What makes the teeth of chitons iron hard?

A group of marine mollusks called chitons produce extraordinarily tough teeth, which they use to scrape algae off rocks for food. Now, researchers report the protein RTMP1 (radular teeth matrix protein 1) appears to guide the precise formation of the iron-based mineral magnetite in the ultra-hard teeth of chitons. The findings mark the first known instance of an iron oxide-forming protein in a eukaryote, offering new insights into biomineralization and potential inspiration for novel materials design. Throughout the animal kingdom, many organisms form hard body parts, like teeth, bones, and shells, through a process called biomineralization. Among these, chitons produce extraordinarily tough teeth. Chiton teeth form within the radular sac on a conveyor belt-like structure, where specialized cells lay down organic templates that undergo staged mineralization, culminating in new, hard magnetite teeth. However, the underlying mechanism that governs the mineralization of iron in chiton teeth remains largely a mystery. Previous research has identified several proteins thought to be associated with this process. Of these, RTMP1 was identified as a strong contender in orchestrating the mineralization of magnetite in chiton teeth.

By analyzing gene expression across various chiton species, Michiko Nemoto and colleagues found that RTMP1 is evolutionarily conserved, implying a function unique to chitons. Using immunolabeling techniques, the authors detected RTMP1 not only within the teeth but also in the epithelial cells surrounding tooth cusps undergoing mineralization. Notably, the localization of RTMP1 shifted in correlation with the stages of mineral deposition – initially dispersed symmetrically, then concentrating on the nonmineralized side of the tooth after iron oxide began to accumulate. Within the cusps, RTMP1 formed narrow bands that migrated from the leading to the trailing edge as mineralization progressed. According to Nemoto et al., these dynamic, spatially controlled patterns strongly suggest that RTMP1 plays a pivotal, regulated role in directing iron oxide mineralization in chiton teeth. “Molecular details of biomineralization processes could provide the ability to mimic nature’s mineralization strategies for the synthesis of new materials,” writes André Sheffel in a related study.