Identification, Cloning and Expression of Ferritin M-like Subunit from the Indian Oyster, Magallana bilineata...

Background/Objectives: Ferritins are key iron-sequestering proteins that maintain cellular homeostasis by storing iron in a bioavailable and nontoxic form. They also contribute to innate immunity, cellular proliferation and differentiation, shell formation, and protection against oxidative stress. In this study, we identified and characterized the M-type subunit of ferritin (Mbi-Fer) from the Indian backwater oyster, Magallana bilineata (Röding, 1798). Methods: A full-length cDNA of Mbi-Fer was sequenced and analyzed, and its gene expression was quantified in oysters collected from their natural habitat. Additionally, the coding region of Mbi-Fer was transformed and expressed in Escherichia coli, and the recombinant protein was purified and analyzed. Results: Mbi-Fer exhibited all the typical features of M-type ferritins, including the ferroxidation site of the H subunit and the nucleation core of the L subunit. The amino acid sequence alignment and phylogenetic analysis showed high similarity to the M-type ferritin subunits of Magallana gigas (Thunberg, 1793). A putative iron-responsive element was identified in the 5' UTR, indicating potential post-transcriptional regulation. Mbi-Fer expression in wild oysters was increased by more than fourfold, relative to laboratory-maintained control oysters. The recombinant expression result revealed a unique protein band that was specific to a ferritin M-like subunit, with an approximately molecular weight of 20 kDa. Conclusions: Our findings suggest that Mbi-Fer may play a role in both the iron storage and shell formation of backwater oysters and may serve as a valuable molecular marker of oxidative and environmental stress responses in estuarine bivalves.