Bifunctional role of a pattern recognition molecule β-1,3 glucan binding protein purified from mangrove crab Episesarma tetragonum

• β-GBP was purified from the haemolymph of E. tetragonum and physicochemically characterized.
• Biological activity of E. tetragonum β-GBP substantiated by yeast agglutination and PO enhancing activity.
• Crystalline “Y” shaped β-GBP of E. tetragonum helped out solving the β-GBP structure.

β-1,3-Glucan binding protein (β-GBP) was purified from the haemolymph of Episesarma tetragonum by affinity chromatography with epoxy-activated laminarin-sepharose CL-6B column. E. tetragonum β-GBP exhibits a single band with a molecular weight of 100 kDa on SDS-PAGE and a pI of 5.9 in isoelectric focusing (IEF). The circular dichroism (CD) spectra result of E. tetragonum β-GBP indicates that the negative ellipticity bands near 220 nm and 208 nm correspond to the β-sheets in the secondary structure. Functional analysis results demonstrate that the purified E. tetragonum β-GBP agglutinates fungal cells (Candida albicans) containing β-glucan. This recognition and binding specificity leads to the activation of the prophenoloxidase (ProPO) cascade and enhance the phenoloxidase (PO) activity in a dose-dependent manner. Our finding discloses new insights in the ProPO activation and fungal agglutination of purified E. tetragonum β-GBP. It seems to play a significant role in microbial uncovering mechanism in invertebrates.

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