Role of NaOH-extractable cell wall proteins Ccw5p, Ccw6p, Ccw7p and Ccw8p (members of the Pir protein family) in stability of the Saccharomyces cerevisiae cell wall.

The Saccharomyces cerevisiae cell wall contains more than 20 identified mannoproteins. Some of them can be released from the wall by hot SDS/mercaptoethanol treatment and are, therefore, considered as disulphide-linked or non-covalently attached to wall structural components. A number of covalently linked cell wall proteins are released after SDS extraction. They can be divided into these extractable by glucanases and those which can be released with 30 mM NaOH. The SDS-extractable proteins either possess enzymatic activities or are homologues of enzymes, mainly glucanases. Nothing is known, however, about the function of covalently linked proteins. In order to investigate the role of NaOH-extractable cell wall proteins, genes encoding all four identified members of this family of Pir proteins, CCW5, CCW6, CCW7 and CCW8, were disrupted and the phenotype of the mutants obtained was examined. They grew somewhat more slowly, were larger and irregularly shaped, and showed pronounced susceptibility to cell wall synthesis inhibitors like Calcofluor white and Congo red. In addition, the triple and the quadruple deletants had a decreased mating ability. All these properties were more obvious the more of these genes were disrupted, indicating that probably all members of this protein family are at least functionally equivalent in the cell wall.