A rhamnose-binding lectin from sea bass (Dicentrarchus labrax) plasma agglutinates and opsonizes pathogenic bacteria.
The discovery of rhamnose-binding lectins (RBLs) in teleost fish eggs led to the identification of a novel lectin family characterized by a unique sequence motif and a structural fold, and initially proposed to modulate fertilization. Further studies of the RBL tissue localization and gene organization were also suggestive of role(s) in innate immunity. Here we describe the purification, and biochemical and functional characterization of a novel RBL (DlRBL) from sea bass (Dicentrarchus labrax) serum. The purified DlRBL had electrophoretic mobilities corresponding to 24 kDa and 100 kDa under reducing and non-reducing conditions, respectively, suggesting that in plasma the DlRBL is present as a physiological homotetramer. DlRBL subunit transcripts revealed an open reading frame encoding 212 amino acid residues that included two tandemly-arrayed carbohydrate-recognition domains, and an 18-residue signal sequence at the N-terminus. The deduced size of 24.1 kDa for the mature protein was in good agreement with the subunit size of the isolated lectin. Binding activity of DlRBL for rabbit erythrocytes could be inhibited in the presence of rhamnose or galactose, did not require calcium, and was optimal at around 20°C and within the pH 6.5-8.0 range. DlRBL agglutinated Gram positive and Gram negative bacteria, and exposure of formalin-killed Escherichia coli to DlRBL enhanced their phagocytosis by D. labrax peritoneal macrophages relative to the unexposed controls. Taken together, the results suggest that plasma DlRBL may play a role in immune recognition of microbial pathogens and facilitate their clearance by phagocytosis.
Department of Biological, Chemical, Pharmaceutical Science and Technology, Marine Immunobiology Laboratory, University of Palermo, Via Archirafi 18, Palermo, Italy. Electronic address: matteo.cammarata@unipa.it.
Matteo
M
Cammarata
Department of Biological, Chemical, Pharmaceutical Science and Technology, Marine Immunobiology Laboratory, University of Palermo, Via Archirafi 18, Palermo, Italy.
Maria Giovanna
MG
Parisi
Department of Biological, Chemical, Pharmaceutical Science and Technology, Marine Immunobiology Laboratory, University of Palermo, Via Archirafi 18, Palermo, Italy.
Gigliola
G
Benenati
Department of Microbiology and Immunology, University of Maryland School of Medicine, UMB, IMET, Suite 236, Columbus Center, 701 East Pratt Street, Baltimore, MD 21202, USA.
Gerardo R
GR
Vasta
Department of Biological, Chemical, Pharmaceutical Science and Technology, Marine Immunobiology Laboratory, University of Palermo, Via Archirafi 18, Palermo, Italy.
Nicolò
N
Parrinello
D000371:Agglutination; D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001424:Bacterial Infections / Q000276:immunology*; D001492:Bass / Q000276:immunology*; D004912:Erythrocytes / Q000378:metabolism*; D004926:Escherichia coli / Q000276:immunology*; D007113:Immunity, Innate; D037102:Lectins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000276:immunology*; D008969:Molecular Sequence Data; D010587:Phagocytosis; D010802:Phylogeny; D010949:Plasma / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary / Q000235:genetics; D011817:Rabbits; D012210:Rhamnose / Q000378:metabolism
D037102:Lectins; D012210:Rhamnose
Bacteria; Dicentrarchus labrax; Hemagglutinins; Opsonin; Rhamnose binding lectin; Teleost