possibly binds calcium and plays a role in inhibiting shell formation (Miyamoto
et al. 2005). Nacrein acts as a negative regulator in calcification by inhibiting the
precipitation of CaCO 3 in vitro (Miyamoto et al. 2005) and growth of an aragonitic
tablet in vivo (Gong et al. 2008c). Nacrein has been shown to be distributed within
aragonitic tablets and the intertabular matrix by immunolabeling (Gong et al.
2008c). Nacrein probably exists and functions as a complex P60 in nacreous
layer (Lao et al. 2007).
N16 is an acidic EDTA-insoluble nacreous matrix protein found in P. fucata
(Samata et al. 1999). Its homologues, Pearlin and N14, were identified from
P. fucata (Miyashita et al. 2000) and P. maxima (Kono et al. 2000), respectively.
The protein contains a sulfated mucopolysaccharide, with high proportions of Gly,
Tyr, and Asn together with NG repeat sequences. Its messenger RNA is expressed in
the dorsal region of the mantle as demonstrated by Northern blot analysis (Miyashita
et al. 2000). In vitro crystallization experiments revealed that N16-induced aragonite crystals once adsorbed onto the water-insoluble matrix membrane (Samata et al.
1999), and the mixture of N66 and N14 could induce flat aragonite layers very
similar to the nacreous layer under similar conditions (Kono et al. 2000). N-and
C-terminal sequence regions of N16 most likely play a key role in regulating the
crystal growth of calcium carbonate in the nacre layers (Kim et al. 2004). N16 is also
thought to act as a linker to connect with fibrion-like proteins and more highly acidic
proteins, and to participate in the formation of aragonite (Mann 2001).
Recently, an acidic nacreous matrix protein complex, Pif, has been identified
from P. fucata. It consists of Pif 97 and Pif 80, and specifically binds to aragonite
crystals. The results from immunolocalization, RNA interference, and in vitro
calcium carbonate crystallization experiments strongly indicate that Pif may aggregate with N16 and other proteins to regulate nacre formation (Suzuki et al. 2009).
Other known nacreous proteins include the positive regulator P10 (Zhang and
Zhang 2006), N40, and negative regulator alkaline N19 (Yano et al. 2007). Especially N40 is an exclusive protein that can nucleate aragonite by itself, without the
need for adsorption to a substrate. Thus, this study has proposed the possibility that
the nonacidic shell protein can also directly participate in aragonite nucleation and
even act as a nucleation site, which is different from earlier theories (Yan et al.
2007). Another acidic glycoprotein, ACCBP, purified from extrapallial fluid rather
than from nacre, could also modify the morphology of nacre lamellae by inhibiting
the growth of undesired aragonite crystal phases and meanwhile maintain the
stability of CaCO 3 -supersaturated body fluid by ceasing the nucleation and growth
of calcite (Ma et al. 2007).
Proteins from Abalone
Nacreous matrix proteins from the abalone Haliotis laevigata significantly differ
from those of pearl oysters. Most of them are alkaline, and possess unique
characteristics, such as the insulin-like growth factor binding protein Perlustrin
340
L.-p. Xie et al.
et al. 2005). Nacrein acts as a negative regulator in calcification by inhibiting the
precipitation of CaCO 3 in vitro (Miyamoto et al. 2005) and growth of an aragonitic
tablet in vivo (Gong et al. 2008c). Nacrein has been shown to be distributed within
aragonitic tablets and the intertabular matrix by immunolabeling (Gong et al.
2008c). Nacrein probably exists and functions as a complex P60 in nacreous
layer (Lao et al. 2007).
N16 is an acidic EDTA-insoluble nacreous matrix protein found in P. fucata
(Samata et al. 1999). Its homologues, Pearlin and N14, were identified from
P. fucata (Miyashita et al. 2000) and P. maxima (Kono et al. 2000), respectively.
The protein contains a sulfated mucopolysaccharide, with high proportions of Gly,
Tyr, and Asn together with NG repeat sequences. Its messenger RNA is expressed in
the dorsal region of the mantle as demonstrated by Northern blot analysis (Miyashita
et al. 2000). In vitro crystallization experiments revealed that N16-induced aragonite crystals once adsorbed onto the water-insoluble matrix membrane (Samata et al.
1999), and the mixture of N66 and N14 could induce flat aragonite layers very
similar to the nacreous layer under similar conditions (Kono et al. 2000). N-and
C-terminal sequence regions of N16 most likely play a key role in regulating the
crystal growth of calcium carbonate in the nacre layers (Kim et al. 2004). N16 is also
thought to act as a linker to connect with fibrion-like proteins and more highly acidic
proteins, and to participate in the formation of aragonite (Mann 2001).
Recently, an acidic nacreous matrix protein complex, Pif, has been identified
from P. fucata. It consists of Pif 97 and Pif 80, and specifically binds to aragonite
crystals. The results from immunolocalization, RNA interference, and in vitro
calcium carbonate crystallization experiments strongly indicate that Pif may aggregate with N16 and other proteins to regulate nacre formation (Suzuki et al. 2009).
Other known nacreous proteins include the positive regulator P10 (Zhang and
Zhang 2006), N40, and negative regulator alkaline N19 (Yano et al. 2007). Especially N40 is an exclusive protein that can nucleate aragonite by itself, without the
need for adsorption to a substrate. Thus, this study has proposed the possibility that
the nonacidic shell protein can also directly participate in aragonite nucleation and
even act as a nucleation site, which is different from earlier theories (Yan et al.
2007). Another acidic glycoprotein, ACCBP, purified from extrapallial fluid rather
than from nacre, could also modify the morphology of nacre lamellae by inhibiting
the growth of undesired aragonite crystal phases and meanwhile maintain the
stability of CaCO 3 -supersaturated body fluid by ceasing the nucleation and growth
of calcite (Ma et al. 2007).
Proteins from Abalone
Nacreous matrix proteins from the abalone Haliotis laevigata significantly differ
from those of pearl oysters. Most of them are alkaline, and possess unique
characteristics, such as the insulin-like growth factor binding protein Perlustrin
340
L.-p. Xie et al.