PHASE-SEPARATION ANALYSIS OF RECOMBINANT INTERLEUKIN-2

Phase separation in the detergent Triton X-114 has been used as a physical characteristic to distinguish secreted proteins from amphipathic proteins. Since recombinant interleukin 2 is not secreted by bacteria, but is instead obtained from bacterial lysates, we have analysed several different recombinant interleukin 2 molecules as well as the naturally synthesized cytokine by phase separation in Triton X-114. Although naturally synthesized interleukin 2 and recombinant interleukin 2 from R&D Systems partitioned into the aqueous phase as expected for secreted molecules, recombinant interleukin 2 from Cetus separated into the detergent phase, indicating a high degree of amphipathicity. A recombinant AMGEN interleukin 2 mutated protein (mutein) exhibited intermediate behavior. Cetus and AMGEN interleukin 2 differ from the R&D Systems recombinant molecule and from the native lymphokine by a change in amino acid position 125. Spontaneous dimerization of the Cetus and AMGEN interleukin 2 muteins to a 31 kD form has also been observed whereas multimeric structures have not been found in the other interleukin 2 preparations. These distinct biochemical differences between the two recombinant molecules appear to be related to small changes in the primary structure, and they may be relevant to the therapeutic use of interleukin 2.