Conserved dimerization architecture in C-type lectins from virus-vector mosquitoes

C-type lectins (CTLs) play key roles in immunity and microbial carbohydrate recognition. In the vector-mosquito Aedes aegypti, the C-type lectin domain-single (CTLD-S) family comprises 34 soluble CTLs whose members are implicated in flavivirus dissemination and microbial homeostasis, yet their organization remains uncharacterized. We combine X-ray crystallography, small-angle X-ray scattering (SAXS), molecular dynamics, and machine learning-based structure prediction to characterize CTLs in Aedes aegypti. We determined the crystal structures of four representative CTLD-S proteins: mosGCTL-1, -3, -6, and -20. All crystals featured an identical homodimer arrangement, positioning both carbohydrate-binding sites on the same molecular face. Dimerization was confirmed in solution and AlphaFold predictions across the entire family indicated that dimer formation may be a unifying feature of CTLD-S proteins. For one mosGCTL structure, paucimannose glycans bound at a Ca²⁺-dependent site, demonstrating bidentate binding through one dimer. Machine learning-based predictions indicated hundreds of possible CTLD-S heterodimers may be viable, with wide-ranging implications for preferred glycan binding through one dimer. Our findings reveal a conserved dimeric arrangement among mosquito lectins that may underpin ligand recognition relevant to vector-pathogen interactions.