The influence of polyethyleneglycols on predicting crystallisation conditions of lipase from wheat germ by dynamic light scattering studies

The availability of lasers and the development of dynamic light scattering methods have led to a rebirth of the interest in light scattering applications in polymer sciences, biophysical chemistry and recently in biological macromolecules. In the case of these biomolecules, all the investigations have been focused on the crystallisation step, which is considered a handicap in protein crystallography, not only for the difficulties found in the search for crystallisation conditions, but also because little is known about crystal growth behaviour of protein molecules in solution [1] [L. Jancarik, S.H. Kim, J. Appl. Crystallogr., 24 (1991) 409] [2] [A. McPherson, Preparation and Analysis of Protein Crystals, Krieger, Malabar, FL, 1989, Chapter 4]. In this paper, the influence of polyethylene glycols ranging from polyethyleneglycol 400 to polyethyleneglycol 6000 molecular weight and of two alcohols (methanol and ethanol) on the aggregation steps of lipase from wheat germ at pH 6 and 9 has been studied in solution by the use of dynamic light scattering methods. It has been possible to evaluate whether the initial formation of clusters and the trend for aggregation is due to nucleation (crystal formation) or to random mechanisms (amorphous precipitate obtaining). Finally, it is shown how the experimental predictions are useful to design new experimental protocols in order to generate the first available nucleation of the protein studied, which will be grown by either macro or microseeding techniques.