glycans can be a potential tool for a novel glycoengineering strategy.

Substrate specificities of α1,2- and α1,3-galactosyltransferases and characterization of Gmh1p and Otg1p in Schizosaccharomyces pombe

In the fission yeast Schizosaccharomyces pombe, α1,2- and α1,3-linked D-galactose (Gal) residues are transferred to N- and O-linked oligosaccharides of glycoproteins by galactosyltransferases. Although the galactomannans are important for cell-cell communication in S. pombe (e.g., in non-sexual aggregation), the mechanisms underlying galactosylation in cells remain unclear. S. pombe has 10 galactosyltransferase-related genes: seven belonging to glycosyltransferase (GT) family 34 and three belonging GT family 8. Disruption of all 10 α-galactosyltransferases (strain Δ10GalT) has been shown to result in a complete lack of α-Gal residues. Here, we have investigated the function and substrate specificities of galactosyltransferases in S pombe by using strains expressing single α-galactosyltransferases in the Δ10GalT background. High-performance liquid chromatography (HPLC) analysis of pyridylaminated O-linked oligosaccharides showed that two GT family 34 α1,2-galactosyltransferases (Gma12p and Gmh6p) and two GT family 8 α1,3-galactosyltransferases (Otg2p and Otg3p) are involved in galactosylation of O-linked oligosaccharide. Moreover, 1H-NMR of N-glycans revealed that three GT family 34 α1,2-galactosyltransferases (Gmh1p, Gmh2p, and Gmh3p) are required for galactosylation of N-linked oligosaccharides. Furthermore, HPLC and lectin-blot analysis revealed that Otg1p showed α1,3-galactosyltransferase activity under conditions of co-expression with Gmh6p, indicating that α-1,2-linked galactose is required for the galactosylation activity of Otg1p in S. pombe. In conclusion, eight galactosyltransferases have been shown to have activity in S. pombe with different substrate specificities. These findings will be useful for genetically tailoring the galactosylation of both N- and O- glycans in fission yeast.

Pyruvate Substitutions on Glycoconjugates

Glycoconjugates are the most diverse biomolecules of life. Mostly located at the cell surface, they translate into cell-specific "barcodes" and offer a vast repertoire of functions, including support of cellular physiology, lifestyle, and pathogenicity. Functions can be fine-tuned by non-carbohydrate modifications on the constituting monosaccharides. Among these modifications is pyruvylation, which is present either in enol or ketal form. The most commonly best-understood example of pyruvylation is enol-pyruvylation of N-acetylglucosamine, which occurs at an early stage in the biosynthesis of the bacterial cell wall component peptidoglycan. Ketal-pyruvylation, in contrast, is present in diverse classes of glycoconjugates, from bacteria to algae to yeast-but not in humans. Mild purification strategies preventing the loss of the acid-labile ketal-pyruvyl group have led to a collection of elucidated pyruvylated glycan structures. However, knowledge of involved pyruvyltransferases creating a ring structure on various monosaccharides is scarce, mainly due to the lack of knowledge of fingerprint motifs of these enzymes and the unavailability of genome sequences of the organisms undergoing pyruvylation. This review compiles the current information on the widespread but under-investigated ketal-pyruvylation of monosaccharides, starting with different classes of pyruvylated glycoconjugates and associated functions, leading to pyruvyltransferases, their specificity and sequence space, and insight into pyruvate analytics.

Anionic and zwitterionic moieties as widespread glycan modifications in non-vertebrates

Glycan structures in non-vertebrates are highly variable; it can be assumed that this is a product of evolution and speciation, not that it is just a random event. However, in animals and protists, there is a relatively limited repertoire of around ten monosaccharide building blocks, most of which are neutral in terms of charge. While two monosaccharide types in eukaryotes (hexuronic and sialic acids) are anionic, there are a number of organic or inorganic modifications of glycans such as sulphate, pyruvate, phosphate, phosphorylcholine, phosphoethanolamine and aminoethylphosphonate that also confer a 'charged' nature (either anionic or zwitterionic) to glycoconjugate structures. These alter the physicochemical properties of the glycans to which they are attached, change their ionisation when analysing them by mass spectrometry and result in different interactions with protein receptors. Here, we focus on N-glycans carrying anionic and zwitterionic modifications in protists and invertebrates, but make some reference to O-glycans, glycolipids and glycosaminoglycans which also contain such moieties. The conclusion is that 'charged' glycoconjugates are a widespread, but easily overlooked, feature of 'lower' organisms.

