The yapsins are a family of GPI-linked aspartyl proteases required for cell wall integrity in Saccharomyces cerevisiae.
Damian Krysan (1), Paula Magnelli (2), Claudia Abeijon (2), Robert Fuller (3)
(1) Pediatric Infectious Disease, University of Michigan, 1500 E. Medical Center Dr. Ann Arbor MI 48109-0244;
(2) Molecular and Cell Biology, Boston University School of Dental Medicine, 700 Albany St. Boston MA 02118;
(3) Bilogical Chemistry, University of Michigan, 1301 E. Catherine St., Ann Arbor MI 48109
In yeast, cell wall stress activates a program of signaling pathways that regulate genes involved in the biosynthesis of the cell wall. Herein, we demonstrate that cell wall biosynthesis is also dependent on the yapsins, a family of five GPI-linked aspartyl proteases. A strain lacking all five yapsins (5ypsdel) had phenotypes characteristic of defects in cell wall integrity (osmoremedial heat-sensitivity, caffeine, and congo red sensitivity). Of the single yapsin mutants, YPS1 and YPS7 appear to play prominent roles in cell wall integrity. Compositional analysis of the cell wall of 5ypsdel shows that it has significantly decreased amounts of both beta-1,3-and 1,6-glucan. The terminal MAP kinase of the cell wall integrity pathway (PKC1-MPK1 pathway), Mpk1p, is also constitutively activated in 5ypsdel, presumably as an adaptive response. Using a LacZ reporter construct, we have shown that YPS1 is induced during cell wall stress in a PKC1-MPK1-dependent fashion. The unique role of YPS1 in the cell wall integrity response is further supported by the fact that yps1del is sensitive to caffeine at 37oC while none of the other yapsin single mutants is affected. These results indicate that yapsin-mediated proteolysis represents a previously unrecognized mode of post-translation regulation in cell wall synthesis that plays an important role in controlling cell wall glucan homeostasis.
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