[4S04a] 19. Marine Biotechology - Part 2

3:00 PM - 3:20 PM JST(6:00 AM - 6:20 AM UTC)

[4Marine-08-KL] Identification and Functional Characterization of RTMP1, a Chiton-Specific Protein Involved in Iron Oxide Biomineralization

○Michiko Nemoto¹, Koki Okada², Haruka Akamine¹, Yuki Odagaki¹, Yuka Narahara¹, Kenji Okoshi³, Kiori Obuse¹, David Kisailus⁴, Hisao Moriya¹, Akira Satoh¹ (1. Okayama University (Japan), 2. JFE Techno-Research Corporation (Japan), 3. Toho University (Japan), 4. University of California at Irvine (USA))

Keywords:

Biomineralization,iron oxide,chiton

Living organisms form hard tissues such as bones and teeth by concentrating inorganic ions and inducing mineralization. While the formation of hard tissues utilizing calcium (Ca) and silicon (Si)—including their regulatory proteins—has been extensively studied, the molecular mechanisms underlying the formation of iron (Fe)-based hard tissues have remained largely unexplored. We have focused our research on chitons, a group of mollusks that concentrate iron to form magnetite (Fe₃O₄) in their teeth. Chitons deposit magnetite at the tooth cusps of the radula, a feeding apparatus. Through a proteomic analysis of the tooth cusps of the chiton Cryptochiton stelleri, we previously identified 22 cusp-specific proteins. Among them was a novel protein with no detectable homology to any known proteins, which we designated as Radular Teeth Matrix Protein 1 (RTMP1). In our recent comparative transcriptome analysis of the radular tissues from three additional chiton species, homologs of RTMP1 were also found to be conserved among these species. Furthermore, immunofluorescence localization analysis revealed that RTMP1 is highly expressed in epithelial cells surrounding the teeth prior to iron deposition and is prelocalized within the future iron-deposition region inside the teeth. In vitro functional assays further demonstrated that iron oxides are formed in the presence of recombinant RTMP1 fragments. Taken together, these results suggest that RTMP1, a protein conserved among chitons, plays a crucial role in the deposition of iron oxides within their teeth.