Identification and characterization of a novel β-D-galactosidase that releases pyruvylated galactose

Pyruvyl modification of oligosaccharides is widely seen in both prokaryotes and eukaryotes. Although the biosynthetic mechanisms of pyruvylation have been investigated, enzymes that metabolize and degrade pyruvylated oligosaccharides are not well known. Here, we searched for a pyruvylated galactose (PvGal)-releasing enzyme by screening soil samples. We identified a Bacillus strain, as confirmed by the 16S ribosomal RNA gene analysis, that exhibited PvGal-ase activity toward p-nitrophenyl-β-D-pyruvylated galactopyranose (pNP-β-D-PvGal). Draft genome sequencing of this strain, named HMA207, identified three candidate genes encoding potential PvGal-ases, among which only the recombinant protein encoded by ORF1119 exhibited PvGal-ase activity. Although ORF1119 protein displayed broad substrate specificity for pNP sugars, pNP-β-D-PvGal was the most favorable substrate. The optimum pH for the ORF1119 PvGal-ase was determined as 7.5. A BLAST search suggested that ORF1119 homologs exist widely in bacteria. Among two homologs tested, BglC from Clostridium but not BglH from Bacillus showed PvGal-ase activity. Crystal structural analysis together with point mutation analysis revealed crucial amino acids for PvGal-ase activity. Moreover, ORF1119 protein catalyzed the hydrolysis of PvGal from galactomannan of Schizosaccharomyces pombe, suggesting that natural polysaccharides might be substrates of the PvGal-ase. This novel PvGal-catalyzing enzyme might be useful for glycoengineering projects to produce new oligosaccharide structures.

Glycan Alteration Imparts Cellular Resistance to a Membrane-Lytic Anticancer Peptide

Although resistance toward small-molecule chemotherapeutics has been well studied, the potential of tumor cells to avoid destruction by membrane-lytic compounds remains unexplored. Anticancer peptides (ACPs) are a class of such agents that disrupt tumor cell membranes through rapid and non-stereospecific mechanisms, encouraging the perception that cellular resistance toward ACPs is unlikely to occur. We demonstrate that eukaryotic cells can, indeed, develop resistance to the model oncolytic peptide SVS-1, which preferentially disrupts the membranes of cancer cells. Utilizing fission yeast as a model organism, we show that ACP resistance is largely controlled through the loss of cell-surface anionic saccharides. A similar mechanism was discovered in mammalian cancer cells where removal of negatively charged sialic acid residues directly transformed SVS-1-sensitive cell lines into resistant phenotypes. These results demonstrate that changes in cell-surface glycosylation play a major role in tumor cell resistance toward oncolytic peptides.

A rationally engineered yeast pyruvyltransferase Pvg1p introduces sialylation-like properties in neo-human-type complex oligosaccharide

Pyruvylation onto the terminus of oligosaccharide, widely seen from prokaryote to eukaryote, confers negative charges on the cell surface and seems to be functionally similar to sialylation, which is found at the end of human-type complex oligosaccharide. However, detailed molecular mechanisms underlying pyruvylation have not been clarified well. Here, we first determined the crystal structure of fission yeast pyruvyltransferase Pvg1p at a resolution of 2.46 Å. Subsequently, by combining molecular modeling with mutational analysis of active site residues, we obtained a Pvg1p mutant (Pvg1p(H168C)) that efficiently transferred pyruvyl moiety onto a human-type complex glycopeptide. The resultant pyruvylated human-type complex glycopeptide recognized similar lectins on lectin arrays as the α2,6-sialyl glycopeptides. This newly-generated pyruvylation of human-type complex oligosaccharides would provide a novel method for glyco-bioengineering.

