Conservative and Atypical Ferritins of Sponges

Abstract

Ferritins comprise a conservative family of proteins found in all species and play an essential role in resistance to redox stress, immune response, and cell differentiation. Sponges (Porifera) are the oldest Metazoa that show unique plasticity and regenerative potential. Here, we characterize the ferritins of two cold-water sponges using proteomics, spectral microscopy, and bioinformatic analysis. The recently duplicated conservative <i>HdF1a/b</i> and atypical <i>HdF2</i> genes were found in the <i>Halisarca dujardini</i> genome. Multiple related transcripts of <i>HpF1</i> were identified in the <i>Halichondria panicea</i> transcriptome. Expression of <i>HdF1a/b</i> was much higher than that of <i>HdF2</i> in all annual seasons and regulated differently during the sponge dissociation/reaggregation. The presence of the MRE and HRE motifs in the <i>HdF1</i> and <i>HdF2</i> promotor regions and the IRE motif in mRNAs of <i>HdF1</i> and <i>HpF</i> indicates that sponge ferritins expression depends on the cellular iron and oxygen levels. The gel electrophoresis combined with specific staining and mass spectrometry confirmed the presence of ferric ions and ferritins in multi-subunit complexes. The 3D modeling predicts the iron-binding capacity of HdF1 and HpF1 at the ferroxidase center and the absence of iron-binding in atypical HdF2. Interestingly, atypical ferritins lacking iron-binding capacity were found in genomes of many invertebrate species. Their function deserves further research.