Big defensin 2

We report here the first evidence in an invertebrate, the oyster Crassostrea gigas, of a phenomenon of Presence-Absence Variation (PAV) affecting immune-related genes. We previously evidenced an extraordinary interindividual variability in the basal mRNA abundances of oyster immune genes including those coding for a family of antimicrobial peptides, the big defensins (Cg-BigDef). Cg-BigDef is a diverse family composed of three members: Cg-BigDef1 to -3. Here, we show that besides a high polymorphism in Cg-BigDef mRNA expression, not all individual oysters express simultaneously the three Cg-BigDefs. Moreover, in numerous individuals, no expression of Cg-BigDefs could be detected. Further investigation at the genomic level revealed that in individuals in which the transcription of one or all Cg-BigDefs was absent the corresponding Cg-bigdef gene was missing. In our experiments, no correlation was found between Cg-bigdef PAV and oyster capacity to survive Vibrio infections. The discovery of P-A immune genes in oysters leads to reconsider the role that the immune system plays in the individual adaptation to survive environmental, biotic and abiotic stresses.

Tachylectin-5, a 41-kDa protein with a common fold of the C-terminal globular domain of the γ-chain of fibrinogen, is purified from horseshoe crab hemolymph plasma by affinity column chromatography, using acetyl-group-immobilized resin. Two types of isolectins, tachylectin-5A and tachylectin-5B, are obtained by stepwise elution with GlcNAc at 25 and 250 mM, respectively. Tachylectins-5A and -5B exhibit extraordinarily strong hemagglutinating activity against all types of human erythrocytes (the minimum agglutinating concentration of 0.004-0.008 μg/mL for tachylectin-5A and 0.077-0.27 μg/mL for tachylectin-5B). Their hemagglutinating activities are inhibited by acetyl group-containing sugars and noncarbohydrates such as sodium acetate, acetylcholine, and acetyl CoA (the minimum inhibitory concentrations of 1.3-1.6 mM), indicating that the acetyl group is required and sufficient for recognition by tachylectins-5A and -5B. EDTA inhibits their hemagglutinating activity, whereas the inhibition is overcome by adding an excess amount of Ca2+. Tachylectins-5A and -5B also exhibit bacterial agglutinating activity against both Gram-negative bacteria (the minimum agglutinating concentrations of 0.04-0.08 μg/mL for tachylectin-5A and 0.05-0.11 μg/mL for tachylectin-5B) and Gram-positive bacteria (the minimum agglutinating concentrations of 0.3-2.4 μg/mL for tachylectin-5A and 15.1-26.8 μg/mL for tachylectin-5B). Interestingly, tachylectins-5A and -5B enhance the antimicrobial activity of a hemocyte-derived peptide, big defensin.