Specific labelling of cell wall proteins by biotinylation. Identification of four covalently linked O-mannosylated proteins of Saccharomyces cerevisiae

Intact Saccharomyces cerevisiae cells were biotinylated with the non-permeable sulfosuccinimidyl-6-(biotinamido) hexanoate reagent. Twenty specifically labelled cell wall proteins would be extracted and visualized on SDS gels via streptavidin/horseradish peroxidase. Nine cell wall proteins were released by SDS extraction under reducing conditions and were designated Scw1-9p for (soluble cell wall proteins); five proteins were released from SDS-extracted cell walls by laminarinase (Ccw1-5p for covalently linked cell wall proteins) and six with mild (30 mM-NaOH, 4 degrees C, 14 h) alkali treatment (Ccw6-11p). N-terminal sequences of the Ccw proteins 6, 7, 8 and 11 showed that these cell wall proteins are members of the PIR gene family (predicted proteins with internal repeats), CCW6 being identical to PIR1 and CCW8 to PIR3. Single gene disruptions of all four genes did not yield a phenotype. In the CCW11 disruption the Ccw11p as well as the laminarinase-extracted Ccw5 protein was missing. The new cell wall proteins are O-mannosylated, contain a Kex2 processing site, but no C-terminal GPI anchor sequence.