The molecular stoichiometric hydration model (SHM) as applied to tendon/collagen, globular proteins and cells

Abstract

This report describes and documents the presence of multiple water-of-hydration fractions on proteins and in cells. Initial studies of hydration fractions in g of water/g of DM (dry mass) for tendon/collagen led to the development of the molecular SHM (stoichiometric hydration model) and the development of methods for calculating the size of hydration fractions on a number of different proteins of known amino acid composition. The water fractions have differences in molecular motion and other physical properties due to electrostatic interactions of polar water molecules with electric fields generated by covalently bound pairs of opposite partial charge on the protein backbone. The methods allow calculation of the size of four hydration fractions: single water bridges, double water bridges, dielectric water clusters over polar-hydrophilic surfaces and water clusters over hydrophobic surfaces. These four fractions provide monolayer water coverage. The predicted SHM hydration fractions match closely measured hydration fraction values for collagen and for globular proteins. This report also presents water sorption findings that support the SHM. The SHM is applicable for cell systems where it has been studied. In seven cell systems studied, more than half of all of the cell water had properties unlike those of bulk water. The SHM predicts and explains the commonly cited and measured bound water fraction of 0.2-0.4 g of water/g of DM on proteins. The commonly accepted concept that water beyond this bound water fraction can be considered bulk-like water in its physical properties is unwarranted.

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“…As discussed above (Cameron and Fullerton, 2008) the prevailing dogma among physiologists and cell biologists is that all but a small fraction of cell water (estimated to be in the range of 0.2 to 0.4 g water/g dry mass) is bulk or bulk-like in its physical properties. Opposition to this dogma has come from a number of scientists including Pollack and Clegg 2008, Cameron and Fullerton 2011, Ling 2006, Mentré 2001, 2012.…”

“…A molecular stoichiometric hydration model (SHM) is presented that explains the four observed and measured monolayer water of hydration fractions on tendon collagen (Fullerton et al 2006 a , Fullerton andCameron 2007). This SHM has been shown applicable to globular proteins and to cells (Cameron et al 2011). The extent of nonbulk water has been found to increase during protein unfolding and decrease during protein aggregation (Fullerton et al 2006).…”

“…The presence and extent of multiple water of hydration fractions on proteins and in cells has been a subject of debate (Ball 2008, Pollack and Clegg 2008, Fullerton and Cameron 2007, Cameron and Fullerton 2008, Cameron, Lanctot and Fullerton 2011. The physical characteristics and size of multiple water of hydration fractions has been measured on tendon/collagen by water proton NMR spin-lattice relaxation at different levels of collagen hydration (Fullerton et al 2006).…”

Translational and Rotational Dynamics of Water Molecules in Aligned Collagenous Tissues: Implications for Assessing Collagen Organisation with Magnetic Resonance Imaging

“…A summary of the research into collagen hydration, by Fullerton, can be found in [53]. Based on the hydrations calculated from NMR titration experiments [146] of tendon, Cameron and Fullerton [145] developed the Stoichiometric Hydration Model (SHM), which predicts one single and one double water bridge for every tripeptide unit in the tropocollagen molecule.…”

“…Eight different water bridge types were identified [142], and are described in Figure 8. The work of Fullerton and colleagues [33,53,[143][144][145] has focused on a specific type of bridge; an inter-chain water bridge between the carboxyl oxygen …”