Adiabatic compressibility of globular proteins.

Abstract

The adiabatic compressibility of several globular proteins has been measured by using an ultrasonic technique in the frequency range 0.5 to 10 MHz. The contributions to the measured-compressibility from the protein matrix .and from surface processes involving ionization of side chains and solvation effects are discussed; The internal -protein compressibility is very. low, indicating the existence of "dynamic domains" which are tentatively assigned to secondary structure elements.During the past few years, considerableinterest in the problem of fast conformational fluctuations in protein systems has developed (1-3). Many techniques have been used to study fluctuations in biomolecules. Generally they involve the study of relaxational behavior after a perturbation is applied to the system-(4). The external perturbation can take the form of.a step or a continuous sinusoidal function. We have studied the behavior ofprotein systems under continuous-wave pressure perturbation. A pressure wave in a fluid causes alternating compressions and rarefactions. Because the period is short compared with the time required for thermal equilibrium of the solution, the process is reversible and adiabatic. By using pressure waves, one can extract information about mechanical and thermal properties of the system. The frequency dependence of these properties arises from relaxational processes, yielding valuable information on the time constants of the different mechanisms involved.The theory of pressure wave propagation in solutions can be found in standard texts (for instance, see ref. 5). The adiabatic compressibility is defined by Pad = -1/V (aV/aP)s where V is the volume of the sample and P is the pressure. Pad can be obtained by a measurement ofthe density p and sound velocity c. Pad = 1/pc2. For a solution containing protein, the protein adiabatic compressibility may be determined by measuring the density and sound velocity in the solution as afunction ofprotein concentration.Adiabatic compressibilities of protein solutions have been reported (6)(7)(8)(9)(10)(11). Quite recently this method has been applied to the study of the compressibility of cytochrome c in the oxidized and reduced forms (12). The reported values for apparent protein compressibility are generally low, on the order of 10-20% of the compressibility ofwater which is a relatively incompressible liquid. This low value is generally explained by the observation that the-constituent amino acids have a negative apparent compressibility. The apparent positive value observed for, globular proteins then reflects a very compressible protein interior (8).In order to explain the increase in compressibility upon denaturation, which seems to contradict the hypothesis of a high compressibility of the protein interior, a very high local concentration of nonpolar groups is assumed for a denatured protein. Sarvazyan and Hemmes (6) discussed the possible contribution ofrelaxations to the compressibility on the basis ofsound absorption data. However, no direct measurements...

Some thermodynamic implications for the thermostability of proteins

“…It is possible that the effects of volume changes on the energy of the native state could be offset by comparable effects on the denatured state. A direct analysis of this phenomenon appears problematic, however, because both ␣ and ␤ for the protein-solvent system change on denaturation in a protein-dependent fashion (Brandts et al 1970;Hawley 1971;Zipp and Kauzmann 1973;Gavish et al 1983;Prehoda et al 1998;Panick et al 1999) that has been difficult to generalize in terms of the relative consequences on (dE/ dV) T .…”

Pressure‐induced perturbation of ANS‐apomyoglobin complex: Frequency domain fluorescence studies on native and acidic compact states

“…They concluded that pressure alters both the relative substate populations and the functional properties of the individual substates and, thus, can produce large changes in the static and dynamic properties of a protein ensemble. The effect of pressure on protein structure also has been described in terms 121 of cavity reduction inside the protein matrix as well as changes in the hydration of mainly peripheral regions of the polypeptide chain (Heremans, 1982;Gavish et al, 1983;Nolting & Sligar, 1993;Silva & Weber, 1993;Cioni & Strambini, 1994;Jonas & Jonas, 1994).…”

Solvent effects on the molecular structures of crude gliadins as revealed by density and ultrasound velocity measurements

“…For example, the number of hydrophobic amino acids and the type of secondary structures are believed to contribute to the compressible properties of a protein (Gavish et al, 1983;Gekko and Hasegawa, 1986). However, the primary and secondary structures of proteins are poorly correlated with the compressible properties of different proteins (Gavish et al, 1983;Gekko and Yamagami, 1991;Dadarlat and Post, 2001). For instance, a high homology between hen egg lysozyme and bovine milk α-lactalbumin is found in the primary (45% homology) and the secondary (29-33%…”

“…When examining the structure of a protein molecule, a number of different structural levels are apparent (Gavish et al, 1983;Gekko et al, 1996). It would be expected that each of the various structural levels would affect the compressibility of the protein molecule.…”

“…According to the definition of compressibility, the compressibility coefficient, β, which is used more widely, can be defined as the pressure dependence of the relative volume (Gavish et al, 1983;Bloor et al, 1983;Cooper, 1984;Heremans and Smeller, 1998;Blandamer et al, 2001;Taulier et al, 2005):…”