Antigen uptake and processing by innate immune cells is crucial to initiate the immune response. Therein, the endocytic C-type lectin receptors recognize pathogens by their glycan structures enabling decision-making in innate immunity. Herein, we studied the carbohydrate recognition domain of Langerin, a C-type lectin receptor involved in the host defense against viruses such as HIV and influenza as well as bacteria and fungi. Using a combination of nuclear magnetic resonance and molecular dynamics simulations, we unraveled the molecular determinants underlying cargo capture and release encoded in the receptor architecture. Our findings revealed receptor dynamics over several timescale associated with binding and release of the essential cofactor Ca2+ controlled by the coupled motions of two loops. Moreover, mutual information theory and site-directed mutagenesis exposed an allosteric intra-domain network that modulates the Ca2+ affinity depending on the pH thereby promoting fast ligand release.
An intra-domain allosteric network modulates the calcium affinity of the C-type lectin receptor Langerin.