Hic12, a novel acidic matrix protein promotes the transformation of calcite into vaterite in Hyriopsis cumingii

Shell acidic matrix proteins are widely considered to be essential for shell formation given their low affinity and high loading for calcium ion. In the present study, a novel matrix protein, hic12, was isolated from the mantle of Hyriopsis cumingii. High expression in tissue and positive signals with in situ hybridization were detected in the mantle center and mantle pallium, indicating that hic12 mainly participated in the biomineralization of the shell nacreous layer. The expression pattern of hic12 in the pearl sac during early pearl formation indicated that it was involved in pearl biomineralization. Moreover, the recombinant protein, rGST-Hic12, was successfully expressed and purified. The addition of rGST-Hic12 could accelerate the calcium carbonate deposition rate, change the morphology of crystals, and promote the conversion of calcite to vaterite. These results may provide new insights into the molecular mechanisms of aragonite mollusk shell formation.

1,1′-Ferrocenedicarboxylic acid/tetrahydrofuran induced precipitation of calcium carbonate with a multi-level structure in water

Multi-molecules co-regulate the orderly morphology and structure of CaCO3 precipitates and the influence of ether bonds on the formation of CaCO3 precipitates.

Amino Acid and Oligopeptide Effects on Calcium Carbonate Solutions

Biological organisms display sophisticated control of nucleation and crystallization of minerals. In order to mimic living systems, deciphering the mechanisms by which organic molecules control the formation of mineral phases from solution is a key step. We have used computer simulations to investigate the effects of the amino acids arginine, aspartic acid, and glycine on species that form in solutions of calcium carbonate (CaCO₃) at lower and higher levels of supersaturation. This provides net positive, negative, and neutral additives. In addition, we have prepared simulations containing hexapeptides of the amino acids to consider the effect of additive size on the solution species. We find that additives have limited impact on the formation of extended, liquid-like CaCO₃ networks in supersaturated solutions. Additives control the amount of (bi)carbonate in solution, but more importantly, they are able to stabilize these networks on the time scales of the simulations. This is achieved by coordinating the networks and assembled additive clusters in solutions. The association leads to subtle changes in the coordination of CaCO₃ and reduced mobility of the cations. We find that the number of solute association sites and the size and topology of the additives are more important than their net charge. Our results help to understand why polymer additives are so effective at stabilizing dense liquid CaCO₃ phases.

Anisotropic Epitaxial Behavior in the Amorphous Phase-Mediated Hydroxyapatite Crystallization Process: A New Understanding of Orientation Control

The precise control of crystallization is a key in the construction and engineering of crystalline materials, especially in biomineralization. Although it is generally accepted that biomineral crystals have evolved from their amorphous precursors, there are intense debates about crystallographic orientation control. By using in situ high-resolution transmission electron microscopy, we herein reveal that hydroxyapatite (HAP) is produced through its epitaxial growth from amorphous calcium phosphate with a preferential c-axis orientation. Abnormally but interestingly, this anisotropic epitaxial crystallization priority along the c-axis is not affected by the existing HAP crystalline substrate, which is exactly the same on either {002} or {100} facets. Molecular dynamics simulations suggest this preference is correlated with the interfacial energetic controls at the amorphous-crystalline transition frontier. The orientation control of biominerals here shows the key role of the interface energy, rather that the organic molecules or matrices, which provides a complementary understanding of the general c-axis orientation control of HAP in various biomineralization cases and aids in the development of an alternative strategy for crystallization control of functional materials.

Purification and functional analysis of the shell matrix protein N66 from the shell of the pearl oyster Pteria sterna

Mollusk biomineralization is a process controlled by a complex interplay of proteins, ions and external regulators. In spite of several studies, there is a lack of knowledge of who (molecules involved), how (mechanism) and why (evolution and adaptation) mollusk are designed as we know them. In this study, a shell matrix protein, N66, has been purified and characterized biochemically from the shell of Pteria sterna. Two protein bands with carbohydrates associated were separated with a molecular weight of ~60 and 64 kDa. It has carbonic anhydrase activity and it is able to form crystal polymorphs of calcium carbonate in vitro. The mRNA N66 was obtained from the mantle tissue of Pteria sterna and the deduced amino acid sequence contained a carbonic anhydrase (CA) domain and a Asn/Gly-rich domain (aa243-439). The CA domain contained three His residues acting as zinc ligands and the gate-keeper residues present in all α-CAs (Glu₁₆₆-Thr₅₂₅), being thus similar to the human isoform hCAVII. Also, to test whether the posttranslational modifications present on the native N66 affects the CA activity and its crystallization capability in vitro, a recombinant N66 was overexpressed in Escherichia coli and functionally characterized. Our results show that recombinant N66 has higher CA activity and produce larger size crystals in vitro than the native N66 protein, suggesting that intrinsic properties of the native N66, such as glycosylations and/or phosphorylations, might regulate its activity.

