Localisation and physiological role of saccharomyces cerevisiae cell wall proteins

Yeast cell wall is composed of about 85-90 % carbohydrate and the remaining 10-15 % protein. About half of the carbohydrate part of the wall is made of glucose organised in long unbranched chains in which monomeric units are linked by β-1,3-glycosidic linkages forming the structural fundament providing the required mechanical integrity and stability of the cell wall, thus fulfilling its major biological role. β-1,3-glucan serves also as a support for other molecules by which a yeast cell sees and feels its environment, most importantly for proteins. The cell wall of Saccharomyces cerevisiae contains a number of different mannoproteins. They are considered to play different roles in building, maintaining and modifying the wall itself through the life cycle. Besides, they are important for interactions of cells with their surrounding, the example of which are intercellular interactions during agglutination or flocculation. Cell wall proteins can be divided in three groups according to the mechanism by which they are attached to the wall. The first group of proteins is noncovalently connected to the cell wall structural polysaccharides and the identification of several members of this group showed that, most probably, they all possess enzymatic activities. The second group comprises proteins covalently attached to β-1,6-glucan, and they can be released from the wall by different glucanase preparations. Finally, a group of proteins can be extracted from the wall by 30 mmol L-1 NaOH but the actual link by which they are attached to the cell wall is unknown. In this review a survey of yeast cell wall proteins is made with an emphasis on our current knowledge of biochemical interactions involved in the incorporation of different groups of proteins into the wall.