Importance of Non-Covalent Interactions in Yeast Cell Wall Molecular Organization

Abstract

This review covers a group of non-covalently associated molecules, particularly proteins (NCAp), incorporated in the yeast cell wall (CW) with neither disulfide bridges with proteins covalently attached to polysaccharides nor other covalent bonds. Most NCAp, particularly Bgl2, are polysaccharide-remodeling enzymes. Either directly contacting their substrate or appearing as CW lipid-associated molecules, such as in vesicles, they represent the most movable enzymes and may play a central role in CW biogenesis. The absence of the covalent anchoring of NCAp allows them to be there where and when it is necessary. Another group of non-covalently attached to CW molecules are polyphosphates (polyP), the universal regulators of the activity of many enzymes. These anionic polymers are able to form complexes with metal ions and increase the diversity of non-covalent interactions through charged functional groups with both proteins and polysaccharides. The mechanism of regulation of polysaccharide-remodeling enzyme activity in the CW is unknown. We hypothesize that polyP content in the CW is regulated by another NCAp of the CW-acid phosphatase-which, along with post-translational modifications, may thus affect the activity, conformation and compartmentalization of Bgl2 and, possibly, some other polysaccharide-remodeling enzymes.

Keywords: acid phosphatase; cell wall; non-covalent interactions; polyphosphates; polysaccharide-remodeling enzymes; proteins; yeast.

Figure 1

Functions of inorganic polyphosphates on yeast cell surface: hypothetical scheme. PolyP—polyphosphates, CW—cell wall, PPS—periplasmic space, PM—plasma membrane, EV—extracellular vesicles, SV—secretory vesicles, ER—endoplasmic reticulum, AP—acid phosphatase Pho3, Bgl2—blue bow, Pi—orthophosphate, Man_np—mannosylated proteins, Me⁺⁺—divalent metal ions. Some yeast have a capsule on their surface, which is depicted on part of the CW surface.