Glucan mannan-protein complex

A historical review of the development of our knowledge of the yeast cell wall was given by Phaff (I). Most information based on chemical studies has been derived, by far, from studies with cell walls from baker s yeast, Saccharomyces cerevisiae, and closely related species. The principal components of Saccharomyces walls are several types of glucan and a mannan-protein complex which may contain variable proportions of phosphate. A low content of chitin (ca. 1% ) may be present depending on the number of times a cell has produced buds. The reason for this is that chitin is present only in the bud scars (ca. 3 pm2 in area) produced on the surface of a mother cell (2), each at a different place on the cell surface. 

Yeasts are single-cell fungi with cell walls consisting of two interlocking structures, either of which is sufficient to keep the characteristic shape. One structure is made entirely of glucan (a poly-anhydride of glucose), and the other is a mannan—protein complex bound to disulfide linkages. Only when both structures are broken is the cytoplasm extruded (Bacon etaL, 1965). 

The best characterized component of the cell wall is the a-mannan [36] (Fig. 16.3). The molecule is made up of an inner core of a repeating a-(l-6) chain of mannose residues with short side chains of a-(l-2) and a-(l-3) linked residues. At the end of this inner core are two A-acetyl glucosamine residues (chitobiose) and the terminal one is attached to the carboxylic acid residue in the side chain of an aspartic acid residue of a protein. Attached to the opposite end of the inner core molecule is an outer chain of 100-150 mannose residues. This unit consists of an a(l-6) backbone with a(l-2) and a(l-3) side chains, some of which contain phosphodiester linkages. In addition to this complex molecule, and attached to the same protein via serine and threonine hydroxyl groups, are short a(l-2) and a(l-3) chains of mannose residues. Other observations on the structure of the wall reveal that glucan is also covalently... 

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