Link between the hydration enthalpy of lysozyme and the density of its hydration water: Electrostriction

Abstract

Hydration shells around proteins in solution are on average denser than bulk water. Variations in enthalpy are observed during hydration/dehydration of proteins. To explain consistently those phenomena, a common mechanism-electrostriction-underlying the mechanical and contributing to thermal effects is proposed. The mean mass density of the hydration shell of lysozyme derived from the neutron and X-ray scattering is explained as following the compression of water in the fields of the order of 10(9) V m(-1) due to the charged sites at the boundary of the protein. The mean enthalpy of mixing ΔH(mean) of lysozyme in water calculated on the basis of the measured mean mass density falls in the middle of the values of the enthalpy of mixing ΔH(mix) observed in sorption experiments. This testifies that ΔH(mix) is due in part to the work done by the electrostriction pressure in hydration shell regions situated in high electric fields. The dependence of the sorption enthalpy of exemplary proteins on the number of adsorbed H(2)O molecules is also described in terms of electrostriction.

SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell

“…NMR and neutron spectroscopy have revealed altered mobility of water molecules on protein surfaces with respect to the bulk (11)(12)(13)(14)(15), and time-resolved vibrational spectroscopy has revealed distinctive dynamics of solvation near the active sites of enzymes during catalysis with respect to bulk solvent (16). Increased water density in the first hydration shell (HS), as well as surface-specific differences in the organization of the hydration water, have been reported by MD simulations (17)(18)(19)(20) and have been described thermodynamically in terms of electrorestriction (21). MD studies involving nucleic acids (7,22,23) or proteins (24,25), as well as anomalous x-ray solution studies on proteins and nucleic acids (26,27), have revealed the specific recruitment of ions into their HSs.…”

On the origin of the phase–space diffusion limit in (dis)ordered protein aggregation

“…The compaction of the hydration layer, when effectively carried out up to ca. 0.7 nm of the layer width, may lead to electrostriction effects, causing to switch on an electrostatic (polarization) potential, likely of the order of a fraction of mV per biomolecule length; for lysozyme one may speak of about 3 nm [23,26,33]. The so-described effect, according to Ref.…”

“…According to our previous considerations [29] and arguments provided in Refs. [26,33] it is legitimate to argue that such l diff can also naturally be approximated by a half-width of the eDL circumventing the crystal/aggregate. Eq.…”

“…The growing rule, Eq. (5), is inevitably associated with an entropy production [42] within the ionic-matter aggregating and decisively temperature dependent system [33,43,26,25]. The aqueous inhomogeneous lysozyme solution within dVrealm, equivalent to the inner part of the eDL, the width of which being l diff , is clearly an entropic viz energy-dissipating system, cf.…”

“…It seems that such an effect is inevitably present in creating the ordering of biomolecules and water dipoles in the crystal surface layer [24]. When such changes come from a respective number of the biomolecules and water dipoles they may constitute a local thermal gradient, imposing the actual ordering direction for the dipoles [25,26], and influencing both the entropy production at the crystal surface, and at least, a local (radially measured) crystal growth rate [1,27]. …”