Identification of the Allosteric Binding Site for Thiazolopyrimidine on the C-Type Lectin Langerin

Abstract

Langerin is a mammalian C-type lectin expressed on Langerhans cells in the skin. As an innate immune cell receptor, Langerin is involved in coordinating innate and adaptive immune responses against various incoming threats. We have previously reported a series of thiazolopyrimidines as murine Langerin ligands. Prompted by the observation that its human homologue exhibits different binding specificities for these small molecules, we report here our investigations to define their exact binding site. By using structural comparison and molecular dynamics simulations, we showed that the nonconserved short loops have a high degree of conformational flexibility between the human and murine homologues. Sequence analysis and mutational studies indicated that a pair of residues are essential for the recognition of the thiazolopyrimidines. Taking solvent paramagnetic relaxation enhancement NMR studies together with a series of peptides occupying the same site, we could define the cleft between the short and long loops as the allosteric binding site for these aromatic heterocycles.

Coarse-graining the recognition of a glycolipid by the C-type lectin Mincle receptor

“…Indeed, recent works have targeted a site near the long loop for the C-type lectin receptor Langerin. 70,71…”

Glycomimetics for the inhibition and modulation of lectins

“…38A and B ). 584 Whether the inhibition mechanism of the thiazolopyrimidines is based on the interference with the long loop, similar to what has been observed for E-selectin, covering the central fucose, remains to be elucidated. Interestingly, this cleft between the long and the short loop was previously reported to harbour a short peptide, suggesting it is amenable to modulation via small molecule inhibitors.…”

“… 161 In recent follow-up on this work, the binding site for this compound class was determined using NMR and computational methods. 584 The allosteric site of langerin is located in the cleft between the long and short loop, the so-called bridging region ( Fig. 38 ).…”

Secondary Sites of the C‐type Lectin‐Like Fold

“…Likewise, high‐throughput screenings (HTS) yielded biologically active and chemically tractable lead structures [89,129–131] . Follow‐up studies and mode of action analysis suggested some of these secondary sites to impact CLR function via unprecedented mechanisms, including allosteric modulation of the canonical CBS and changes in quaternary conformation [13,89,130–135] . For instance, a recently identified small molecule ligand was shown to inhibit LOX‐1‐dependent oxLDL uptake by cross‐linking two dimers in a head‐to‐head fashion, sterically blocking the basic spine region, and locking the receptor in an inactive tetramer state (Figure 3c, d and e).…”

“…[89,[129][130][131] Follow-up studies and mode of action analysis suggested some of these secondary sites to impact CLR function via unprecedented mechanisms, including allosteric modulation of the canonical CBS and changes in quaternary conformation. [13,89,[130][131][132][133][134][135] For instance, a recently identified small molecule ligand was shown to inhibit LOX-1-dependent oxLDL uptake by cross-linking two dimers in a head-to-head fashion, sterically blocking the basic spine region, and locking the receptor in an inactive tetramer state (Figure 3c, d and e). [89] Consequently, apart from their biological role, secondary sites have become increasingly relevant in the context of CTLtargeted drug discovery.…”