Modulation of the chromatin phosphoproteome by the Haspin protein kinase.

Recent discoveries have highlighted the importance of Haspin kinase activity for the correct positioning of the kinase Aurora B at the centromere. Haspin phosphorylates Thr(3) of the histone H3 (H3), which provides a signal for Aurora B to localize to the centromere of mitotic chromosomes. To date, histone H3 is the only confirmed Haspin substrate. We used a combination of biochemical, pharmacological, and mass spectrometric approaches to study the consequences of Haspin inhibition in mitotic cells. We quantified 3964 phosphorylation sites on chromatin-associated proteins and identified a Haspin protein-protein interaction network. We determined the Haspin consensus motif and the co-crystal structure of the kinase with the histone H3 tail. The structure revealed a unique bent substrate binding mode positioning the histone H3 residues Arg(2) and Lys(4) adjacent to the Haspin phosphorylated threonine into acidic binding pockets. This unique conformation of the kinase-substrate complex explains the reported modulation of Haspin activity by methylation of Lys(4) of the histone H3. In addition, the identification of the structural basis of substrate recognition and the amino acid sequence preferences of Haspin aided the identification of novel candidate Haspin substrates. In particular, we validated the phosphorylation of Ser(137) of the histone variant macroH2A as a target of Haspin kinase activity. MacroH2A Ser(137) resides in a basic stretch of about 40 amino acids that is required to stabilize extranucleosomal DNA, suggesting that phosphorylation of Ser(137) might regulate the interactions of macroH2A and DNA. Overall, our data suggest that Haspin activity affects the phosphorylation state of proteins involved in gene expression regulation and splicing.

How COVID-19 changed clinical research strategies: a global survey.

OBJECTIVE: Clinical research has faced new challenges during the COVID-19 pandemic, leading to excessive operational demands affecting all stakeholders. We evaluated the impact of COVID-19 on clinical research strategies and compared different adaptations by regulatory bodies and academic research institutions in a global context, exploring what can be learned for possible future pandemics. METHODS: We conducted a cross-sectional online survey and identified and assessed different COVID-19-specific adaptation strategies used by academic research institutions and regulatory bodies. RESULTS: All 19 participating academic research institutions developed and followed similar strategies, including preventive measures, manpower recruitment, and prioritisation of COVID-19 projects. In contrast, measures for centralised management or coordination of COVID-19 projects, project preselection, and funding were handled differently amongst institutions. Regulatory bodies responded similarly to the pandemic by implementing fast-track authorisation procedures for COVID-19 projects and developing guidance documents. Quality and consistency of the information and advice provided was rated differently amongst institutions. CONCLUSION: Both academic research institutions and regulatory bodies worldwide were able to cope with challenges during the COVID-19 pandemic by developing similar strategies. We identified some unique approaches to ensure fast and efficient responses to a pandemic. Ethical concerns should be addressed in any new decision-making process.

The beta-1,3-glucanosyltransferase gas4p is essential for ascospore wall maturation and spore viability in Schizosaccharomyces pombe.

Meiosis is the developmental programme by which sexually reproducing diploid organisms generate haploid gametes. In yeast, meiosis is followed by spore morphogenesis. The formation of the Schizosaccharomyces pombe ascospore wall requires the co-ordinated activity of enzymes involved in the biosynthesis and modification of its components, such as glucans. During sporogenesis, the beta-1,3-glucan synthase bgs2p synthesizes linear beta-1,3-glucans, which remain unorganized and alkali-soluble until covalent linkages are set up between beta-1,3-glucans and other cell wall components. Several proteins belonging to the glycoside hydrolase family 72 (GH72) with beta-1,3-glucanosyltransferase activity have been described in other organisms, such as the Saccharomyces cerevisiae Gas1p or the Aspergillus fumigatus Gel1p. Here we describe the characterization of gas4(+), a new gene that encodes a protein of the GH72 family. Deletion of this gene does not lead to any apparent defect during vegetative growth, but homozygous gas4Delta diploids show a sporulation defect. Although meiosis occurs normally, ascospores are unable to mature or to germinate. The expression of gas4(+) is strongly induced during sporulation and a yellow fluorescent protein (YFP)-gas4p fusion protein localizes to the ascospore periphery during sporulation. We conclude that gas4p is required for ascospore maturation in S. pombe.

The Schizosaccharomyces pombe endo-1,3-beta-glucanase Eng1 contains a novel carbohydrate binding module required for septum localization.

Cell separation in Schizosaccharomyces pombe is achieved through the concerted action of the Eng1 endo-beta-1,3-glucanase and the Agn1 endo-alpha-1,3-glucanase, which are transported to the septum and localize to a ring-like structure that surrounds the septum. Correct localization of these hydrolases requires the presence of both the septins and the exocyst. In this work, we show that the glucanase Eng1 contains a region at the C-terminus that acts as a carbohydrate-binding module (CBM) and that it is not present in other members of glycoside hydrolases family 81 (GH81). In vitro, the purified CBM has affinity for beta-1,3-glucan chains with a minimum degree of polymerization of 30 glucose units. Deletion of the CBM results in a protein that is largely defective in complementing the separation defect of eng1Delta mutants. This defect is due to a reduction in the catalytic activity against insoluble substrates and to a defect in targeting of Eng1 to the septum, as the truncated protein localizes to the lateral cell wall of the cell. Thus, the targeting of Eng1 to the primary septum requires not only trans-factors (septins and the exocyst complex) but also a cis-element localized to the C-terminus of the protein.

