The stress response protein Hsp12p increases the flexibility of the yeast Saccharomyces cerevisiae cell wall.

The yeast S. cerevisiae cell wall comprising a 10 nm thick layer of polysaccharides, predominantly beta(1,3)-glucan and proteins, is the interface between the cell and the neighbouring environment. As such it is not a static entity but rather one that is dynamically remodelled in response to changes in the environmental conditions. We have recently proposed from studies using yeast cells lacking the gene encoding Hsp12p (Deltahsp12 yeast) and from incorporation of Hsp12p into agarose, used as a model system for the beta-glucan layer of the cell wall, that the hydrophilic stress response cell wall protein Hsp12p acts as a cell wall plasticizer. In this report we have used force spectroscopy to confirm that Deltahsp12 yeast are indeed less flexible than the wild type strain. The spring constant of the cell wall of Deltahsp12 yeast, kcw was determined to be 72+/-3 mN m-1 as compared to 17+/-5 mN m-1 obtained for the wild type strain. A similar result was found on the basis of a quantitative analysis of the electrophoretic mobilities measured for the two yeast strains. Those indicated that the hydrodynamic permeability quantified through the softness parameter of the external layer of Deltahsp12 cells was smaller than the one of wild type cells. We proposed from surface infrared spectroscopy measurements that yeast compensate for the lack of Hsp12p by reducing the carbohydrate/proteins ratio of the cell wall or increasing the cell wall chitin content.

A rapid method to determine the stress status of Saccharomyces cerevisiae by monitoring the expression of a Hsp12:green fluorescent protein (GFP) construct under the control of the Hsp12 promoter.

The gene for the green fluorescent protein (GFP) was fused in-frame to the 3' end of HSP12. This construct was regulated by the HSP12 promoter in a pYES2 yeast expression vector. No fluorescence was observed in yeast growing exponentially in glucose-containing medium, but fluorescence was observed when the yeast entered the stationary phase. Fluorescence microscopy indicated that the fusion protein was localized to the peripheral regions of the cell as well as to the cytoplasm and the tonoplast. Subjecting the yeast to a variety of stresses known to induce HSP12 transcription, including salt, osmotic, ethanol, and heat stress, resulted in a time-dependent increase in GFP fluorescence. The use of this system as a method to assess the general stress status of yeast growing in an industrial application is proposed.

Modulation of Congo-red-induced aberrations in the yeast Saccharomyces cerevisiae by the general stress response protein Hsp12p.

Previous studies have shown that in Saccharomyces cerevisiae HSP12, which codes for the small cell wall heat shock protein Hsp12p, was induced upon exposure to cell-wall-damaging agents such as Congo red. Here, we demonstrate that Hsp12p decreases the interaction between Congo red and chitin. A Deltahsp12 mutant strain displayed decreased viability, increased aggregation and sedimentation, as well as an altered morphology when grown in the presence of Congo red dye. The presence of Hsp12p was also necessary for the Congo-red-mediated invasion of agar plates.