Acid unfolding and self-association of recombinant Escherichia coli derived human interferon .gamma.

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Abstract
The secondary and tertiary structure of recombinant human interferon .gamma., determined by far and near-UV circular dichroism, showed a transition from the native state to an unfolded state below pH 4.5. The acid unfolding was extensively studied at pH 3.5 as a function of NaCl concentration. Addition of 0.05-0.2 M NaCl to a pH 3.5 sample sincreased the amount of .beta.-sheet structure with no change in the amount of .alpha.-helix and also induced reversible self-association of interferon .gamma. to form large aggregates from the monomer. When samples at pH 3.5 were dialyzed against 0.1 M ammonium acetate (pH 6.9) to refold interferon .gamma., the samples that contained NaCl in acid formed aggregates upon dialysis while those without NaCl formed a dimer apparently identical with the starting protein (i.e., before acid treatment). Thus, the self-association of interferon .gamma. in acid is closely correlated with its aggregation behavior in 0.1 M ammonium acetate after removal of acid.