Amorphous calcium carbonate: A precursor phase for aragonite in shell disease of the pearl oyster

Failure Mechanism of the Corrugated Medium under Simulated Cold Chain Logistics

It is necessary to develop corrugated medium food packaging, which is suitable for highly humid environments, to meet the demands of cold chain logistics. In this paper, we investigated the influence of the transverse ring crush index of different environmental factors of corrugated medium and the failure mechanisms during cold chain transportation. After freeze-thaw treatment of corrugated medium, XRD and DP showed a decrease in crystallinity and polymerization of 3.47 and 7.83%, respectively. Also, the FT-IR spectra of the paper showed that the number of intermolecular hydrogen bonds decreased by about 3.00% after freezing. SEM and XRD showed CaCO₃ precipitation on the paper surface and a 26.01% increase in pore size. This study would be beneficial in further expanding the applications of cellulose-based paperboard cold chain transportation.

An acidic protein, Hf15, from Haliotis fulgens involved in biomineralization

Biomineralization leads to the hardening of mineralized materials, such as the shell of Mollusk, to fulfill a wide range of functions, such as (but not limited to) skeletal support, protection of the soft tissues, navigation, etc. The study of the proteins responsible for this process, shell matrix proteins (SMPs), allows addressing questions related to structure-function relationship and to the mechanism of mineral formation, which is limited in gastropod species. In this study, a low molecular weight protein was isolated from the insoluble fraction after decalcification with acetic acid of the shell of Haliotis fulgens and, named Hf15. The unglycosylated protein has a theoretical molecular weight of 15 kDa, it possesses calcium and chiting binding properties. Hf15 can precipitate calcium carbonate in vitro in presence of different salts. Analysis by LC-MS of the five peptide sequences of Hf15 generated by trypsinization revealed that two peptides displayed homology to an uncharacterized protein 3-like from Haliotis rufescens, Haliotis asinia and H. sorenseni. The results obtained indicated that Hf15 is a novel SMP involved in shell mineralization in Haliotis fulgens.

Chemical and structural aspects of fresh and fossil marine mollusc shells investigated by mid-infrared and near-infrared spectroscopy with the support of statistical and multivariate methods

In the present study, we applied Fourier transform infrared (FTIR) and Fourier transform near infrared (FTNIR) spectroscopy to investigate some specific structural aspects of Patella caerulea, Mytilus edulis, Ostrea edulis, and Calista chione shells sampled in different sites. Moreover, for Ostrea edulis and Calista chione, the present study also included fossil samples. As far as FTIR spectroscopy is concerned, the support of statistical and multivariate methods such as the average spectrum (AV), spectral deconvolution, and two-dimensional correlation analysis (2DCOS) allowed to detect structural differences existing within the same mollusc species as a function of the sites they come. These differences can be reasonably linked to the local environmental conditions, which affect the biomineralization pattern of shell formation and growth. These structural differences are related to the calcite, aragonite, Mg-calcite contents, and interactions, as presently observed for fresh and fossil shells. The application of 2DCOS and deconvolution to FTIR spectra also showed the role of the amorphous calcium carbonate (ACC) in the structural characterization of shells, then suggesting the use of a new parameter, the calcite and aragonite to ACC (CAACC) ratio, as a new measurement for the structural characterization of shells. At last, FTNIR spectroscopy allowed detecting the presence of α-helix and β-sheet protein structures in the shells. The results of this study show that also FTIR and FTNIR spectroscopy are able to discern differences in structural characteristics of mollusc shells, a field of environmental studies where scanning electron microscopy and X-ray diffraction are the more widely used methods.

