et al. 2006). Until recently, the classical paradigm was to consider that the control of
shell synthesis at the biocrystal scale was performed primarily by two main
mechanisms: crystal nucleation (and subsequent elongation) and growth inhibition
(Wheeler et al. 1988). New concepts and emerging models try now to translate a
more complex and dynamic reality, which is remarkably illustrated by the wide
variety of shell proteins, characterized in the last few years (Marin et al. 2008).
These proteins cover a broad spectrum of pI, from very acidic to very basic. The
primary structure of a number of them is composed of different modules, suggesting
that these proteins are multifunctional. Some of them exhibit enzymatic activities.
Others may be involved in cell signaling. Some others have remarkable crystalbinding properties. Nowadays, the extracellular calcifying shell matrix appears as a
whole integrated system, which regulates protein–mineral and protein–protein
interactions as well as feedback interactions between the biominerals and the
calcifying epithelium that synthesized them.
In the present paper, we focus on a peculiar model organism, Pinna nobilis, the
Mediterranean fan mussel. By many aspects, the choice of this species may appear
odd. This species cumulates indeed few handicaps: first, it is a strongly protected
species, a fact which does not facilitate field sampling; second, studies on the
physiology and reproduction of Pinna nobilis are sparse, and several field and
laboratory data have still to be generated on these topics; third, there are no extensive
genetic data available, and, as far as we know, there are no coming initiative aiming at
sequencing the genome, or, at least, aiming at obtaining transcriptomic data (ESTs).
At last, and this last fact explains the situation, the world scientific community, which
works – temporarily or full-time – on Pinna nobilis is extremely limited: a rough
estimation oscillates between two and three dozens of scientists on a world scale.
These obstacles would appear unsurmountable, if they were not compensated by the
fact that Pinna nobilis, from a historical viewpoint, is considered as a model organism
in biomineralization, in particular, by the production of its outer shell layer, made of
“regular simple calcitic prisms,” the structural and molecular characteristics of which
are detailed in the present review. Because the calcitic prisms of Pinna nobilis are
large and exhibit remarkable optical properties, they represent fascinating objects, for
trying to understand how molluscs are able to control their biocrystal synthesis over
molecular to millimeter scales. We believe that they may be a source of inspiration for
the analysis of structural hierarchy in biomineralization and for biomimicry purpose.
13.2 Pinna nobilis, a Model for Understanding Molluscan
Shell Formation
13.2.1 Presentation of Pinna nobilis
Also called noble pen mussel, rough pen shell, fan mussel, fan shell, razor fish, seawings or wing-shell, Pinna nobilis is the biggest Mediterranean bivalve, and
13 Acidic Shell Proteins of the Mediterranean Fan Mussel Pinna nobilis
355
shell synthesis at the biocrystal scale was performed primarily by two main
mechanisms: crystal nucleation (and subsequent elongation) and growth inhibition
(Wheeler et al. 1988). New concepts and emerging models try now to translate a
more complex and dynamic reality, which is remarkably illustrated by the wide
variety of shell proteins, characterized in the last few years (Marin et al. 2008).
These proteins cover a broad spectrum of pI, from very acidic to very basic. The
primary structure of a number of them is composed of different modules, suggesting
that these proteins are multifunctional. Some of them exhibit enzymatic activities.
Others may be involved in cell signaling. Some others have remarkable crystalbinding properties. Nowadays, the extracellular calcifying shell matrix appears as a
whole integrated system, which regulates protein–mineral and protein–protein
interactions as well as feedback interactions between the biominerals and the
calcifying epithelium that synthesized them.
In the present paper, we focus on a peculiar model organism, Pinna nobilis, the
Mediterranean fan mussel. By many aspects, the choice of this species may appear
odd. This species cumulates indeed few handicaps: first, it is a strongly protected
species, a fact which does not facilitate field sampling; second, studies on the
physiology and reproduction of Pinna nobilis are sparse, and several field and
laboratory data have still to be generated on these topics; third, there are no extensive
genetic data available, and, as far as we know, there are no coming initiative aiming at
sequencing the genome, or, at least, aiming at obtaining transcriptomic data (ESTs).
At last, and this last fact explains the situation, the world scientific community, which
works – temporarily or full-time – on Pinna nobilis is extremely limited: a rough
estimation oscillates between two and three dozens of scientists on a world scale.
These obstacles would appear unsurmountable, if they were not compensated by the
fact that Pinna nobilis, from a historical viewpoint, is considered as a model organism
in biomineralization, in particular, by the production of its outer shell layer, made of
“regular simple calcitic prisms,” the structural and molecular characteristics of which
are detailed in the present review. Because the calcitic prisms of Pinna nobilis are
large and exhibit remarkable optical properties, they represent fascinating objects, for
trying to understand how molluscs are able to control their biocrystal synthesis over
molecular to millimeter scales. We believe that they may be a source of inspiration for
the analysis of structural hierarchy in biomineralization and for biomimicry purpose.
13.2 Pinna nobilis, a Model for Understanding Molluscan
Shell Formation
13.2.1 Presentation of Pinna nobilis
Also called noble pen mussel, rough pen shell, fan mussel, fan shell, razor fish, seawings or wing-shell, Pinna nobilis is the biggest Mediterranean bivalve, and
13 Acidic Shell Proteins of the Mediterranean Fan Mussel Pinna nobilis
355