A novel C1q domain-containing protein isolated from the bivalve mollusk Modiolus kurilensis recognizing glycans enriched with acidic galactans

C1q domain-containing (C1qDC) proteins are a group of biopolymers involved in immune response as pattern recognition receptors (PRRs) in a lectin manner identifying and binding carbohydrate components of pathogen-associated molecular patterns (PAMPs). In the current study, we present a new protein MkC1qDC-1 purified from the hemolymph plasma of Modiolus kurilensis bivalve mollusk widespread in the Northwest Pacific. The isolation procedure included ammonium sulfate precipitation followed by affinity chromatography on pectin-Sepharose. The full-length MkC1qDC-1 sequence was assembled based on mass-spectrometry data supplemented with N-terminal Edman sequencing, and included 156 amino acid residues displaying high homology to C1qDC proteins of bivalves. 2-D electrophoresis of purified MkC1qDC-1 showed a single polypeptide with 19 kDa mass and pI 5.2 in accordance with predicted values. The protein was functionally active after 1 h incubation in temperatures up to 50°C and stable over a wide pH range. MkC1qDC-1 demonstrated antibacterial properties against gram-negative and gram-positive strains.