The lectin self of complement factor H.

Complement, a part of the humoral innate immune system, is divided into three pathways. The classical and mannose-binding lectin pathways are triggered by specific recognition of foreign targets. Conversely, the alternative pathway (AP) is actively down-regulated on host tissue.

Complement Factor H and Simian Virus 40 bind the GM1 ganglioside in distinct conformations.

Mammalian cell surfaces are decorated with a variety of glycan chains that orchestrate development and defense and are exploited by pathogens for cellular attachment and entry. While glycosidic linkages are, in principle, flexible, the conformational space that a given glycan can sample is subject to spatial and electrostatic restrictions imposed by its overall chemical structure. Here, we show how the glycan moiety of the GM1 ganglioside, a branched, monosialylated pentasaccharide that serves as a ligand for various proteins, undergoes differential conformational selection in its interactions with different lectins.