Characterization of Multisugar-Binding C-Type Lectin (<em>Spli</em>Lec) from a Bacterial-Challenged Cotton Leafworm, <em>Spodoptera littoralis</em>

<div><h3>Background</h3><p>Various proteins that display carbohydrate-binding activity in a Ca²⁺-dependent manner are classified into the C-type lectin family. They have one or two C-type carbohydrate-recognition domains (CRDs) composed of 110–130 amino acid residues in common. C-type lectins mediate cell adhesion, non-self recognition, and immuno-protection processes in immune responses and thus play significant roles in clearance of invaders, either as cell surface receptors for microbial carbohydrates or as soluble proteins existing in tissue fluids. The lectin of <em>Spodoptera littoralis</em> is still uncharacterized.</p> <h3>Methodology</h3><p>A single <em>orf</em> encoding a deduced polypeptide consisting of an 18-residue signal peptide and a 291-residue mature peptide, termed <em>Spli</em>Lec, was isolated from the haemolymph of the cotton leafworm, <em>S. littoralis</em>, after bacterial challenge using RACE-PCR. Sequence analyses of the data revealed that <em>Spli</em>Lec consists of two CRDs. Short-form CRD₁ and long-form CRD₂ are stabilized by two and three highly conserved disulfide bonds, respectively. <em>Spli</em>Lec shares homology with some dipteran lectins suggesting possible common ancestor. The purified <em>Spli</em>Lec exhibited a 140-kDa molecular mass with a subunit molecular mass of 35 kDa. The hemagglutination assays of the <em>Spli</em>Lec confirmed a thermally stable, multisugar-binding C-type lectin that binds different erythrocytes. The purified <em>Spli</em>Lec agglutinated microorganisms and exhibited comparable antimicrobial activity against gram (+) and gram (−) bacteria too.</p> <h3>Conclusions</h3><p>Our results suggested an important role of the <em>Spli</em>Lec gene in cell adhesion and non-self recognition. It may cooperate with other AMPs in clearance of invaders of <em>Spodoptera littoralis</em>.</p>