Effects of spermine NONOate and ATP on protein aggregation: light scattering evidences

Regulating protein function in the cell by small molecules, provide a rapid, reversible and tunable tool of metabolic control. However, due to its complexity the issue is poorly studied so far. The effects of small solutes on protein behavior can be studied by examining changes of protein secondary structure, in its hydrodynamic radius as well as its thermal aggregation. The study aim was to investigate effects of adenosine-5'-triphosphate (ATP), spermine NONOate (NO donor) as well as sodium/potassium ions on thermal aggregation of albumin and hemoglobin. To follow aggregation of the proteins, their diffusion coefficients were measured by quasi-elastic light scattering (QELS) at constant pH (7.4) in the presence of solutes over a temperature range from 25°C to 80°C.

1) Spermine NONOate persistently decreased the hemoglobin aggregation temperature Tairrespectively of the Na+/K+ environment, 2) ATP alone had no effect on the protein's thermal stability but it facilitated protein's destabilization in the presence of spermine NONOate and 3) mutual effects of ATP and NO were strongly influenced by particular buffer ionic compositions.

The ATP effect on protein aggregation was ambiguous: ATP alone had no effect on the protein's thermal stability but it facilitated protein's destabilization in the presence of nitric oxide. The magnitude and direction of the observed effects strongly depended on concentrations of K+ and Na+ in the solution.