Characterization and comparison of two C-type lectins with novel key motifs from mud crab Scylla paramamosain.

As an important pattern recognition receptor (PRR) in the innate immune system, C-type lectin plays an important role in the innate immune process of invertebrates. Two C-type lectins SpCTL-C and SpCTL-D were characterized from mud crab (Scylla paramamosain). The predicted SpCTL-C and SpCTL-D proteins both contain a single carbohydrate-recognition domain (CRD) with key motif Gln-Pro-Ala (QPA) and Met-Pro-Ala (MPA), respectively. SpCTL-C and SpCTL-D transcripts distributed in all examined tissues, and the expression level was the highest in hepatopancreas. As PRR, the purified recombinant proteins rSpCTL-C and rSpCTL-D have high affinity for three kinds of pathogen-associated molecular patterns (PAMPs): β-glucan, lipopolysaccharide, and peptidoglycan. Besides, rSpCTL-D can bind to all nine microorganisms tested, while rSpCTL-C can bind to seven microorganisms except for Staphylococcus aureus and Micrococcus luteus. Both rSpCTL-C and rSpCTL-D showed agglutination activity towards fungi Pichia pastoris and Saccharomyces cerevisiae. However, rSpCTL-C and rSpCTL-D exhibited different antimicrobial activities: rSpCTL-D has a certain inhibitory effect on the growth of Vibrio fluvialis and M. luteus, while rSpCTL-C has no obvious inhibitory activity. The results show that rSpCTL-C and rSpCTL-D had better phagocytosis-promoting effect on M. luteus than the negative control. Meanwhile, both rSpCTL-C and rSpCTL-D had certain encapsulation-promoting activity. Collectively, two C-type lectins with novel key motifs make an important impact as PRR in immune response towards pathogens. At the same time, they play different functions in the innate immunity of mud crab S. paramamosain. [ABSTRACT FROM AUTHOR]