Characterization of the endo-beta-1,3-glucanase activity of S. cerevisiae Eng2 and other members of the GH81 family.

The GH81 family includes proteins with endo-beta-1,3-glucanase widely distributed in yeast and fungi, which are also present in plants and bacteria. We have studied the activity of the Saccharomyces cerevisiae ScEng2 and the Schizosaccharomyces pombe SpEng1 and SpEng2 proteins. All three proteins exclusively hydrolyzed linear beta-1,3-glucan chains. Laminari-oligosaccharide degradation revealed that the minimum substrate length that the three endoglucanases were able to efficiently degrade was a molecule with at least 5 glucose residues, suggesting that the active site of the enzymes recognized five glucose units. Prediction of the secondary structure of ScEng2 and comparison with proteins of known structure allowed the identification of a 404-amino acid region with a structure similar to the Clostridium thermocellum endoglucanase CelA. This fragment showed similar enzymatic characteristics to those of the complete protein, suggesting that it contains the catalytic domain of this family of proteins. Within this domain, four conserved Asp and Glu residues (D518, D588, E609, and E613) are necessary for enzymatic activity.

The spindle assembly checkpoint: clock or domino?

In each cell division, the newly duplicated chromosomes must be evenly distributed between the sister cells. Errors in this process during meiosis or mitosis are equally fatal: improper segregation of the chromosome 21 during human meiosis leads to Down syndrome (Conley, Aneuploidy: etiology and mechanisms, pp 35-89, 1985), whereas in somatic cells, aneuploidy has been linked to carcinogenesis, by unbalancing the ratio of oncogenes and tumor suppressors (Holland and Cleveland, Nat Rev Mol Cell Biol 10(7):478-487, 2009; Yuen et al., Curr Opin Cell Biol 17(6):576-582, 2005). Eukaryotic cells have developed a mechanism, known as the spindle assembly checkpoint, to detect erroneous attachment of chromosomes to the mitotic/meiotic spindle and delay the cell cycle to give enough time to resolve these defects. Research in the last 20 years, has demonstrated that the spindle assembly checkpoint is not only a pure checkpoint pathway, but plays a constitutive role in every cell cycle. Here, we review our current knowledge of how the spindle assembly checkpoint is integrated into the cell cycle machinery, and discuss some of the questions that have to be addressed in the future.

Expression, stability, and replacement of glucan-remodeling enzymes during developmental transitions in Saccharomyces cerevisiae.

Sporulation is a developmental variation of the yeast life cycle whereby four spores are produced within a diploid cell, with proliferation resuming after germination. The GAS family of glycosylphosphatidylinositol-anchored glucan-remodeling enzymes exemplifies functional interplay between paralogous genes during the yeast life cycle. GAS1 and GAS5 are expressed in vegetative cells and repressed during sporulation while GAS2 and GAS4 exhibit a reciprocal pattern. GAS3 is weakly expressed in all the conditions and encodes an inactive protein. Although Gas1p functions in cell wall formation, we show that it persists during sporulation but is relocalized from the plasma membrane to the epiplasm in a process requiring End3p-mediated endocytosis and the Sps1 protein kinase of the p21-activated kinase family. Some Gas1p is also newly synthesized and localized to the spore membrane, but this fraction is dispensable for spore formation. By way of contrast, the Gas2-Gas4 proteins, which are essential for spore wall assembly, are rapidly degraded after spore formation. On germination, Gas1p is actively synthesized and concentrated in the growing part of the spore, which is essential for its elongation. Thus Gas1p is the primary glucan-remodeling enzyme required in vegetative growth and during reentry into the proliferative state. The dynamic interplay among Gas proteins is crucial to couple glucan remodeling with morphogenesis in developmental transitions.

ß(1,3)-glucanosyl-transferase activity is essential for cell wall integrity and viability of Schizosaccharomyces pombe.

BACKGROUND: The formation of the cell wall in Schizosaccharomyces pombe requires the coordinated activity of enzymes involved in the biosynthesis and modification of ß-glucans. The ß(1,3)-glucan synthase complex synthesizes linear ß(1,3)-glucans, which remain unorganized until they are cross-linked to other ß(1,3)-glucans and other cell wall components. Transferases of the GH72 family play important roles in cell wall assembly and its rearrangement in Saccharomyces cerevisiae and Aspergillus fumigatus. Four genes encoding ß(1,3)-glucanosyl-transferases -gas1(+), gas2(+), gas4(+) and gas5(+)- are present in S. pombe, although their function has not been analyzed. METHODOLOGY/PRINCIPAL FINDINGS: Here, we report the characterization of the catalytic activity of gas1p, gas2p and gas5p together with studies directed to understand their function during vegetative growth. From the functional point of view, gas1p is essential for cell integrity and viability during vegetative growth, since gas1Δ mutants can only grow in osmotically supported media, while gas2p and gas5p play a minor role in cell wall construction. From the biochemical point of view, all of them display ß(1,3)-glucanosyl-transferase activity, although they differ in their specificity for substrate length, cleavage point and product size. In light of all the above, together with the differences in expression profiles during the life cycle, the S. pombe GH72 proteins may accomplish complementary, non-overlapping functions in fission yeast. CONCLUSIONS/SIGNIFICANCE: We conclude that ß(1,3)-glucanosyl-transferase activity is essential for viability in fission yeast, being required to maintain cell integrity during vegetative growth.