Structure and interactions of the phloem lectin (phloem protein 2) Cus17 from Cucumis sativus

Phloem protein 2 (PP2) contributes crucially to phloem-based defense in plants by binding to carbohydrates displayed by pathogens. However, its three-dimensional structure and the sugar binding site remained unexplored. Here, we report the crystal structure of the dimeric PP2 Cus17 from Cucumis sativus in its apo form and complexed with nitrobenzene, N-acetyllactosamine, and chitotriose. Each protomer of Cus17 consists of two antiparallel four-stranded twisted β sheets, a β hairpin, and three short helices forming a β sandwich architectural fold. This structural fold has not been previously observed in other plant lectin families. Structure analysis of the lectin-carbohydrate complexes reveals an extended carbohydrate binding site in Cus17, composed mostly of aromatic amino acids. Our studies suggest a highly conserved tertiary structure and a versatile binding site capable of recognizing motifs common to diverse glycans on plant pathogens/pests, which makes the PP2 family suited for phloem-based plant defense. [Display omitted] •The structure of dimeric Cus17, a phloem protein 2 superfamily member, is reported•The structure reveals a yet unobserved plant lectin fold with a β sandwich architecture•Cus17 binds chito-oligosaccharides and N-linked mannosyl and complex glycans Phloem protein 2 (PP2) are important for phloem-based plant defense. Bobbili et al. characterize the glycan binding properties of the Cucurbitaceae family PP2 member Cus17, and they report the crystal structures of Cus17 alone and its sugar-bound complexes.