Growth, Differentiation and Sexuality

78 J.P. Latgé and R. Calderone
Fig. 5.4. The cell wall polysaccharides of Saccharomyces cerevisiae and Aspergillus fumigatus, showingacentralcoreof
β1,3 glucan-chitin which is common to both organisms
The fibrillar, alkali-insoluble glucan complex is
embedded in an alkali-soluble amorphous cement
whose composition varies with fungal species, and
has been accordingly less studied. Moreover, the
alkali solubility of the extracted fraction is not associated
with a specific polysaccharide composition.
In Aspergillus and Schizosaccharomyces, itis
composed of α1,3/1,4 glucan and galactomannan
with galactopyranose in S. pombe or galactofuranose
in A. fumigatus (Bobbitt and Nordin 1978;
Beauvais et al. 2004; Sugawara et al. 2004; Grün
et al. 2005; Morelle et al., unpublished data). By
contrast, in S. cerevisiae, it is composed of complex
mannans and branched β1,3/1,6 glucan with β1,6
glucan side chains similar in organisation to that
in the alkali-insoluble fraction and without crosslinking
to chitin (Manners et al. 1973a,b; Hartland
et al. 1994).
Proteins are also part of the alkali-soluble fraction,
since they are solubilized and destroyed by
alkali. In contrast to polysaccharides which are
the major component of the cell wall, proteins are
present in minute amounts only. Cell wall proteins
are either in transit in the cell wall before being
secreted or part of the cell wall structure: S-S proteins
are released by reducing agents, GPI-CWPs by
hydrofluorhydric acid, and PIR proteins (protein
with internal repeats) by 30 mM sodium hydroxide
(Fleet 1991; Kapteyn et al. 1997, 2000; Moukadiri
and Zueco 2001; Castillo et al. 2003). However,