3 Biogenesis of Yeast Wall and Surface Components

Abstract

I. INTRODUCTION
The cell wall preserves the osmotic integrity of Saccharomyces cerevisiae and defines the morphology of the yeast cell during budding growth and during the developmental processes of mating, sporulation, and pseudohypha formation. The approximately 200-nm-wide wall endows the cell with osmotic stability and is also the framework to which biologically active proteins such as cell adhesion molecules or hydrolytic enzymes are attached or within which they act. The wall makes up 15–30% of the dry weight of the vegetative cell, and its major components, by weight, are mannoproteins (40%) and β-1,3 and (β-1,6 glucans (50–60%). Chitin makes up 1–2% of the wall and is found mostly in the division septum. Some surface glycoproteins also receive a glycosyl phosphatidylinositol (GPI) membrane anchor. The plasma membrane is enriched in inositol phosphoceramides, which are cotransported to the cell surface with GPI-anchored proteins.

Yeast cell wall biogenesis is fascinating in its own right as an example of cellular morphogenesis, since the wall must expand during cell growth and a division septum must be synthesized at a specific time and place in the cell division cycle. Furthermore, yeast has proven to be a rewarding model system in which to explore biosynthetic pathways that are obviously conserved among eukaryotes, such as asparagine-linked glycosylation. However, it is emerging that seemingly specialized aspects of yeast wall biogenesis also have their parallels in other organisms. Thus, chitin-synthase-related proteins are present both in rhizobia and in vertebrates, the pathway leading to β-1,6 glucan assembly recalls...