Protein Conformation

Adam Perriman, Mark Henderson, Stephen Holt^¥ and John White

^¥ Rutherford Appleton Laboratory, U.K.

The study of protein unfolding is essential to understanding the behaviour of proteins in biological systems. Studying protein denaturation provides valuable information on the mechanism of protein folding, as well as information on the structure-function relationship of proteins. Structurally, proteins are relatively fragile molecules and can be unfolded thermally, chemically or by pressure or pH changes. This effect of these denaturants on proteins adsorbed at the air-water interface has become our current focus (1).

We monitor the structural changes of proteins adsorbed at the air-water interface to nanometre resolution with reflectometry using x-rays and neutrons.  A recent example of our work is the structural distortions accompanying the denaturation of the globular protein hen egg white lysozyme at the air-water interface is represented in Figure 1.  We have used the protein layer thickness as 'the order parameter' to reveal the relative amounts of the unfolded and folded states of the protein as a function of temperature (2). This analytical protocol allows us to determine thermodynamic characteristics such as the enthalpy and temperature associated with the unfolding processes.

Fig.1    Fraction of unfolded lysozyme vs temperature

 

1. Holt, S.A., McGillivray, D.J., Poon, S., White, J.W., J.Phys.Chem B, 2000, 104, 7431-7438.

2. Holt, S.A. , Henderson, M.J., White, J.W., Aust J. Chem., 2002, 55, 449-459.