Crystal structure of the macrophage migration inhibitory factor from rat liver

Abstract
The tertiary structure of the macrophage migration inhibitory factor (MIF) from rat liver (12,300 Mr) is presented at 2.2 Å resolution. Each monomer consists of two β/α/β motifs aligned in quasi two-fold symmetry, comprising a domain consisting of a four-stranded mixed β-sheet and two antiparallel α-helices. The protein exists as a trimer in the crystal. An extra β-strand that is almost perpendicular to the other β-strands joins to the β-sheet of the neighbouring monomer in the trimer. Unexpected similarities were detected between MIF and two kinds of isomerase.