Structure activity studies of the cytokine macrophage migration inhibitory factor (MIF) reveal a critical role for its carboxy terminus.

Carboxy-truncated mutants of human MIF (MIF(1-104) and MIF(1-109)) were used in structure activity studies. CD spectroscopy revealed an overall structural similarity between the mutants and MIF. Denaturant-induced unfolding demonstrated that the C-terminus contributed significantly to the conformational stability of MIF. This appears to be due to the formation of two C-terminal beta-strands. The mutants were enzymatically active, exhibiting half of the enzymatic redox activity of MIF. However, immunological analysis showed that deletion of both 5 and 10 C-terminal residues resulted in loss of the macrophage activating properties of MIF, providing functional evidence that the C-terminus is important for immunological activity and trimer formation. A more detailed study of the C-terminus may assist in identifying the molecular basis for the immunological and enzymatic activities of MIF.