IDENTIFICATION AND EXPRESSION OF HEAT SHOCK PROTEIN 60 (HSP60) FROM THE ARK SHELL SCAPHARCA BROUGHTONH

Heat shock protein 60 (HSP60) is evolutionarily highly conserved, and it assists with protein folding in the mitochondria and serves as a molecular chaperone, increasing cell survival under various conditions. Studies of HSP60 in molluscs under stress conditions remain limited. Here, this study first characterize a full-length HSP60 cDNA from the ark shell Scapharca broughtonii (termed SbHSP60) containing a 1,725-bp open reading frame corresponding to a deduced protein of 574 amino acid residues with a predicted molecular mass of approximately 61.4 kDa. The deduced protein has 72.3%-80.3% amino acid identity with homologs from invertebrates and vertebrates. Phylogenetic analysis showed that SbHSP60 grouped with proteins from other molluscs, forming a sister cluster to the HSP60 proteins from vertebrates. The expression pattern of SbHSP60 as examined by quantitative real-time PCR suggested that these mRNA transcripts were distributed across all examined tissues. The highest levels of expression were found in the hepatopancreas and gill, with decreasing levels of expression in the mantle, foot, hemocytes, and adductor muscle. Expression of SbHSP60 after challenge with Vibrio anguillarum showed similar upregulation profiles in the hepatopancreas and gill, indicating that SbHSP60 is involved in the bacterial defense process as an acute-phase protein. Levels of SbHSP60 in the hepatopancreas and gill were higher in cadmium-exposed individuals than in controls. SbHSP60 was significantly upregulated by Cd stress in the gill, but expression was less affected in the hepatopancreas, implying different roles in cellular Cd stress protection. The effects of heat stress on SbHSP60 mRNA expression were duration- and tissue-specific. The induction of SbHSP60 in the heat-stressed group occurred predominantly in the hepatopancreas, suggesting that protein damage and the consequent requirement for the HSP60 protein are increased during the heat shock process.