The role of Kex2p and yapsins in the proteolytic processing of Scw4p in the Saccharomyces cerevisiae cell wall

Yeast cell wall contains proteins that are noncovalently (Scw- proteins) or covalently (Ccw-proteins) bound to β-1, 3-glucan, the latter either through GPI-anchors and β-1, 6-glucan, or by alkali labile ester linkages between γ-carboxyl groups of glutamic acid and hydroxyl groups of glucoses (Pir-proteins, extracted from the cell wall by mild alkali). It was previously shown that one of the most abundant Scw protein, Scw4p is partly also covalently linked to the cell wall. In this work it was shown that part of Scw4p underwent the proteolytic processing resulting in two forms of the protein in the cell wall. The proteolytic enzymes which might have a role in processing of Scw4p are Kex2p and a family of aspartic proteases called yapsins. To get a better insight in the processing of Scw4p, kex2 yeast strain and strain with all yapsin genes disrupted (5yps∆) were used. Scw4p was overproduced in these strains and Scw4p processing was examined.