Biophysical properties of Saccharomyces cerevisiae and their relationship with HOG pathway activation. Eur Biophys J

Theoretical Biophysics, Humboldt University, Invaliden Str 42, 10115 Berlin, Germany.
Biophysics of Structure and Mechanism (Impact Factor: 2.22). 10/2010; 39(11):1547-56. DOI: 10.1007/s00249-010-0612-0
Source: PubMed


Parameterized models of biophysical and mechanical cell properties are important for predictive mathematical modeling of cellular processes. The concepts of turgor, cell wall elasticity, osmotically active volume, and intracellular osmolarity have been investigated for decades, but a consistent rigorous parameterization of these concepts is lacking. Here, we subjected several data sets of minimum volume measurements in yeast obtained after hyper-osmotic shock to a thermodynamic modeling framework. We estimated parameters for several relevant biophysical cell properties and tested alternative hypotheses about these concepts using a model discrimination approach. In accordance with previous reports, we estimated an average initial turgor of 0.6 ± 0.2 MPa and found that turgor becomes negligible at a relative volume of 93.3 ± 6.3% corresponding to an osmotic shock of 0.4 ± 0.2 Osm/l. At high stress levels (4 Osm/l), plasmolysis may occur. We found that the volumetric elastic modulus, a measure of cell wall elasticity, is 14.3 ± 10.4 MPa. Our model discrimination analysis suggests that other thermodynamic quantities affecting the intracellular water potential, for example the matrix potential, can be neglected under physiological conditions. The parameterized turgor models showed that activation of the osmosensing high osmolarity glycerol (HOG) signaling pathway correlates with turgor loss in a 1:1 relationship. This finding suggests that mechanical properties of the membrane trigger HOG pathway activation, which can be represented and quantitatively modeled by turgor.

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    • "In addition, there are mechanosensitive or 'stretch' channels and molecules which are implicated in osmosensing as a proxy, for example responding to swelling or shrinkage by stretching the lipid membrane bounding the cell or cell organelle (Poolman et al., 2002, 2004; Reiser et al., 2003; Schliess et al., 2007; Hammami et al., 2009; Schaber et al., 2010; Maathuis, 2011). Finally there are the molecules identified by genetic analysis such as vanilloid receptors (Liu et al., 2006; Cohen, 2007) and histidine kinases (Schumacher et al., 1997; Urao et al., 1999; Razani et al., 2003; Wohlbach et al., 2008; Meena et al., 2010) which have not been characterized mechanistically as primary receptors of stretch or osmotic pressure but may be the first components in a cell signalling cascade linked to them. "
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    • "In these cases, the cell wall is much stiffer than the cytoskeleton, and; therefore, E obtained with a Hertz-Sneddon analysis has no physical meaning. It is worth mentioning the recent work of Schaber et al. (2010) where the volumetric elastic modulus was determined to study yeast wall elasticity. However, the volumetric elastic modulus is also different than the elasticity of the wall (Wu et al. 1985), but simple models are available in the literature to convert it to a meaningful wall stiffness Eh, where h is the wall thickness (Saito et al. 2006). "
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    • "For instance, the ratio between cytoplasmic and nuclear Hog1-XFP residence can be easily determined and its dynamics can be monitored at single cell levels using microfluidic devices allowing rapid and precise changes in external osmolarity. These approaches allow the measurement of signalling kinetics and frequency dependence and the quantification of information capacity (Hersen et al., 2008; Mettetal et al., 2008; Muzzey et al., 2009; Schaber et al., 2010). "
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