The contribution of the O-glycosylated protein Pir2p/Hsp150 to the construction of the yeast cell wall in wild-type cells and β1,6-glucan-deficient mutants

Abstract

The cell wall of yeast contains a major structural unit, consisting of a cell wall protein (CWP) attached via a glycosylphosphatidylinositol (GPI)-derived structure to β1,6-glucan, which is linked in turn to β1,3-glucan. When isolated cell walls were digested with β1,6-glucanase, 16% of all CWPs remained insoluble, suggesting an alternative linkage between CWPs and structural cell wall components that does not involve β1,6-glucan. The β1,6-glucanase-resistant protein fraction contained the recently identified GPI-lacking, O-glycosylated Pir-CWPs, including Pir2p/Hsp150. Evidence is presented that Pir2p/Hsp150 is attached to β1,3-glucan through an alkali-sensitive linkage, without β1,6-glucan as an interconnecting moiety. In β1,6-glucan-deficient mutants, the β1,6-glucanase-resistant protein fraction increased from 16% to over 80%. This was accompanied by increased incorporation of Pir2p/Hsp150. It is argued that this is part of a more general compensatory mechanism in response to cell wall weakening caused by low levels of β1,G-glucan.