Optimization of conditions for studies of protein unfolding by hydrogen exchange/mass spectrometry.

Understanding the forces driving protein folding and aggregation is an essential step in developing means for controlling these important processes. Amide hydrogen exchange, coupled with mass spectrometry, has become an important method for studying protein unfolding and refolding. To extend procedures developed to study unfolding of relatively soluble proteins to less soluble, aggregation-prone proteins requires special considerations. This publication describes a general strategy developed using yeast transaldolase, which aggregates easily under conditions required to study its unfolding. Results presented here show that reducing the protein concentration to the nanomolar range is essential for managing aggregation of transaldolase. In addition, the present results point to use of relatively high concentrations of denaturants and short incubation times to minimize aggregation. These results also show how amide hydrogen exchange, coupled with mass spectrometry, can be used to study soluble aggregates.