biomineralization are mainly for the construction of an organic framework, and the
control of the nucleation and growth of crystals.
12.4.1 Constructing the Organic Framework
Matrix proteins are one of the most important components of the organic framework in the nacreous layers of shell. These proteins have been conventionally
separated into “water-soluble” and “water-insoluble” fractions, according to their
solubility in aqueous solutions after decalcification with acid or EDTA (PereiraMouries et al. 2002). Generally, insoluble proteins, such as fibrion-like proteins
from Atrina nacre and MSI60 from Pinctada, participate in the construction of the
framework (together with chitin) on which the nucleation and growth of aragonite
crystals occur under the regulation of soluble matrix proteins (Addadi et al. 2006,
Nudelman et al. 2006). Moreover, intracrystalline organic matrix even forms the
network within aragonite crystal (Rousseau et al. 2005b), which is presumably
related with mediating nacre’s mechanical response. As well as acting as a framework, these proteins may have other functions which should be investigated in
future.
12.4.2 Controlling the Nucleation and Growth of Crystals
Acidic Asp-rich proteins on the organic sheet of the nacreous layer induce the
nucleation of aragonitic crystals (Weiner and Traub 1984; Addadi et al. 2006;
Nudelman et al. 2006). The fundamental principle governing nucleation of
crystals is interfacial molecular recognition at the surface of an organic matrix.
Because of molecular complementation between Ca atoms in the aragonite
ab face and aspartic acid residues organized in the Asp-X-Asp repeat domains
along the b-sheet matrix interface, aspartic acid residues play important roles
in Ca
2+ binding and oriented nucleation in shell nacre (Mann 2001). Acting
as a component of the nucleation site of the mineral crystals, acidic proteins
are more effective crystal modulators than other proteins from the same
biomineralized material (Fu et al. 2005). However, there is no direct correlation
between the acidity of soluble shell proteins and shell structure (Furuhashi
et al. 2010).
Some proteins induce the precipitation of aragonite crystals, such as N16
(Samata et al. 1999), P10 (Zhang et al. 2006), N40 (Yan et al. 2007), and Pif 80
protein (Suzuki et al. 2009) from P. fucata. N16 may also react with N66 (the
homologue of Nacrein from P. maxima) or aggregate with Pif 97 to promote the
nucleation of aragonite crystals (Kono et al. 2000; Suzuki et al. 2009). By contrast,
other nacreous matrix proteins inhibit the crystallization of CaCO 3 in vitro as a
342
L.-p. Xie et al.
control of the nucleation and growth of crystals.
12.4.1 Constructing the Organic Framework
Matrix proteins are one of the most important components of the organic framework in the nacreous layers of shell. These proteins have been conventionally
separated into “water-soluble” and “water-insoluble” fractions, according to their
solubility in aqueous solutions after decalcification with acid or EDTA (PereiraMouries et al. 2002). Generally, insoluble proteins, such as fibrion-like proteins
from Atrina nacre and MSI60 from Pinctada, participate in the construction of the
framework (together with chitin) on which the nucleation and growth of aragonite
crystals occur under the regulation of soluble matrix proteins (Addadi et al. 2006,
Nudelman et al. 2006). Moreover, intracrystalline organic matrix even forms the
network within aragonite crystal (Rousseau et al. 2005b), which is presumably
related with mediating nacre’s mechanical response. As well as acting as a framework, these proteins may have other functions which should be investigated in
future.
12.4.2 Controlling the Nucleation and Growth of Crystals
Acidic Asp-rich proteins on the organic sheet of the nacreous layer induce the
nucleation of aragonitic crystals (Weiner and Traub 1984; Addadi et al. 2006;
Nudelman et al. 2006). The fundamental principle governing nucleation of
crystals is interfacial molecular recognition at the surface of an organic matrix.
Because of molecular complementation between Ca atoms in the aragonite
ab face and aspartic acid residues organized in the Asp-X-Asp repeat domains
along the b-sheet matrix interface, aspartic acid residues play important roles
in Ca
2+ binding and oriented nucleation in shell nacre (Mann 2001). Acting
as a component of the nucleation site of the mineral crystals, acidic proteins
are more effective crystal modulators than other proteins from the same
biomineralized material (Fu et al. 2005). However, there is no direct correlation
between the acidity of soluble shell proteins and shell structure (Furuhashi
et al. 2010).
Some proteins induce the precipitation of aragonite crystals, such as N16
(Samata et al. 1999), P10 (Zhang et al. 2006), N40 (Yan et al. 2007), and Pif 80
protein (Suzuki et al. 2009) from P. fucata. N16 may also react with N66 (the
homologue of Nacrein from P. maxima) or aggregate with Pif 97 to promote the
nucleation of aragonite crystals (Kono et al. 2000; Suzuki et al. 2009). By contrast,
other nacreous matrix proteins inhibit the crystallization of CaCO 3 in vitro as a
342
L.-p. Xie et al.