Sialic acid-specific lectin participates in an immune response and ovarian development of the banana shrimp Fenneropenaeus merguiensis.

A sialic acid-specific lectin was purified from the hemolymph of Fenneropenaeus merguiensis by repetitive affinity fetuin-agarose column chromatography. The purified F. merguiensis lectin (called FmL) consisted of two distinct 30.9 and 32kDa subunits with identical N-terminal amino acid sequences of ten residues. FmL was also composed of sugar moieties; glucosamine, glucose, mannose and N-acetyl neuraminic acid but not N-glycolyl neuraminic acid. It was postulated to be a glycoprotein as it was positively stained by glycoprotein staining kit and detected by some bionylated plant lectins. Deglycosylation by either peptide N-glycosidase F or trifluoromethanesulfonic acid turned both types of FmL subunits to 28kDa peptides. The internal peptide sequence of FmL was similar to a fibrinogen-related domain of human ficolin and the horseshoe crab lectin. Determination of the lectin concentrations in the hemolymph was performed by ELISA while its hemaglutinating activity (HA) was tested by hemagglutination. Both specific lectin concentrations and HA increased as shrimp developed ovarian maturation stages 2 to 4. Their constitutive levels were found in pre-vitellogenic females and higher than those of males. Both specific lectin concentrations and HA of FmL were inducible to the highest levels at 12h after F. merguiensis was challenged by pathogenic Vibrio harveyi. The FmL-induced agglutination of V. harveyi was specifically abolished by sialic acid, fetuin and bacterial cell wall components. These findings might indicate the implication in an immune response of FmL to protect the shrimp themselves or their spawning eggs towards pathogenic bacteria in surrounding environment.