Lectin of the Bivalve Glycymeris yessoensis as a Pattern Recognition Receptor

C-type lectins are a superfamily of Ca 2+ -dependent carbohydrate-recognizing proteins that often serve as pattern recognition receptors (PRRs), which bind with specific molecular patterns known as pathogen-associated molecular patterns (PAMPs) of certain microorganisms. A new C-type lectin specific for highly branched mannans (GYLman) was isolated from the hemolymph of the mollusk Glycymeris yessoensis. GYLman was an oligomer with a molecular mass of more than 250 kDa by SDS-PAGE and showed a single band of approximately 70 kDa in reducing conditions. Lectin hemagglutination activity was best inhibited by highly branched yeast mannan with α-1,6-linked mannopyranose backbone and α-1,2-linked mannopyranose side chains. The mannan structure was established using 1 H and 13 C NMR spectroscopy. GYLman activity was reversibly inhibited by EDTA, was maximal in a pH range of 7–9, and was completely abolished by heating at 90°C. Acting as a PRR, GYLman specifically interacted with various PAMPs, including Escherichia coli lipopolysaccharide (LPS) O111:B4, α-D-mannan, β-1,3-glucan, and peptidoglycan, and bound to both Gram-positive ( Staphylococcus aureus and Bacillus subtilis ) and Gram-negative ( E. coli and Vibrio proteolyticus ) bacteria and the yeast Candida albicans , suggesting a broad PAMP recognition spectrum.