Conserved and Diverged Functions of the Calcineurin-Activated Prz1 Transcription Factor in Fission Yeast

Gene regulation in response to intracellular calcium is mediated by the calcineurin-activated transcription factor Prz1 in the fission yeast Schizosaccharomyces pombe Genome-wide studies of the Crz1 and CrzA fungal orthologs have uncovered numerous target genes involved in conserved and species-specific cellular processes. In contrast, very few target genes of Prz1 have been published. This article identifies an extensive list of genes using transcriptome and ChIP-chip analyses under inducing conditions of Prz1, including CaCl2 and tunicamycin treatment, as well as a ∆pmr1 genetic background. We identified 165 upregulated putative target genes of Prz1 in which the majority contained a calcium-dependent response element in their promoters, similar to that of the Saccharomyces cerevisiae ortholog Crz1 These genes were functionally enriched for Crz1-conserved processes such as cell-wall biosynthesis. Overexpression of prz1(+)increased resistance to the cell-wall degradation enzyme zymolyase, likely from upregulation of theO-mannosyltransferase encoding gene omh1(+) Loss of omh1(+)abrogates this phenotype. We uncovered a novel inhibitory role in flocculation for Prz1. Loss of prz1(+)resulted in constitutive flocculation and upregulation of genes encoding the flocculins Gsf2 and Pfl3, as well as the transcription factor Cbf12. The constitutive flocculation of the ∆prz1 strain was abrogated by the loss of gsf2(+) or cbf12(+) This study reveals that Prz1 functions as a positive and negative transcriptional regulator of genes involved in cell-wall biosynthesis and flocculation, respectively. Moreover, comparison of target genes between Crz1/CrzA and Prz1 indicate some conservation in DNA-binding specificity, but also substantial rewiring of the calcineurin-mediated transcriptional regulatory network.

More Than Just Oligomannose: An N-glycomic Comparison of Penicillium Species

N-glycosylation is an essential set of post-translational modifications of proteins; in the case of filamentous fungi, N-glycans are present on a range of secreted and cell wall proteins. In this study, we have compared the glycans released by peptide/N-glycosidase F from proteolysed cell pellets of three Penicillium species (P. dierckxii, P. nordicum and P. verrucosum that all belong to the Eurotiomycetes). Although the major structures are all within the range Hex(5-11)HexNAc(2) as shown by mass spectrometry, variations in reversed-phase chromatograms and MS/MS fragmentation patterns are indicative of differences in the actual structure. Hydrofluoric acid and mannosidase treatments revealed that the oligomannosidic glycans were not only in part modified with phosphoethanolamine residues and outer chain och1-dependent mannosylation, but that bisecting galactofuranose was present in a species-dependent manner. These data are the first to specifically show the modification of N-glycans in fungi with zwitterionic moieties. Furthermore, our results indicate that mere mass spectrometric screening is insufficient to reveal the subtly complex nature of N-glycosylation even within a single fungal genus.

The fission yeast Pvg1p has galactose-specific pyruvyltransferase activity

N-Glycan from the fission yeast Schizosaccharomyces pombe contains outer-chain pyruvic acid 4,6-ketal-linked galactose (PvGal). Here, we characterized a putative S. pombe pyruvyltransferase, Pvg1p, reported to be essential for biosynthesis of PvGal. When p-nitrophenyl-β-Gal (pNP-β-Gal) was used as a substrate, the structure of the recombinant Pvg1p product was determined to be pNP-PvGal by one- and two-dimensional NMR spectroscopy. The recombinant Pvg1p transferred pyruvyl residues from phosphoenolpyruvate specifically to β-linked galactose.

Deciphering the transcriptional-regulatory network of flocculation in Schizosaccharomyces pombe

