Bacteria binding and antibacterial activities of three small heat shock protein from the swimming crab, Portunus trituberculatus

Small heat shock proteins (sHSPs), a group of molecular chaperones with small molecular mass, are involved in immune responses in many organisms. However, the actual roles of sHSPs in immune defence against bacteria remain largely unclear. In this study, three sHSPs, named PtHSP10, PtHSP20 and PtHSP40 were identified from Portunus trituberculatus, and their immune function was investigated. Sequence analysis showed that the deduced amino acid sequences of PtHSP10, PtHSP20 and PtHSP40 exhibited conserved structures and the functional features. The tissue distributions and transcriptional profiles of these sHSPs in response to Vibrio alginolyticus challenge were analysed by quantitative real‐time PCR (qRT‐PCR). The results showed that the genes of the three sHSPs were ubiquitously expressed in various tissues, and mainly expressed in hepatopancreas or muscle. The transcriptions of these sHSPs in hepatopancreas of P. trituberculatus injected with V. alginolyticus were upregulated rapidly at 3 h post injection. Moreover, bacterial binding assay showed that the three sHSPs displayed distinct binding activities towards Gram‐negative bacteria (V. alginolyticus and V. parahaemolyticus) and Gram‐positive bacteria (Staphylococcus aureus). PtHSP10 could bind to V. parahaemolyticus and S. aureus, while PtHSP40 exhibited binding activity towards V. alginolyticus and V. parahaemolyticus. No binding was observed between PtHSP20 and the three tested bacteria. Moreover, PtHSP40 showed antibacterial activity against V. alginolyticus. Our findings indicated that these sHSPs displayed different immune function in immune defence.