Ocean Acidification Alters Developmental Timing and Gene Expression of Ion Transport Proteins During Larval Development in Resilient and Susceptible Lineages of the Pacific Oyster (Crassostrea gigas)

Ocean acidification (OA) adversely impacts initial shell formation of bivalve larvae. Despite many studies observing large differences in developmental success between distinct genetic populations of bivalves exposed to OA, few studies have investigated the molecular mechanisms that enable resilient larvae to build their initial shell in aragonite-undersaturated conditions. This knowledge is key to their ecological and economical conservation. Herein, we used a genetic-selection program for Crassostrea gigas to produce a resilient and susceptible larval lineage to OA. The resilient and susceptible larvae were sampled every 3 h over a 24-h period in aragonite-undersaturated and control conditions. The susceptible lineage failed to develop a larval shell in aragonite-undersaturated conditions, whereas 52% of the resilient lineage developed to D-larvae by 24 h post fertilisation. We measured the expression of 23 genes involved in initial shell formation by RT-qPCR, which revealed significant genotype-by-time and environment-by-time interactions for the transcription of these genes. Aragonite-undersaturated conditions upregulated a single gene encoding a protein involved in ion transport, Na⁺ K⁺ ATPase, in both the resilient and susceptible lineage. These results were corroborated by a second experiment involving 25 pair-mated C. gigas families exposed to aragonite-undersaturated and control conditions. Our findings indicate C. gigas have a fixed capacity to modulate expression of genes involved in initial shell formation in response to OA. Thus, phenotypic differences to OA between the resilient and susceptible lineage are likely explained by other cellular processes, such as bioenergetics or protein translation.

A shell matrix protein of Pinctada mazatlanica produces nacre platelets in vitro

Nacre is the main component of the pearl oyster shells and it is synthesized by specialized soluble and insoluble shell matrix proteins. Insoluble proteins from the decalcification of the shell are the less studied proteins due to the technical problems to isolate them from the organic matrix. In this study, an insoluble shell matrix protein from Pinctada mazatlanica, pearlin (Pmaz-pearlin), was successfully cloned from the mantle tissue, and the native protein isolated from the shell was functionally characterized. The full coding sequence of Pmaz-pearlin mRNA consists of 423 base pairs, which encode to a 16.3 kDa pearlin. Analysis of the deduced amino acid sequence revealed that Pmaz-pearlin contained four acidic regions, an NG repeat domain, and Cys conserved residues, the latter potentially forms four disulfide bridges which might stabilize the protein structure. The isolated protein from the shell is a glycoprotein of ~ 16.74 kDa which can produce aragonite and calcite crystals in vitro. Our results show that Pmaz-pearlin is a well-conserved protein involved in nacre layer growth, which produces calcite crystals in the presence of CaCl2, aragonite crystal polymorphs with a hexagonal structure in the presence of MgCl2, and needle-like crystal structure polymorphs in the presence of CaCO3 The identity of the crystals was confirmed using RAMAN analyses.

Purification, crystallization and X-ray analysis of Pf-SCP (sarcoplasmic Ca-binding protein), related to storage and transport of calcium in mantle of Pinctada fucata

Pf-SCP, a 21 kDa protein with two EF-hand motifs and a phosphorylation site, was identified from mantle tissue and binds to calcium ions and transports calcium components from cell to the shell of Pinctada fucata. To reveal the molecular basis of the calcium binding activity of Pf-SCP, we expressed the recombinant protein of full-length Pf-SCP in Escherichia coli. Recombinant Pf-SCP (rPf-SCP) purified by Ni affinity chromatography and size exclusion chromatography appeared as a single band on SDS-PAGE. The circular dichroism spectroscopy showed that the α-helix content decreased when rPf-SCP interacted with both calcium ions and calcium carbonate. Western blotting and immunostaining verified the Pf-SCP expression in the shell and localization most in the mantle epithelial cells. To further understand the structural and functional regulation of Pf-SCP by calcium ions and calcium carbonate, the crystallization experiments of rPf-SCP in the presence of calcium ions were performed. A crystal of rPf-SCP obtained in the presence of calcium ions diffracted X-rays up to a resolution of 1.8 Å. The space group of the crystal is C2 with unit cell parameters of a = 96.828 Å, b = 55.906 Å, c = 102.14 Å and β = 90.009°, indicating that three molecules of rPf-SCP are contained in an asymmetric unit as estimated at the value of the Matthews coefficient. These results suggest that Pf-SCP may play a role in calcium ions transportation and shell mineralization by concentrating calcium ions inside the mantle epithelial cells and interacting with calcium carbonate molecules.

