THE RETENTION MECHANISM OF CELL-WALL PROTEINS IN SACCHAROMYCES-CEREVISIAE - WALL-BOUND CWP2P IS BETA-1,6-GLUCOSYLATED

It has been proposed that the cell wall proteins of Saccharomyces cere visiae are anchored by means of a beta-1,6-glucose-containing side cha in. Recently, we have identified three cell wall mannoproteins. Two of these mannoproteins are recognized in their cell wall bound form by a n antiserum raised against beta-1,6-glucan but the third, Cwp2p, is no t. This could indicate the existence of alternative retention mechanis ms for cell wall proteins. Western analysis of a fusion protein consis ting of Cwp2p and the reporter enzyme alpha-galactosidase revealed tha t this protein is glycosyl phosphatidylinositol-anchored in the intrac ellular precursor form and is recognized by an anti beta-1,6-glucan an tiserum in the cell wall bound form. The cell wall bound forms of fusi on proteins consisting of the anchor regions of Sed1p or Flo1p and alp ha-galactosidase were also recognized by an anti beta-1,6-glucan antis erum. This is consistent with the existence of a general anchoring mec hanism of proteins to the cell wall by means of a beta-1,6-glucose-con taining carbohydrate chain. Western analysis of a yeast strain produci ng c-myc epitope tagged Cwp2p revealed that this protein is only detec table if fatty acid chains are present on the protein, indicating that the lack of recognition of Cwp2p by an anti beta-1,6-glucan antiserum is caused by a blotting artefact of the mature protein.