Phenoloxidase activation, antimicrobial, and antibiofilm properties of β-glucan binding protein from Scylla serrata crab hemolymph

In this study, we purified β-GBP from hemolymph of Scylla serrata crabs using affinity chromatography. The purified S. serrata β-GBP (Ss-β-GBP) had 100 kDa molecular mass in the SDS-PAGE. MALDI-TOF/TOF analysis was conducted, revealing that the purified 100 kDa protein had 96% similarity with β-GBP of Astacus leptodactylus. Ss-β-GBP was characterized using high-performance liquid chromatography (HPLC), X-ray diffraction (XRD) analysis, circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy, which confirmed the structure of the Ss-β-GBP. The purified Ss-β-GBP was functionally analyzed by yeast agglutination and phagocytic reaction assays. Moreover, the PO enhancing ability of Ss-β-GBP was evidenced through PO activity. Specifically, the antibacterial activity of the Ss-β-GBP against Gram-positive (Enterococcus faecalis and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria was evaluated by determining its minimum inhibitory concentration (MIC) < 60 μg/ml for all tested species. Furthermore, the antibiofilm efficacy of Ss-β-GBP at 50 and 100 μg/ml was outlined using light microscopy and confocal laser scanning microscopy (CLSM). Bacterial viability assays also outlined the dose-dependent activity of Ss-β-GBP based on the ratio of live/dead bacterial cells. The results of this study revealed that crab-borne Ss-β-GBP might be widely used to suppress the growth of pathogenic bacteria.