Evolutionary requirements for controlled biomineralization
Biomineralization is the process by which living organisms produce minerals. The ability to form genetically determined mineralized skeletons must have existed for the past 550 million years. However, key molecular and evolutionary mechanisms which led to this ability are still far from being understood [1].
Especially, understanding enzymatic and biosynthetic aspects of chitin mineralization is still in its infancy. The chitin synthases of molluscs differ from chitin synthases of all other organisms mainly in two aspects: A myosin domain [2], and highly conserved, mollusc-specific patterns of charged amino acids [3]. The latter bear the potential to interact in a pH-dependent manner, either with themselves, or with mineral phases and/or with highly charged biomineralization proteins. The molecular diversity of these so-called "biomineralization proteins" is enormous, perhaps one of the reasons for deflecting attention away from mollusc chitin synthases until today [4].
Current technical and conceptual frontiers in this research area are related to
(a) the lack of understanding species-specific biomechanical circuits at the interface between the shell-forming tissue and "material" precursors while these solidify and crystallize into hierarchical organic-inorganic biopolymer composites
(b) the need for establishing high-resolution and "close to in-vivo" imaging and high- contrast in-situ analysis techniques for hard/soft interfaces in "large", multicellular organisms and bio-engineered reporter systems
(c) the challenge of establishing conceptually novel material science driven approaches towards understanding the biological dynamics of transmembrane myosin chitin synthases, with their cytoskeleton-based signaling potential for regulating microvilli and extracellular pattern formation on multi-scale levels.
Considering sub-cellular dynamics as well as interfacial constraints in epithelially organized tissues, how does all this integrate with an increase in materials' performance, and the symmetry and coiling patterns of chitin/carbonate-based skeletons? Despite its complexity, mollusc shell formation is a highly robust process.
References
[1] Weiss, I.M. (2012) Z Krist, 227, 723-738.
[2] Weiss, I.M., Schönitzer, V., Eichner, N., Sumper, M. (2006) FEBS Lett, 580, 1846-1852.
[3] Weiss, I.M., Lüke, F., Eichner, N., Guth, C., Clausen-Schaumann, H. (2013) J Struct Biol, 183, 216- 225.
[4] Weiss, I.M., Marin, F. (2008) In: Sigel, A., Sigel, H., Sigel, R.K.O., eds. Metal Ions in Life Sciences - Biomineralization. Wiley, UK, 71-126.
