engleski

S. cerevisiae Cell Wall Proteins

Yeasts communicate with their environment through their cell wall composed of a ß-1, 3-glucan network to which some chitin and a number of mannoporteins are attached. Some of the cell wall proteins are linked to the glucan backbone noncovalently, and can be extracted by SDS or DTT. Covalently linked wall proteins can be devided according to their localisation mechanism in two groups. The first group can be extracted from purified cell walls using different glucanase preparations. Identification of nine proteins of this group has shown that they all posses C-terminal signal for the attachment of the GPI-anchor. The second group of proteins was obtained by an extraction of walls with 30 mM NaOH. Four proteins of this group were identified by N-terminal sequencing and they were found to be members of the same, so called PIR protein family having several common structural features. All four proteins contain characteristic repetetive sequence at the N-terminal end, they are extensively O-glycosylated and do not posses the signal for the addition of GPI-anchor. Therefore, they must be incorporated into the cell wall by another molecular mechanism. To investigate which part of Pir proteins is responsible for their attachment to the cell wall, Ccw5p was used as a model. The protein was tagged with the haemagglutinin tag at the C-terminal end, and different deletions of the CCW5 gene were analysed. It was found that the protein lacking one repetitive unit was still attached to the cell wall but if both copies were deleted, the protein was secreted into the medium. This strongly suggests that Pir proteins are attached to the carbohydrate network of the wall via their repetitive sequence.

S. cerevisiae cell wall; Pir proteins

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