Isolation, Characterization, and Biological Significance of a Novel C-type Marine Lectin Purified from Scylla serrata Hemolymph.

Marine lectins are unique glycoproteins that induce non-specific immunity in fishes and crustaceans. Mud crab Scylla serrata (S. serrata) is of significant economic value and is widely distributed, though it is considered a prized species in Southeast Asian countries. However, the characterisation of the C-type specific lectins is still not explored properly. In this current study, a novel C-type lectin (Ss-Lec) was purified from the hemolymph of the mud crab S. serrata, revealing a 71 kDa protein with remarkable biochemical and functional diversity. The purified Ss-Lec displayed a single sharp X-ray diffraction (XRD ) peak at 31.7°, a distinct High-performance liquid chromatography (HPLC) retention time of 5.259 min, and characteristic Fourier Transform Infrared (FTIR) and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) profiles, confirming its high purity and structural integrity. Functionally, Ss-Lec exhibited strong hemagglutination activity at physiological pH (7-8) and moderate temperature (30 °C), with calcium dependence verified by EDTA (Ethylenediaminetetraacetic acid) inhibition. The lectin effectively agglutinated human erythrocytes and Saccharomyces cerevisiae, with activity specifically inhibited by N-acetylglucosamine, D-mannose, and fucose. Beyond its agglutination potential, Ss-Lec significantly enhanced cellular encapsulation and phenoloxidase activity, underscoring its immunomodulatory capacity. Notably, Ss-Lec demonstrated potent antibacterial activity against major aquatic pathogens, forming inhibition zones up to 7 mm, and exhibited robust antibiofilm effectsachieving 82% inhibition against Edwardsiella tarda and over 68% against other tested species. Collectively, these findings reveal Ss-Lec as a multifunctional immune lectin with promising antimicrobial and antibiofilm properties, highlighting its potential role in crustacean immunity and its future application as a natural bioactive molecule in aquaculture health management.