Cloning, characterization, and functional analysis of chitinase-like protein 1 in the shell of Pinctada fucata

Biomineralization, especially shell formation, is a sophisticated process regulated by various matrix proteins. Pinctada fucata chitinase-like protein 1 (Pf-Clp1), which belongs to the GH18 family, was discovered by our group using in-depth proteomic analysis. However, its function is still unclear. In this study, we first obtained the full-length cDNA sequence of Pf-Clp1 by RACE. Real-time polymerase chain reaction results revealed that Pf-Clp1 was highly expressed in the important biomineralization tissues, the mantle edge and the mantle pallial. We expressed and purified recombinant protein rPf-Clp1 in vitro to investigate the function of Pf-Clp1 on CaCO3 crystallization. Scanning electron microscopy imaging and Raman spectroscopy revealed that rPf-Clp1 was able to affect the morphologies of calcite crystal in vitro. Shell notching experiments suggested that Pf-Clp1 might function as a negative regulator during shell formation in vivo. Knockdown of Pf-Clp1 by RNAi led to the overgrowth of aragonite tablets, further confirming its potential negative regulation on biomineralization, especially in the nacreous layer. Our work revealed the potential function of molluscan Clp in shell biomineralization for the first time and unveiled some new understandings toward the molecular mechanism of shell formation.

A novel matrix protein PfX regulates shell ultrastructure by binding to specific calcium carbonate crystal faces

Here, we have identified a novel matrix protein, named PfX, from the pearl oyster Pinctada fucada, and investigated the effects of recombinant PfX protein on calcium carbonate crystallization. The expression of PfX was spatially concentrated in the mantle tissue and gill, the former of which is responsible for the formation of shell structures. The shell notching assay showed a PfX expression response during injured shell repair and regeneration, suggesting the potential involvement of this matrix protein in shell biomineralization. Further, an in vitro crystallization assay showed that PfX could alter the CaCO₃ morphologies of both calcite and aragonite polymorphs. Correspondingly, a binding assay indicated that PfX has strong binding affinity for CaCO₃ crystals, especially aragonite. Further, the protein's calcite binding capacity increased obviously when particular crystal faces were induced. In addition, PfX conjugated with fluorescent dye cyanine-5 (cy5) was preferentially distributed on rough crystal faces instead of the smooth and common (1 0 4) faces of calcite during the crystallization. These results suggest that matrix protein PfX might regulate CaCO₃ morphology via selective binding and inhibit the growth of certain crystal faces, providing new clues for understanding biomineralization mechanisms in mollusk.

Phase selection of calcium carbonate crystals under the induction of lignin monomer model compounds

The formation and application of ‘cinnamic acid & CaCO₃ crystals’ (CACs) induced by a lignin monomer compound.

Molecular and functional analysis of PmCHST1b in nacre formation of Pinctada fucata martensii

Keratan sulfate possesses considerable amounts of negatively charged sulfonic acid groups and participates in biomineralization. In the present study, we investigated characteristics and functions of a CHST1 gene identified from the pearl oyster Pinctada fucata martensii (PmCHST1b) which participated in the synthesis of keratan sulfate. PmCHST1b amino acid sequence carried a typical sulfotransferase-3 domain (sulfotransfer-3 domain) and belonged to membrane-associated sulfotransferases. Homologous analysis of CHST1 from different species showed the conserved motif (5' PSB motif and 3' PB motif) which interacted with 3'-phosphoadenosine-5'-phosphosulfate (PAPS). Structure analysis of sulfotransferase domain indicted that PmCHST1b showed the conserved catalytic structure character and the relationships presented in the phylogenetic tree conformed to that of traditional taxonomy. Expression pattern of PmCHST1b in different tissues and development stages showed that PmCHST1b widely expressed in all the detected tissues and development stages and showed the highest expression level in the central zone of mantle (MC). PmCHST1b expressed highly in the trochophore, D-stage larvae and spat which corresponded to prodissoconch and dissoconch shell formation, respectively. RNA interference (RNAi) successfully inhibited expression level of PmCHST1b in MC (P<0.05), and sulfate polymer content in the extrapallial fluid significantly reduced (P<0.05). Crystallization of shell nacre became irregular. Results above indicated that PmCHST1b may affect nacre formation by participating in synthesis of keratan sulfate in extrapallial fluid. This study provided fundamental materials for further research on the role of sulfotransferases and keratan sulfate in nacre formation.