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

C-type lectins (CTLs) play key roles in innate immunity and microbial carbohydrate recognition. In the disease vector mosquito Aedes aegypti, the CTLD-S family comprises 34 soluble CTLs whose members are implicated in flavivirus dissemination and microbial homeostasis, yet their structure and organization remain uncharacterized. Here, 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 mosGCTL proteins in 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 CTLD-S family indicated that dimer formation may be a unifying feature of mosquito CTLD-S proteins. For one mosGCTL structure, paucimannose glycans bound at a Ca2+-dependent site, demonstrating bi-dentate glycan-binding through one dimer. Finally, 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 carbohydrate recognition relevant to vector-pathogen interactions.