In the fission yeast Schizosaccharomyces pombe, the transcriptional-regulatory network that governs flocculation remains poorly understood. Here, we systematically screened an array of transcription factor deletion and overexpression strains for flocculation and performed microarray expression profiling and ChIP-chip analysis to identify the flocculin target genes. We identified five transcription factors that displayed novel roles in the activation or inhibition of flocculation (Rfl1, Adn2, Adn3, Sre2, and Yox1), in addition to the previously-known Mbx2, Cbf11, and Cbf12 regulators. Overexpression of mbx2(+) and deletion of rfl1(+) resulted in strong flocculation and transcriptional upregulation of gsf2(+)/pfl1(+) and several other putative flocculin genes (pfl2(+)-pfl9(+)). Overexpression of the pfl(+) genes singly was sufficient to trigger flocculation, and enhanced flocculation was observed in several combinations of double pfl(+) overexpression. Among the pfl1(+) genes, only loss of gsf2(+) abrogated the flocculent phenotype of all the transcription factor mutants and prevented flocculation when cells were grown in inducing medium containing glycerol and ethanol as the carbon source, thereby indicating that Gsf2 is the dominant flocculin. In contrast, the mild flocculation of adn2(+) or adn3(+) overexpression was likely mediated by the transcriptional activation of cell wall-remodeling genes including gas2(+), psu1(+), and SPAC4H3.03c. We also discovered that Mbx2 and Cbf12 displayed transcriptional autoregulation, and Rfl1 repressed gsf2(+) expression in an inhibitory feed-forward loop involving mbx2(+). These results reveal that flocculation in S. pombe is regulated by a complex network of multiple transcription factors and target genes encoding flocculins and cell wall-remodeling enzymes. Moreover, comparisons between the flocculation transcriptional-regulatory networks of Saccharomyces cerevisiae and S. pombe indicate substantial rewiring of transcription factors and cis-regulatory sequences.

Identification of novel α1,3-galactosyltransferase and elimination of α-galactose-containing glycans by disruption of multiple α-galactosyltransferase genes in Schizosaccharomyces pombe

The oligosaccharides from fission yeast Schizosaccharomyces pombe contain large amounts of D-galactose (Gal) in addition to D-mannose (Man), in contrast to the budding yeast Saccharomyces cerevisiae. Detailed structural analysis has revealed that the Gal residues are attached to the N- and O-linked oligosaccharides via α1,2- or α1,3-linkages. Previously we constructed and characterized a septuple α-galactosyltransferase disruptant (7GalTΔ) anticipating a complete lack of α-Gal residues. However, the 7GalTΔ strain still contained oligosaccharides consisting of α1,3-linked Gal residues, indicating the presence of at least one more additional unidentified α1,3-galactosyltransferase. In this study we searched for unidentified putative glycosyltransferases in the S. pombe genome sequence and identified three novel genes, named otg1(+)-otg3(+) (α one, three-galactosyltransferase), that belong to glycosyltransferase gene family 8 in the Carbohydrate Active EnZymes (CAZY) database. Gal-recognizing lectin blotting and HPLC analyses of pyridylaminated oligosaccharides after deletion of these three additional genes from 7GalTΔ strain demonstrated that the resultant disruptant missing 10 α-galactosyltransferase genes, 10GalTΔ, exhibited a complete loss of galactosylation. In an in vitro galactosylation assay, the otg2(+) gene product had Gal transfer activity toward a pyridylaminated Man(9)GlcNAc(2) oligosaccharide and pyridylaminated Manα1,2-Manα1,2-Man oligosaccharide. In addition, the otg3(+) gene product exhibited Gal transfer activity toward the pyridylaminated Man(9)GlcNAc(2) oligosaccharide. Generation of an α1,3-linkage was confirmed by HPLC analysis, α-galactosidase digestion analysis, (1)H NMR spectroscopy, and LC-MS/MS analysis. These results indicate that Otg2p and Otg3p are involved in α1,3-galactosylation of S. pombe oligosaccharides.

MADS box transcription factor Mbx2/Pvg4 regulates invasive growth and flocculation by inducing gsf2+ expression in fission yeast

The fission yeast Schizosaccharomyces pombe exhibits invasive growth and nonsexual flocculation in response to nitrogen limitation. Gsf2, a flocculin of fission yeast, is required not only for nonsexual flocculation but also for invasive growth through the recognition of galactose residues on cell surface glycoconjugates. We found that pyruvylation negatively regulates nonsexual flocculation by capping the galactose residues of N-linked galactomannan. We investigated whether pyruvylation also regulates invasive growth. The pvg4(+) gene originally was isolated as a multicopy suppressor of a pvg4 mutant defective in the pyruvylation of N-linked oligosaccharides. However, we did not detect a defect in cell surface pyruvylation in the pvg4/mbx2 deletion mutant, as assessed by alcian blue staining and a Q-Sepharose binding assay. Instead, the deletion prevented invasive growth under conditions of low nitrogen and high glucose, and it reduced the adhesion and flocculation of otherwise flocculent mutants by reducing gsf2(+) expression. mbx2(+)-overexpressing strains exhibited nonsexual and calcium-dependent aggregation, which was inhibited in the presence of galactose but mediated by the induction of gsf2(+). These findings indicate that Mbx2 mediates invasive growth and flocculation via the transcriptional activation of gsf2(+) in fission yeast. In addition, we found that fission yeast Mbx2 induces the nonsexual flocculation of budding yeast by the activation of FLO1.

