Structural Studies of Langerin and Birbeck Granule: A Macromolecular Organization Model

Abstract

Dendritic cells, a sentinel immunity cell lineage, include different cell subsets that express various C-type lectins. For example, epidermal Langerhans cells express langerin, and some dermal dendritic cells express DC-SIGN. Langerin is a crucial component of Birbeck granules, the Langerhans cell hallmark organelle, and may have a preventive role toward HIV, by its internalization into Birbeck granules. Since langerin carbohydrate recognition domain (CRD) is crucial for HIV interaction and Birbeck granule formation, we produced the CRD of human langerin and solved its structure at 1.5 A resolution. On this basis gp120 high-mannose oligosaccharide binding has been evaluated by molecular modeling. Hydrodynamic studies reveal a very elongated shape of recombinant langerin extracellular domain (ECD). A molecular model of the langerin ECD, integrating the CRD structure, has been generated and validated by comparison with hydrodynamic parameters. In parallel, Langerhans cells were isolated from human skin. From their analysis by electron microscopy and the langerin ECD model, an ultrastructural organization is proposed for Birbeck granules. To delineate the role of the different langerin domains in Birbeck granule formation, we generated truncated and mutated langerin constructs. After transfection into a fibroblastic cell line, we highlighted, in accordance with our model, the role of the CRD in the membrane zipping occurring in BG formation as well as some contribution of the cytoplasmic domain. Finally, we have shown that langerin ECD triggering with a specific mAb promotes global rearrangements of LC morphology. Our results open the way to the definition of a new membrane deformation mechanism.

DC-SIGN Neck Domain Is a pH-sensor Controlling Oligomerization

“…Oligomeric ECD tightly bound to the mannan-agarose column through an avidity based mechanism. Monomeric CRD, in contrast, with a low affinity for its natural ligands, did not firmly bind to the mannan-agarose column and was only delayed as previously described for other C-type lectin CRDs (48,49). However, following a prior concentration to minimize the sample volume, monomeric CRD could be separated from the flowthrough on the mannan-agarose column.…”

Inhibition of Two Temporal Phases of HIV-1 Transfer from Primary Langerhans Cells to T Cells: The Role of Langerin

“…We showed that langerin can be expressed as a homotrimer, similar to that of the soluble extracellular domain ECD (53) and that this enhances its ability to bind HIV, with no evidence of covalent langerin binding to CD4 or CCR5. These studies guided the choice of soluble langerin homologs to test as inhibitors of HIV binding to eLCs, including the trimeric ECD and the key-binding domain, the CRD.…”

Human blood BDCA-1 dendritic cells differentiate into Langerhans-like cells with thymic stromal lymphopoietin and TGF-β

“…The mean width of the Birbeck granules was 33 nm, which corresponds to what has been observed on freshly isolated human LCs. 29 The CD1a and CD207 singlepositive, as well as double-negative, cells were consistently negative for Birbeck granules (data not shown).…”