Functional analyses of the extra‐ and intracellular domains of the yeast cell wall integrity sensors Mid2 and Wsc1

Abstract

Cell wall integrity signalling in Saccharomyces cerevisiae provides a model for the regulation of fungal wall biosynthesis. Chimers of the major plasma membrane sensors Wsc1 and Mid2 fused to GFP have been employed to show that intracellular and membrane distribution is only dependent on a membrane-anchored cytoplasmic tail. Phenotypic analyses of chimeric sensors in an isogenic Dmid2 Dwsc1 double deletion strain indicate that this tail, provided that it is linked to an extracellular domain, also determines the cellular response to different surface stresses to a large extent.

Together we are strong—cell wall integrity sensors in yeasts

“…Early studies confirmed their plasma membrane localization and suggested that Wsc1-GFP localizes to sites of cell wall remodelling [7,39,55]. This was confirmed by studies showing the accumulation of Wsc1-GFP in growing buds and, later on, at the bud neck during cytokinesis, with a constant redistribution of the sensor between the plasma membrane and internal compartments [51]. In contrast, Mid2 forms a patchy, largely immobile network throughout the plasma membrane in vegetatively growing yeast cells.…”

“…It was proposed that Wsc1 would act primarily during vegetative growth, whereas Mid2 would be more involved in the mating response, with some functional overlap [42]. This hypothesis was substantiated by the observed sensor distributions described above, with Wsc1-GFP dynamically localizing to sites of cell wall construction and Mid2-GFP moving into the shmoo-tip during mating [19,51]. Further hints for the structural basis of sensor specificity and dynamics were obtained from studies of chimeric proteins and the comparison to the homologous sensors from K. lactis.…”

“…Further hints for the structural basis of sensor specificity and dynamics were obtained from studies of chimeric proteins and the comparison to the homologous sensors from K. lactis. The ability of hybrid sensors (which had their extracellular regions exchanged between Wsc1 and Mid2) to complement the various phenotypes of a wsc1 mid2 double deletion strain indicated that a large part of the specific responses to extracellular stresses is mediated by the cytoplasmic tail [51]. On the other hand, heterologous complementation studies of the sensors from K. lactis in S. cerevisiae, and vice versa, showed that the extracellular regions are responsible for species specificity [45].…”

“…Using hybrid Wsc1/Mid2-GFP fusion constructs, in which the extracellular regions were switched, it was demonstrated that the cytoplasmic domains (with the TMD attached) determine the dynamics and the plasma membrane distribution of the sensors in S. cerevisiae [51]. The dynamic behaviour of Wsc1 further depends on a clathrin-mediated endocytosis, conferred by an NPFDD sequence in its cytoplasmic tail [40].…”

Microcompartments within the yeast plasma membrane

“…A similar example of microcompartmentation within the yeast plasma membrane is the punctuated and sometimes polarized distribution of the CWI (for c ell w all i ntegrity) sensors (Straede and Heinisch , 2007 ). In brief, the CWI-m itogen a ctivated p rotein k inase (MAPK) signaling pathway is triggered by stress at the yeast cell surface (either at the cell wall or at the plasma membrane), which is recognized by a five-membered family of transmembrane sensors (namely, Wsc1 to Wsc3, Mid2, Mtl1; Figure 2 ) (reviewed in Jendretzki et al , 2011 ).…”