Mutation in the pssM gene encoding ketal pyruvate transferase leads to disruption of Rhizobium leguminosarum bv. viciae-Pisum sativum symbiosis

AIMS

To study the question whether acidic exopolysaccharide (EPS) modification, e.g. pyruvylation, plays any role in the development of Rhizobium leguminosarum/Pisum sativum symbiosis.

METHOD AND RESULTS

The amino acid sequence deduced from the pssM gene, localized within the pss (polysaccharide synthesis) gene locus, was shown to be homologous to several known and putative ketal pyruvate transferases, including ExoV from Sinorhizobium meliloti and GumL from Xanthomonas campestris. Rh. l. bv. viciae strain VF39 carrying a Km-cassette insertion into the pssM gene was obtained by the gene replacement technique. Knock-out of pssM led to the absence of the pyruvic acid ketal group at the subterminal glucose in the repeating unit of EPS as it was shown by (13)C and (1)H nuclear magnetic resonance (NMR) analysis. Complementation in trans restored the EPS modification in the pssM mutant. Disruption of the pssM gene resulted also in the formation of aberrant non-nitrogen-fixing nodules on peas. Ultrastructural studies of mutant nodules revealed normal nodule invasion and release of bacteria into the plant cell cytoplasm, but further differentiation of bacteroids was impaired, and the existing symbiosomes underwent lysis.

CONCLUSION

PssM encodes ketal pyruvate transferase involved in the modification of the Rh. l. bv. viciae EPS. The absence of subterminal glucose pyruvylation in the EPS repeating units negatively influences (directly or indirectly) the formation of the nitrogen-fixing symbiosis with peas.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our finding that the absence of modification even at the single position of EPS is likely to be crucial for establishment of nitrogen-fixing symbiosis argues in favour of the idea concerning their specific signalling role in this process.

Characterization of two different types of UDP-glucose/-galactose 4-epimerase involved in galactosylation in fission yeast

Schizosaccharomyces species are currently the only known organisms with two types of genes encoding UDP-glucose/-galactose 4-epimerase, uge1(+) and gal10(+). A strain deleted for uge1(+) exhibited a severe galactosylation defect and a decrease in activity and in UDP-galactose content when grown in glucose-rich medium (2 % glucose), indicating that Uge1p is a major UDP-glucose/-galactose 4-epimerase under these growth conditions. In contrast, gal10(+) was efficiently expressed and involved in galactosylation of cell-surface proteins in low-glucose medium (0.1 % glucose and 2 % glycerol), but not in galactose-containing medium. In a uge1Deltagal10Delta strain, the galactosylation defect was suppressed and UDP-galactose content restored to wild-type levels in galactose-containing medium. Disruption of gal7(+), encoding galactose-1-phosphate uridylyltransferase, in the uge1Deltagal10Delta strain reversed suppression of the galactosylation defect and reduced levels of UDP-galactose, indicating that galactose is transported from the medium to the cytosol and is converted into UDP-galactose via galactose 1-phosphate by Gal7p in Sch. pombe.

Production of heterologous proteins using the fission-yeast (Schizosaccharomyces pombe) expression system

The fission yeast Schizosaccharomyces pombe is a particularly useful model for studying the function and regulation of genes from higher eukaryotes. The genome of Sc. pombe has been sequenced, and DNA microarray, proteome and transcriptome analyses have been carried out. Among the well-characterized yeast species, Sc. pombe is considered an attractive host for the production of heterologous proteins. Expression vectors for high-level expression in Sc. pombe have been developed and many foreign proteins have been successfully expressed. However, further improvements in the protein-expressing host systems are still required for the production of heterologous proteins involved in post-translational modification, metabolism and intracellular trafficking. This minireview focuses on recent advances in heterologous protein production by use of engineered fission-yeast strains.

