Picosecond orientational dynamics of water in living cells

Abstract

Cells are extremely crowded, and a central question in biology is how this affects the intracellular water. Here, we use ultrafast vibrational spectroscopy and dielectric-relaxation spectroscopy to observe the random orientational motion of water molecules inside living cells of three prototypical organisms: Escherichia coli, Saccharomyces cerevisiae (yeast), and spores of Bacillus subtilis. In all three organisms, most of the intracellular water exhibits the same random orientational motion as neat water (characteristic time constants ~9 and ~2 ps for the first-order and second-order orientational correlation functions), whereas a smaller fraction exhibits slower orientational dynamics. The fraction of slow intracellular water varies between organisms, ranging from ~20% in E. coli to ~45% in B. subtilis spores. Comparison with the water dynamics observed in solutions mimicking the chemical composition of (parts of) the cytosol shows that the slow water is bound mostly to proteins, and to a lesser extent to other biomolecules and ions.

Is a constant low-entropy process at the root of glycolytic oscillations?

“…In fact, there is a long-standing controversy about the state of water in intact cells. While some reports suggest that most intracellular water is in a liquid state [15,16], others claim that it is altered, in an Hbonded polymer-based gel-like state [17][18][19][20]. Therefore, it is still an open question to what extent mass action kinetics is a valid framework on which to build a more complete understanding of the processes occurring in the cell cytoplasm.…”

Measuring ion-pairing and hydration in variable charge supramolecular cages with microwave microfluidics

“…Previous microwave (0.1 GHz to 100 GHz) dielectric spectroscopy studies of salt solutions have characterized the solventmediated ion pairing and hydration of ions in solution [18][19][20] . Bulkfluid dielectric spectroscopy can also measure hydration and ionic interactions in complex biomolecular systems including proteins, DNA, and cells [21][22][23] . Microwave-microfluidic measurements enable on-chip measurements for nanoliter fluid volumes over a wide frequency range (0.4 MHz-100 GHz).…”

Water in protein hydration and ligand recognition

“…Water supply is obviously crucial for a healthy organism, but the extent differs between species, and also between tissues. Under ideal conditions, the mass fraction of water in a cell ranges from the usual ~70% for, for example, human red blood cell or Escherichia coli , down to ~40% for Bacillus subtilis spores, which can endure extreme levels of heat, radiation, and chemicals . Some tardigrada , claimed to be the overall most resilient species on earth, can be dessicated to ~3% water content under slow drying conditions and still be revived.…”

“…Water becomes structured differently in the field of a protein: It has been found to be about 15% more dense on the surface of a protein than in the bulk phase . The cellular mixture results in a macroscopic viscosity of the cytoplasm that is similar to a gel, about ~10 6 times higher than pure bulk water …”

“…The maximum amount of “slow water” has been measured in Haloarcula marismortui by H‐NMR to be ~75%, but it was concluded that neither its proteins nor the high salt concentrations alone could account for this retardation . Most estimates range from ~10 to 20% of all cellular water in human red blood cells and Escherichia coli to ~45% in Bacillus subtilis spores . The calculated amounts differ since some experiments probe collective motions, while others probe individual molecules, and also assumptions for interpretation can vary .…”