Biochemical and molecular characterization of N66 from the shell of Pinctada mazatlanica

Mollusk shell mineralization is a tightly controlled process made by shell matrix proteins (SMPs). However, the study of SMPs has been limited to a few model species. In this study, the N66 mRNA of the pearl oyster Pinctada mazatlanica was cloned and functionally characterized. The full sequence of the N66 mRNA comprises 1,766 base pairs, and encodes one N66 protein. A sequence analysis revealed that N66 contained two carbonic anhydrase (CA) domains, a NG domain and several glycosylation sites. The sequence showed similarity to the CA VII but also with its homolog protein nacrein. The native N66 protein was isolated from the shell and identified by mass spectrometry, the peptide sequence matched to the nucleotide sequence obtained. Native N66 is a glycoprotein with a molecular mass of 60–66 kDa which displays CA activity and calcium carbonate precipitation ability in presence of different salts. Also, a recombinant form of N66 was produced in Escherichia coli, and functionally characterized. The recombinant N66 displayed higher CA activity and crystallization capability than the native N66, suggesting that the lack of posttranslational modifications in the recombinant N66 might modulate its activity.

Electroextraction of Insoluble Proteins from the Organic Matrix of the Nacreous Layer of the Japanese Pearl Oyster, Pinctada fucata

The nacreous layer of shells and pearls is composed of aragonite crystals arranged in an organic matrix. The organic matrix contains chitin and several proteins that regulate the formation of the nacreous layer. Owing to their strong interactions in the organic matrix, the current method for extraction of insoluble proteins from the pre-powdered nacreous layer involves heating to high temperatures in the presence of a detergent (e.g., sodium dodecyl sulfate, SDS) and reductant (e.g., dithiothreitol, DTT), which is likely to induce protein degradation. Therefore, we have developed an electroextraction method to isolate proteins from the organic matrix of a nacreous organic sheet, that was obtained following the decalcification of shells in their original shape. Our electroextraction method employs milder conditions without heating or detergent. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of the electro-extracted proteins (EEPs) under non-reduced and reduced conditions revealed that this method yielded a greater number of different proteins compared with the conventional extraction method and the isolated EEPs retained their disulfide bonds. Our method is able to easily extract insoluble proteins from the nacreous layer under mild conditions and will undoubtedly aid future analyses into the functions of the nacreous layer proteins.

Droplet-based in situ X-ray absorption spectroscopy cell for studying crystallization processes at the tender X-ray energy range

The understanding of nucleation and crystallization is fundamental in science and technology. In solution, these processes are complex involving multiple transformations from ions and ion pairs through amorphous intermediates to multiple crystalline phases. X-ray absorption spectroscopy (XAS), which is sensitive to liquid, amorphous and crystalline phases offers prospects of demystifying these processes. However, for low Z elements the use of in situ X-ray absorption spectroscopy requires the tender X-ray range, which is often limited by vacuum requirements thereby complicating these measurements. To overcome these challenges, we developed a versatile and user-friendly droplet-based in situ X-ray absorption spectroscopy cell for studying crystallization processes. Time-resolved in situ experiments under ambient conditions are carried out in the cell whilst the cell is mounted in the vacuum chamber of a tender X-ray beamline. By following changes in the Ca K-edge X-ray absorption near edge structure (XANES), we captured in situ the intermediate phases involved during calcium carbonate crystallization from aqueous solutions. In addition, through linear combination fitting it was possible to qualitatively observe the evolution of each phase during the reaction demonstrating the potential of the cell in studying complex multiphase chemical processes.

We introduce a new in situ cell for time-resolved reactions involving aerosols/droplets using tender X-ray absorption spectroscopy and related methods.

A novel basic matrix protein of Pinctada fucata, PNU9, functions as inhibitor during crystallization of aragonite

The injection of dsRNA of PNU9 could lead to the overgrowth of nacreous lamellas and the matrix membrane.

Cloning, characterization and functional analysis of an Alveoline-like protein in the shell of Pinctada fucata

Shell matrix proteins (SMPs) have important functions in biomineralization. In the past decades, the roles of SMPs were gradually revealed. In 2015, our group identified 72 unique SMPs in Pinctada fucata, among which Alveoline-like (Alv) protein was reported to have homologous genes in Pinctada maxima and Pinctada margaritifera. In this study, the full-length cDNA sequence of Alv and the functional analysis of Alv protein during shell formation were explored. The deduced protein (Alv), which has a molecular mass of 24.9 kDa and an isoelectric point of 11.34, was characterized, and the functional analyses was explored in vivo and in vitro. The Alv gene has high expression in mantle and could response to notching damage. The functional inhibition of Alv protein in vivo by injecting recombinant Alv (rAlv) antibodies destroyed prism structure but accelerated nacre growth. Western blot and immunofluorescence staining showed that native Alv exists in the EDTA-insoluble matrix of both prismatic and nacreous layers and has different distribution patterns in the inner or outer prismatic layer. Taken together, the characterization and functional analyses of matrix protein Alv could expand our understanding of basic matrix proteins and their functions during shell formation.

