Altered extent of cross-linking of beta 1,6-glucosylated mannoproteins to chitin in Saccharomyces cerevisiae mutants with reduced cell wall beta 1,3-glucan content

The yeast cell wall contains beta 1,3-glucanase-extractable and beta 1,3-glucanase-resistant mannoproteins. The beta 1,3-glucanase-extractable proteins are retained in the cell wall by attachment to a beta 1,6-glucan moiety, which in its turn is linked to beta 1,3-glutan (J. C. Kapteyn, R C. Montijn, E. Vink, J. De La Cruz, A. Llobell, J. E. Douwes, H. Shimoi, P. N. Lipke, and F. M. Klis, Glycobiology 6:337-345, 1996). The pl,3-glucanase-resistant protein fraction could be largely released by exochitinase treatment and contained the same set of beta 1,6-glucosylated proteins, including Cwp1p, as the beta 1,3-glucanase-extractable fraction. Chitin was linked to the proteins in the beta 1,3-glucanase-resistant fraction through a beta 1,6-glucan moiety. In wild-type cell walls, the beta 1,3-glucanase-resistant protein fraction represented only 1 to 2% of the covalently linked cell wall proteins, ,whereas in cell walls of fks1 and gas1 deletion strains, which contain much less beta 1,3-glucan but more chitin, beta 1,3-glucanase-resistant proteins represented about 40% of the total. We propose that the increased crosslinking of cell wall proteins via beta 1,6-glucan to chitin represents a cell mall repair mechanism in yeast, which is activated in response to cell wall weakening.