The retention mechanism of cell wall proteins in Saccharomyces cerevisiae. Wall-bound Cwp2p is β-1,6-glucosylated

It has been proposed that the cell wall proteins of Saccharomyces cerevisiae are anchored by means of a β-1,6-glucose-containing side chain. Recently, we have identified three cell wall mannoproteins. Two of these mannoproteins are recognized in their cell wall bound form by an antiserum raised against β-1,6-glucan but the third, Cwp2p, is not. This could indicate the existence of alternative retention mechanisms for cell wall proteins. Western analysis of a fusion protein consisting of Cwp2p and the reporter enzyme α-galactosidase revealed that this protein is glycosyl phosphatidylinositol-anchored in the intracelullar precursor form and is recognized by an anti β-1,6-glucan antiserum in the cell wall bound form. The cell wall bound forms of fusion proteins consisting of the anchor regions of Sed1p or Flo1p and α-galactosidase were also recognized by an anti β-1,6-glucan antiserum. This is consistent with the existence of a general anchoring mechanism of proteins to the cell wall by means of a β-1,6-glucose-containing carbohydrate chain. Western analysis of a yeast strain producing c-myc epitope tagged Cwp2p revealed that this protein is only detectable if fatty acid chains are present on the protein, indicating that the lack of recognition of Cwp2p by an anti β-1,6-glucan antiserum is caused by a blotting artefact of the mature protein.