Characterization of the macrophage migration inhibitory factor-binding site of sarcolectin and its relationship to human serum albumin.

The sialic acid-binding protein sarcolectin from human placenta specifically interacts with the lymphokine macrophage migration inhibitory factor, enabling its convenient purification and histochemical localization. After cyanogen bromide-mediated cleavage of sarcolectin one polypeptide with an apparent molecular weight of approximately 15,000 exhibited binding capacity to the labelled lymphokine, as revealed by ligand blotting. The N-terminal sequence stretch of this peptide is identical to the respective sequence of human serum albumin, following the internal methionine residue in position 298. Cleavage at a methionine moiety in position 446 can explain the size of the 15 KDa product of chemical degradation. Close similarity of circular dichroism of sarcolectin and human serum albumin added further evidence to their structural similarity, calling for further studies to rigorously define their relationship.