Glycoside hydrolases and glucanosyl transferases in Schizosaccharomyces pombe

Maria de Median Redondo Encarnación Dueñas Santero Thierry Fontaine Evangelina Pablo-Hernando M. Luisa Alonso Núñez Javier Encinar del Dedo Jean Paul Latgé Francisco del Rey Iglesias Carlos R. Vázquez de Aldana

Author address: 

Inst. Microbiologí­a Bioquí­mica Dpto Microbiologí­a y Genética CSIC/Univ. Salamanca Edificio Departamental Plaza Doctores de la Reina 37007 Salamanca, Spain

Abstract: 

The S. pombe cell wall is composed of α -1,3-glucan, β -glucan (linear β -1,3- glucan, β -1,6-glucan and β -1,6-glucan-branched β -1,3-glucan) and α - galactomannans. The nascent β -1,3-glucan chains remain soluble until covalent linkages to other components of the cell wall are created by different transglycosidase enzymes. We have analyzed the role of proteins from GH families 5 and 72 during the life cycle of fission yeasts. In S. cerevisiae, C. albicans and Aspergillus proteins from family GH72 (Gas, Phr and Gel) have been shown to have β -1,3-glucanosyl transferase activity and all of them are attached to the membrane trough a glycosilphosphatydilinositol (GPI). A search of the S. pombe genome for proteins with sequence similarity to S. cerevisiae Gas1 indicated the existence of four proteins from this family. Three of them (gas1, gas2 and gas5) are periodically expressed during the cell cycle, while expression of the fourth (gas4) is strongly induced during sporulation. gas4916; mutants undergo normal meiosis but they fail to form mature spores. Gas4 localizes to the forespore membrane and it is essential for the formation of the sporulationspecific cell wall and for germination of the spores. During vegetative growth gas1 seems to be an essential gene, while mutants lacking gas2 had no apparent phenotype and gas5916; mutants showed thicker cell walls during growth at high temperatures. Using GFP fusions, the proteins have localized to the plasma membrane. The proteins have been expressed in Pichia and the activity has been analyzed in vitro. They also have β -1,3-glucanosyl transferase activity, but the main products of the reaction are different. S. pombe contains also three proteins from family GH5, named Exg1, Exg2 and Exg3. These genes are differentially expressed during the vegetative cycle, since exg1 expression periodically oscillates while exg2 and exg3 do not show any variations. In addition, exg2 is induced during the sporulation process. We have found that these proteins have a different fate in the cell, since Exg1 is secreted to the cell wall and culture medium, Exg2 is a transmembrane protein and Exg3 remains in the cytoplasm. In contrast to other members of this family in S. cerevisiae, the S. pombe Exg proteins are only active against β -1,6-glucans. Detailed characterization of the activity of Exg1 expressed and purified in Pichia indicated that this protein is an endo-
2007

abstract No: 

NULL

Full conference title: 

The First International Fungal / Plant Cell Wall Meeting
    • International Fungal / Plant Cell Wall Meeting 1st