By crystallizing in vitro calcite in the presence of caspartin, Pokroy performed
X-ray diffraction measurements on the produced crystals. He evidenced a fifth
twinning plan, according to (108), which had never been observed before. The
results, which were published one year after the first one (Pokroy et al. 2007), have
passed largely unnoticed.
So far, it is difficult to measure the impact of such discoveries and their future
potential applications for nanotechnology and nanomaterials science. However,
from what has been described here above, it becomes clear that biocrystals, such
as the calcitic prisms of Pinna nobilis cannot be simply envisaged as “standard
chemical crystals with a little bit of organics around.”
13.5 Putative Functions of P. nobilis Shell Proteins: Toward
a Dynamic View of the Shell Fabrication
It would appear extremely ambitious – not to say risky – to explain how the
prismatic and nacreous layers of Pinna nobilis are formed, only with the a
posteriori knowledge of the ultrastructure of these layers, once formed, and only
with an extremely limited set of identified proteins. Indeed, for evident technical
reasons, there is no continuous record of the calcification process neither in
P. nobilis, neither in any other type of mollusc and we are limited to sample shells
at different growth stages and to check how they look like. Furthermore, we should
keep in mind that for a well-studied model, the pearl oyster Pinctada, more than
two dozens of shell proteins have been described so far (Marin et al. 2008), but this
is simply not sufficient to understand the emergence of calcitic prisms and brickwall
nacre of Pinctada shell. We do not have yet the key for understanding what happens
at the supramolecular level, and how shell matrix proteins interact with each other.
Worse, the transcriptomic analysis performed by Jackson and coworkers on
the abalone Haliotis asinina clearly suggests that the elaboration of the molluscan
shell microstructures requires some additional protein constituents that are not
incorporated in the shell during its growth (Jackson et al. 2006), and consequently,
do not belong to the shell matrix. These “silent” proteins may be extremely
important contributors to the shell fabrication but they are completely ignored
until now. In the case of Pinna nobilis, we do not have the slightest idea of what
these proteins could be, and only a transcriptomic approach (ESTs), performed on
actively calcifying mantle tissues, will tell us more about the complete cortege of
proteins required for shell formation.
In the absence of a complete theory on the mineralization of the molluscan shell,
we can only propose hypotheses that take in account geometrical, crystallographic,
and physiological constraints, as well as the biochemical properties of the secreted
matrices.
382
F. Marin et al.
X-ray diffraction measurements on the produced crystals. He evidenced a fifth
twinning plan, according to (108), which had never been observed before. The
results, which were published one year after the first one (Pokroy et al. 2007), have
passed largely unnoticed.
So far, it is difficult to measure the impact of such discoveries and their future
potential applications for nanotechnology and nanomaterials science. However,
from what has been described here above, it becomes clear that biocrystals, such
as the calcitic prisms of Pinna nobilis cannot be simply envisaged as “standard
chemical crystals with a little bit of organics around.”
13.5 Putative Functions of P. nobilis Shell Proteins: Toward
a Dynamic View of the Shell Fabrication
It would appear extremely ambitious – not to say risky – to explain how the
prismatic and nacreous layers of Pinna nobilis are formed, only with the a
posteriori knowledge of the ultrastructure of these layers, once formed, and only
with an extremely limited set of identified proteins. Indeed, for evident technical
reasons, there is no continuous record of the calcification process neither in
P. nobilis, neither in any other type of mollusc and we are limited to sample shells
at different growth stages and to check how they look like. Furthermore, we should
keep in mind that for a well-studied model, the pearl oyster Pinctada, more than
two dozens of shell proteins have been described so far (Marin et al. 2008), but this
is simply not sufficient to understand the emergence of calcitic prisms and brickwall
nacre of Pinctada shell. We do not have yet the key for understanding what happens
at the supramolecular level, and how shell matrix proteins interact with each other.
Worse, the transcriptomic analysis performed by Jackson and coworkers on
the abalone Haliotis asinina clearly suggests that the elaboration of the molluscan
shell microstructures requires some additional protein constituents that are not
incorporated in the shell during its growth (Jackson et al. 2006), and consequently,
do not belong to the shell matrix. These “silent” proteins may be extremely
important contributors to the shell fabrication but they are completely ignored
until now. In the case of Pinna nobilis, we do not have the slightest idea of what
these proteins could be, and only a transcriptomic approach (ESTs), performed on
actively calcifying mantle tissues, will tell us more about the complete cortege of
proteins required for shell formation.
In the absence of a complete theory on the mineralization of the molluscan shell,
we can only propose hypotheses that take in account geometrical, crystallographic,
and physiological constraints, as well as the biochemical properties of the secreted
matrices.
382
F. Marin et al.