In Vitro Study of Magnesium‐Calcite Biomineralization in the Skeletal Materials of the Seastar Pisaster giganteus

Abstract

The mechanisms of formation of biogenic magnesium-rich calcite remain an enigma. Here we present ultrastructural and compositional details of ossicles from the seastar Pisaster giganteus (Echinodermata, Asteroidea). Powder X-ray diffraction, infrared spectroscopy and elemental analyses confirm that the ossicles are composed of magnesium-rich calcite, whilst also containing about 0.01 % (w/w) of soluble organic matrix (SOM) as an intracrystalline component. Amino acid analysis and N-terminal sequencing revealed that this mixture of intracrystalline macromolecules consists predominantly of glycine-rich polypeptides. In vitro calcium carbonate precipitation experiments indicate that the SOM accelerates the conversion of amorphous calcium carbonate (ACC) into its final crystalline product. From this observation and from the discovery of ACC in other closely related taxa, it is suggested that substitution of magnesium into the calcite lattice through a transient precursor phase may be a universal phenomenon prevalent across the phylum echinodermata.

Revisiting geochemical controls on patterns of carbonate deposition through the lens of multiple pathways to mineralization

“…Here, ACC is the initial precipitate and it subsequently transforms to HMg calcite with Mg contents up to 20 mol% MgCO 3 . This composition range is reported for the skeletal structures of diverse calcifying organisms 17,22,[48][49][50] and also seen in some sedimentary environments.…”

A crayfish molar tooth protein with putative mineralized exoskeletal chitinous matrix c properties

“…Moreover, several crustacean proteins associated with calcification processes present amino acid composition profiles similar to that of Cq-M15 (Inoue et al, 2004;Glazer et al, 2010). In fact, such shared patterns of amino acid composition were also found in proteins from organic matrices involved in invertebrate calcium carbonate precipitation (Faircloth and Shafer, 2007;Gayathri et al, 2007;Marie et al, 2007;Inoue et al, 2008;Suzuki et al, 2013), as well as in protein extracted from vertebrate enamel (Robinson et al, 2005).…”

“…Cq-M15 has low percentages of acidic and putatively phosphorylated amino acids and possesses an RR1-type chitinbinding motif, which are more compatible with the properties of structural cuticular proteins (Willis, 2010) and, as such, do not favor an interaction with ions. However, Cq-M15 could be acidic enough to interact in mineral precipitation as has been discovered with other hydrophilic and acidic molecules involved in the regulation of crystal nucleation and growth during biological mineralization in vertebrates (He et al, 2005;Gayathri et al, 2007), as well as in invertebrates Luquet, 2012). Moreover, several crustacean proteins associated with calcification processes present amino acid composition profiles similar to that of Cq-M15 (Inoue et al, 2004;Glazer et al, 2010).…”

Aragonite coating solutions (ACS) based on artificial seawater

“…The incorporation of Mg 2+ ion of smaller radius (86 pm), in comparison to larger Ca 2+ (114 pm), into the calcite lattice also shows itself in slightly reduced lattice parameters for the magnesian-calcite. Magnesian-calcite is the phase of micro-porous skeletons of sea stars (i.e., starfish) [70].…”