Localization of yeast cell wall mannoproteins - impact on wall biogenesis

Yeast cell wall contains proteins that are noncovalently (Scw-proteins), or covalently (Ccw-proteins) bound to beta-1, 3-glucan, the latter either through GPI-anchors and beta-1, 6-glucan, or by alkali labile ester linkages between gamma-carboxyl groups of glutamic acid and hydroxyl groups of glucoses (Pir-proteins, extracted from the cell wall by mild alkali). Disruption of all four genes coding for Pir-proetins revealed that 67 kDa protein still remained in the NaOH extract. Disruption of the SCW4, a gene coding for one of most abundant SCW proteins resulted in the disappearance of the band, indicating that Scw4p was partly also covalently linked to the cell wall by an apparently new, so far unobserved alkali sensitive linkage. Structural analysis revealed that N-terminal part of the protein is required for anchoring in the wall. Both the absence and the increased concentration of Scw proteins resulted in undesirable changes in the wall and in the increase in cell mortality, particulary upon entering the stationary growth conditions. Possibilities for application of the knowledge gained on different mechanisms for incorporation of wall proteins in heterologous expression of proteins in yeast and their ˝genetic immobilisation˝ will be discussed.