Identification and function analysis of a scavenger receptor B gene in red swamp crayfish Procambarus clarkii

Scavenger receptor (SRs) are pattern recognition receptors that play important roles in innate immunity. However, studies on SR in Procambarus clarkii are still lacking. In the present study, a novel scavenger receptor B on P. clarkii (PcSRB) was identified. The ORF of PcSRB was 548 bp and encoded 505 amino acid residues. It was a transmembrane protein with two transmembrane domains. The molecular weight was about 57.1 kDa. The tissue analysis by real-time PCR showed that the highest expression level was found in hepatopancreas, while the lowest expression level was found in heart, muscle, nerve and gill. After P. clarkii were infected with Aeromonas hydrophila, the expression of SRB in hemocytes increased rapidly at 12 h, and SRB in hepatopancreas and intestine also increased rapidly at 48 h after infection. The recombinant protein was obtained by prokaryotic expression. The recombinant protein (rPcSRB) could bind to bacteria and different molecular pattern recognition substances. The present study confirmed that SRB may be involved in the immune regulation process and play a certain role in the immune defense of P. clarkii, especially in the recognition and binding of pathogens. Therefore, this study provides theoretical support for further improving and enriching the immune system of P. clarkii.