Download Proteins are biopolymers construced from similar building blocks

High pressure effects on proteins. Elastic and nonelastic structural changes.
L. Smeller
Semmelweis University, Dept. Biophysics and Radiation Biology
Budapest Puskin u. 9. PF 263 H-1444 Hungary
Proteins are biopolymers construced from similar building blocks called amino acids. The
unique feature is that these polypeptide chains are folded in a certain three-dimensional
structure (called native structure), which enables them to perform their biological funtion.
Studies on protein structure and function by wide range of experimental techniques agree in
the fact that the native structure is only stable in a limited pressure-temperature range [1].
This fact can be described theoretically by the so-called elliptic phase diagram [2].
The pressure induced changes in proteins have clearly nonlinear character. The simplest
approach is to divide the pressure scale to several ranges where the effect of pressure can be
qualitatively different. High pressure (typically 5-10 kbar) will change the three dimensional
structure of the protein drastically, resulting in a loss of biological function. The molecule
undergoes nonelastic structural alteration under high pressure. This phase transition is called
pressure unfolding. Experimental evidences of pressure unfolding will be presented for
several proteins.
The most interesting region is below the unfolding pressure, where the changes of the
conformation are elastic, and mostly reversible. These reversible compressions are nonlinear,
because proteins can contain several domains, with different compressibility. The
compressibility of horseradish peroxidase (a heme protein) was measured in the low and high
pressure region [3,4]. The compressibility is calculated from an optical signal (fluorescence)
which is emitted by the porphyrin molecule inside the protein. This signal is perturbed by the
protein surrounding the chromophore. Compression of the protein increases this perturbation,
which allows the calculation of the compressibility.
The nonlinear elasticity is explained by existence of soft and rigid domains in the molecule.
During the compression these domains give important contribution at different pressure
ranges.
1 Heremans, K. and L. Smeller. (1998) Protein Structure and Dynamics at High Pressure Biochim. Biophys.
Acta 1386 353-370.
2 L. Smeller (2002) Pressure-temperature phase diagram of biomolecules Biophys. Biochim. Acta 1595 1129.
3 Balog, E., K. Kis-Petik, J. Fidy, M. Köhler, and J. Friedrich, 1997. Interpretation of multiple (0,0) bands in
the absorption spectrum of Mg mesoporphyrin embedded in horseradish peroxidase. Biophys. J. 73:397-405.
4 Smeller, L. and Fidy, J. (2002) The enzyme, horseradish peroxidase is less compressible at higher pressures
Biophys J. 82, 426-436.