The aggregation of cytochrome C may be linked to its flexibility during refolding

Abstract

Large-scale expression of biopharmaceutical proteins in cellular hosts results in production of large insoluble mass aggregates. In order to generate functional product, these aggregates require further processing through refolding with denaturant, a process in itself that can result in aggregation. Using a model folding protein, cytochrome C, we show how an increase in final denaturant concentration decreases the propensity of the protein to aggregate during refolding. Using polarised fluorescence anisotropy, we show how reduced levels of aggregation can be achieved by increasing the period of time the protein remains flexible during refolding, mediated through dilution ratios. This highlights the relationship between the flexibility of a protein and its propensity to aggregate. We attribute this behaviour to the preferential urea-residue interaction, over self-association between molecules.

Keywords: Fluorescence anisotropy; Molten globule; Protein aggregation; Protein flexibility; Protein refolding.

Fig. 1

Fluorescence anisotropy at 280 (diamond) and absorbance at 320 nm (solid line) of cytochrome C in 8 M urea refolded at 1:5 (a), 1:10 (b) and 1:25 (c) by dilution with 100 mM TRIS pH 10.6, to a final protein concentration of 6.4 × 10⁻⁵ M