Adhesion molecules and other secreted host-interaction determinants in Apicomplexa: insights from comparative genomics

Apicomplexa have developed distinctive adaptations for invading and surviving within animal cells. Here a synthetic overview of the diversity and evolutionary history of cell membrane-associated, -secreted, and -exported proteins related to apicomplexan parasitism is presented. A notable feature in this regard was the early acquisition of adhesion protein domains and glycosylation systems through lateral transfer from animals. These were utilized in multiple contexts, including invasion of host cells and parasite-specific developmental processes. Apicomplexans possess a specialized version of the ancestral alveolate extrusion machinery, the rhoptries and micronemes, which are deployed in invasion and delivery of proteins into host cells. Each apicomplexan lineage has evolved a unique spectrum of extruded proteins that modify host molecules in diverse ways. Hematozoans, in particular, appear to have evolved novel systems for export of proteins into the host organelles and cell membrane during intracellular development. These exported proteins are an important aspect of the pathogenesis of Plasmodium and Theileria, being involved in response to fever and in leukocyte proliferation respectively. The complement of apicomplexan surface proteins has primarily diversified via massive lineage-specific expansions of certain protein families, which are often coded by subtelomeric gene arrays. Many of these families have been found to be central to immune evasion. Domain shuffling and accretion have resulted in adhesins with new domain architectures. In terms of individual genes, constant selective pressures from the host immune response has resulted in extensive protein polymorphisms and gene losses. Apicomplexans have also evolved complex regulatory mechanisms controlling expression and maturation of surface proteins at the chromatin, transcriptional, posttranscriptional, and posttranslational levels. Evolutionary reconstruction suggests that the ancestral apicomplexan had thrombospondin and EGF domain adhesins, which were linked to the parasite cytoskeleton, and played a central role in invasion through formation of the moving junction. It also suggests that the ancestral parasite had O-linked glycosylation of surface proteins which was partially or entirely lost in hematozoan lineages.

Fkh2p and Sep1p regulate mitotic gene transcription in fission yeast

In the fission yeast Schizosaccharomyces pombe, several genes including cdc15+, spo12+, fin1+, slp1+, ace2+ and plo1+ are periodically expressed during M phase. The products of these genes control various aspects of cell cycle progression including sister chromatid separation, septation and cytokinesis. We demonstrate that periodic expression of these genes is regulated by a common promoter sequence element, named a PCB. In a genetic screen for cell cycle regulators we have identified a novel forkhead transcription factor, Fkh2p, which is periodically phosphorylated in M phase. We show that Fhk2p and another forkhead transcription factor, Sep1p, are necessary for PCB-driven M-phase-specific transcription. In a previous report we identified a complex by electrophoretic mobility shift assay, which we termed PBF, that binds to a 150 bp region of the cdc15+ promoter that contains the PCB element. We have identified Mbx1p, a novel MADS box protein, as a component of PBF. However, although Mbx1p is periodically phosphorylated in M phase, Mbx1p is not required for periodic gene transcription in M phase. Moreover, although PBF is absent in strains bearing a C-terminal epitope tag on Fkh2p, simultaneous deletion of fkh2+ and sep1+ does not abolish PBF binding activity. This suggests that Mbx1p binds to gene promoters, but is not required for transcriptional activation. Together these results suggest that the activation of the Fkh2p and Sep1p forkhead transcription factors triggers mitotic gene transcription in fission yeast.

Current awareness on yeast

In order to keep subscribers up‐to‐date with the latest developments in their field, this current awareness service is provided by John Wiley & Sons and contains newly‐published material on yeasts. Each bibliography is divided into 10 sections. 1 Books, Reviews & Symposia; 2 General; 3 Biochemistry; 4 Biotechnology; 5 Cell Biology; 6 Gene Expression; 7 Genetics; 8 Physiology; 9 Medical Mycology; 10 Recombinant DNA Technology. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted. (4 weeks journals ‐ search completed 10th. Nov. 2004)