Abstract
Our bodies are continuously exposed to injurious insults by infection and tissue damage, which are primarily sensed by innate immune receptors to maintain homeostasis. Among such receptors is macrophage-inducible C-type lectin (Mincle, gene symbol CLEC4E), a member of the C-type lectin receptor (CLR) family, which functions as an immune sensor for both pathogens and damaged self. To monitor these injurious stimuli, Mincle recognizes disaccharide-based pathogen-derived glycolipids and monosaccharide-based intracellular metabolites, such as β-glucosylceramide. Mincle is well-conserved among mammals; however, there are questions that remain unclear, such as from which lower vertebrate did it arise and whether the original ligand was self or non-self. Here, we found homologues of Mincle and its signaling subunit Fc receptor γ chain (FcRγ) in lower vertebrates, such as reptiles, amphibians, and fishes. The crystal structure of a Mincle homologue revealed that fish Mincle possesses a narrower sugar-binding pocket than that of mammalian Mincle, and accommodates only monosaccharide moieties. These results suggest that Mincle may have evolved from a self-recognizing receptor, and its sugar-binding pocket widened during evolution, presumably to adapt to disaccharide-based glycolipids derived from life-threatening pathogens.