A Novel Matrix Protein, PfY2, Functions as a Crucial Macromolecule during Shell Formation

Biomineralization, including shell formation, is dedicatedly regulated by matrix proteins. PfY2, a matrix protein detected in the ethylene diamine tetraacetic acid (EDTA)-soluble fraction from both prismatic layer and nacreous layer, was discovered by our group using microarray. It may play dual roles during biomineralization. However, the molecular mechanism is still unclear. In this research, we studied the function of PfY2 on crystallization in vivo and in vitro, revealing that it might be a negative regulator during shell formation. Notching experiment indicated that PfY2 was involved in shell repairing and regenerating process. Repression of PfY2 gene affected the structure of prismatic and nacreous layer simultaneously, confirming its dual roles in shell formation. Recombinant protein rPfY2 significantly suppressed CaCO₃ precipitation rate, participated in the crystal nucleation process, changed the morphology of crystals and inhibited the transformation of amorphous calcium carbonate (ACC) to stable calcite or aragonite in vitro. Our results may provide new evidence on the biomineralization inhibition process.

Functional Prioritization and Hydrogel Regulation Phenomena Created by a Combinatorial Pearl-Associated Two-Protein Biomineralization Model System

In the nacre or aragonitic layer of an oyster pearl, there exists a 12-member proteome that regulates both the early stages of nucleation and nanoscale-to-mesoscale assembly of nacre tablets and calcitic crystals from mineral nanoparticle precursors. Several approaches to understanding protein-associated mechanisms of pearl nacre formation have been developed, yet we still lack insight into how protein ensembles or proteomes manage nucleation and crystal growth. To provide additional insights, we have created a proportionally defined combinatorial model consisting of two pearl nacre-associated proteins, PFMG1 and PFMG2 (shell oyster pearl nacre, Pinctada fucata) whose individual in vitro mineralization functionalities are distinct from one another. Using scanning electron microscopy, atomic force microscopy, Ca(II) potentiometric titrations, and quartz crystal microbalance with dissipation monitoring quantitative analyses, we find that at 1:1 molar ratios, rPFMG2 and rPFMG1 co-aggregate in specific molecular ratios to form hybrid hydrogels that affect both the early and later stages of in vitro calcium carbonate nucleation. Within these hybrid hydrogels, rPFMG2 plays a role in defining protein co-aggregation and hydrogel dimension, whereas rPFMG1 defines participation in nonclassical nucleation processes; both proteins exhibit synergy with regard to surface and subsurface modifications to existing crystals. The interactions between both proteins are enhanced by Ca(II) ions and may involve Ca(II)-induced conformational events within the EF-hand rPFMG1 protein, as well as putative interactions between the EF-hand domain of rPFMG1 and the calponin-like domain of rPFMG2. Thus, the pearl-associated PFMG1 and PFMG2 proteins interact and exhibit mineralization functionalities in specific ways, which may be relevant for pearl formation.

Biomineralization: From Material Tactics to Biological Strategy

Biomineralization is an important tactic by which biological organisms produce hierarchically structured minerals with marvellous functions. Biomineralization studies typically focus on the mediation function of organic matrices on inorganic minerals, which helps scientists to design and synthesize bioinspired functional materials. However, the presence of inorganic minerals may also alter the native behaviours of organic matrices and even biological organisms. This progress report discusses the latest achievements relating to biomineralization mechanisms, the manufacturing of biomimetic materials and relevant applications in biological and biomedical fields. In particular, biomineralized vaccines and algae with improved thermostability and photosynthesis, respectively, demonstrate that biomineralization is a strategy for organism evolution via the rational design of organism-material complexes. The successful modification of biological systems using materials is based on the regulatory effect of inorganic materials on organic organisms, which is another aspect of biomineralization control. Unlike previous studies, this study integrates materials and biological science to achieve a more comprehensive view of the mechanisms and applications of biomineralization.

Incorporation of Human-Platelet-Derived Growth Factor-BB Encapsulated Poly(lactic-co-glycolic acid) Microspheres into 3D CORAGRAF Enhances Osteogenic Differentiation of Mesenchymal Stromal Cells

Tissue engineering aims to generate or facilitate regrowth or healing of damaged tissues by applying a combination of biomaterials, cells, and bioactive signaling molecules. In this regard, growth factors clearly play important roles in regulating cellular fate. However, uncontrolled release of growth factors has been demonstrated to produce severe side effects on the surrounding tissues. In this study, poly(lactic-co-glycolic acid) (PLGA) microspheres (MS) incorporated three-dimensional (3D) CORAGRAF scaffolds were engineered to achieve controlled release of platelet-derived growth factor-BB (PDGF-BB) for the differentiation of stem cells within the 3D polymer network. Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and microtomography were applied to characterize the fabricated scaffolds. In vitro study revealed that the CORAGRAF-PLGA-PDGF-BB scaffold system enhanced the release of PDGF-BB for the regulation of cell behavior. Stromal cell attachment, viability, release of osteogenic differentiation markers such as osteocalcin, and upregulation of osteogenic gene expression exhibited positive response. Overall, the developed scaffold system was noted to support rapid cell expansion and differentiation of stromal cells into osteogenic cells in vitro for bone tissue engineering applications.