Pressure is known to perturb both the inra- and intermolecular forces, effective between the polypeptide chains. Disrupted intramolecular interactions lead to the unfolding of the protein. This was characterized by several experimental methods1-2, and consistent thermodynamic description of the unfolding caused by either heat or pressure or cold is also available3.
A more sensitive system is the network of intermolecular interactions, which is stabilizing the quaternary structure of oligomers, or acting as driving force of aggregation and gel formation. Intermolecular interactions play also important role in the function of chaperone proteins, which prevent other proteins from irreversible aggregation.4
FTIR spectroscopy is sensitive for intermolecular antiparallel hydrogen bonding that results in the appearance of special infrared bands at the two sides of the amide I region5. These bands (at 1615 and 1685 cm-1) were followed in order to characterize the aggregation of the proteins.
We investigated several proteins including myoglobin, lipoxygenase, horseradish peroxidase, and ?-crystallin. This later protein is also known to have chaperoning effect. In all the cases pressure was found to destabilize the aggregates formed either spontaneously, or after temperature denaturation. It was also observed, that pressure unfolding does not cause intermolecular beta sheet type aggregates, but the pressure denatured protein is more aggregation prone after releasing the pressure. These aggregates were also pressure sensitive.
The ?-crystallin is special in the sense that its native form is already a big oligomer. Our experiments led to the conclusion, that pressure acting on these oligomers is able to affect the chaperoning ability of the protein as well. This underlines the importance of the pressure studies on the field of the molecular mechanism of the chaperoning effect.
1 Hayashi, R.; Balny, C.; High Pressure Bioscience and Biotechnology, ed.; Elsevier Science Publishers, Amsterdam, 1996.
2 Heremans, K.; Smeller, L. Biochim. Biophys. Acta (1998), 1386, 353-370.
3 S.A. Hawley, Reversible pressure-temperature denaturation of chymotrypsinogen, Biochemistry (1971) 10 2436.
4 Smeller, L.; Heremans, K. Biochemistry (1999) 38, 3816.
5 Ismail, A.A., Mantsch, H.H. and P.T.TWong. (1992) Biochim. Biophys. Acta 1121: 183.