Hydration Study of Globular Proteins by Microwave Dielectric Spectroscopy

Abstract

A microwave dielectric measurement was performed to study the hydration properties of proteins in solution with a precision network analyzer with high reproducibility within the errors of 0.02 in relative dielectric constant over 2 to 10 GHz. A measurement was carried out for catalase, chymotrypsinogen A, cytochrome C, hemoglobin, peroxidase, lysozyme, myoglobin, ovalbumin, and bovine serum albumin at 20.0 ( 0.01 °C. The hydration properties of protein molecules were evaluated based on the Wagner mixture theory combined with single Debye approximation to the complex dielectric constant of hydrated solutes in the above frequency range. This was used to evaluate the loosely bound water number N w from the single Debye fitting, which gives the relaxation frequency (f c ) of the hydration shell loosely bound and tightly bound water number N s with lower relaxation frequencies than f c . Those hydration numbers were compared with the monolayer water numbers accessible to hydrophobic and hydrophilic exposed atoms, respectively, obtained from the calculation of accessible surface area of each protein structure based on the protein database. The result showed a good agreement both in the ratio and numbers. * To whom correspondence should be addressed. ap * ) a *{2(1φ) a * + (1 + 2 φ) q *}/{(2 + φ) a * +(1φ) q *} (1)

Role of Water in Actin–Myosin Binding and Actin Polymerization: Rotational and Translational Mobility of Water Molecules

“…Those f c values are equivalent to DR times ( diel ) of 40 ps ( diel = 1/2 f c ) and lower than the reported value of f cw for bulk water 17 GHz ( diel = w = 1/2 f cw = 9.36 ps) at 20 °C, which corresponds to the cooperative orientation motion of water molecules [9]. In addition, the number of hydrating water molecules per protein molecule (N total ) calculated from the dielectric exclusion volume agrees well with an estimate based on the solvent-accessible surface area (N ASA ) [8]. The data also yielded an averaged value of weight-based hydration (0.3-0.4 g/g protein), which falls within the range of values for various proteins estimated by other methods [2][3][4][5][6][7][8][9][10].…”

“…We recently developed a method of measuring the total volume of water molecules affected by proteins in solution (dielectric exclusion volume or hydration shell volume) and their dielectric relaxation (DR) frequency f c , which is referred to as the rotational mobility of hydration water molecules. For the globular proteins examined so far, the estimated f c values of hydrating water were around 4 GHz [7][8]. Those f c values are equivalent to DR times ( diel ) of 40 ps ( diel = 1/2 f c ) and lower than the reported value of f cw for bulk water 17 GHz ( diel = w = 1/2 f cw = 9.36 ps) at 20 °C, which corresponds to the cooperative orientation motion of water molecules [9].…”

Hydrogen Bond Network of Water around Protein Investigated with Terahertz and Infrared Spectroscopy

“…Assuming albumin aqueous solution to be a three-body model with a spherical soluteε sol ðuÞ covered by a concentric shell of hydration waterε hyd ðuÞ, which is uniformly distributed in a continuous bulk water mediumε bulk ðuÞ, the complex dielectric constant of albumin aqueous solution is replicated by the following Wagner equation (27,29,108):…”

“…Molecular dynamics (MD) simulations (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and other experimental approaches (23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37) have revealed the protein is surrounded by dynamically retarded hydration water, with the innermost shell having a density higher than that of bulk water. However, even today, experimentally characterizing the dynamics and the structure of the water HB network in this hydration shell is challenging, because the water-water HB lifetime is very short (typically 1 ps) (38).…”

Characterization of Dielectric Responses of Human Cancer Cells in the Terahertz Region

“…However, these rotational dynamics of hydrated water in the vicinity of a biomolecule are retarded to a nanosecond timescale. Conventional NMR [19] and microwave dielectric spectroscopy [21,22] can detect such retarded hydrated water dynamics, but are insensitive to the majority fraction, the bulk water, which have motional dynamics from a picosecond to sub-picosecond timescale. It is only recently that terahertz (THz) spectroscopy, which can measure the picosecond and subpicosecond dynamics associated with water, has become available [23][24][25][26][27].…”