STRUCTURE AND SOLUBILITY OF INTERLEUKIN-2 IN SODIUM DODECYL-SULFATE

The solubility of an interleukin-2 (C125A) in an aqueous sodium dodecy l sulfate (SDS) solution was examined as a function of SDS concentrati on. A stock interleukin-2 solution at 1.1 or 0.31 mg/mL was mixed with one-tenth volume of a stock SDS solution at various concentrations. A t intermediate SDS concentrations, the interleukin-2 showed nearly com plete precipitation, while lower or higher SDS concentrations resulted in an increase in protein solubility. Circular dichroic analysis indi cated that the protein remaining in the supernatant at low or high SDS concentrations has an altered conformation. Sedimentation velocity an alysis of interleukin-2 in 0.1% SDS showed that about half the protein was monomeric, with the remainder as large aggregates with a broad si ze distribution from 20 to 100 S (M(r) approximate to 10(5)-10(7)). In contrast, interleukin-2 in 0.01% SDS has a much smaller distribution of aggregates, sedimenting at ca. 2-10 S. (C) Munksgaard 1994.