The role of acidic phosphoproteins in biomineralization

Exploring the Potential of Nonclassical Crystallization Pathways to Advance Cementitious Materials

Understanding the crystallization of cement-binding phases, from basic units to macroscopic structures, can enhance cement performance, reduce clinker use, and lower CO2 emissions in the construction sector. This review examines the crystallization pathways of C-S-H (the main phase in PC cement) and other alternative binding phases, particularly as cement formulations evolve toward increasing SCMs and alternative binders as clinker replacements. We adopt a nonclassical crystallization perspective, which recognizes the existence of critical intermediate steps between ions in solution and the final crystalline phases, such as solute ion associates, dense liquid phases, amorphous intermediates, and nanoparticles. These multistep pathways uncover innovative strategies for controlling the crystallization of binding phases through additive use, potentially leading to highly optimized cement matrices. An outstanding example of additive-controlled crystallization in cementitious materials is the synthetically produced mesocrystalline C-S-H, renowned for its remarkable flexural strength. This highly ordered microstructure, which intercalates soft matter between inorganic and brittle C-S-H, was obtained by controlling the assembly of individual C-S-H subunits. While large-scale production of cementitious materials by a bottom-up self-assembly method is not yet feasible, the fundamental insights into the crystallization mechanism of cement binding phases presented here provide a foundation for developing advanced cement-based materials.

Structure of biomimetic casein micelles: Critical tests of the hydrophobic colloid and multivalent-binding models using recombinant deuterated and phosphorylated β-casein

Milk contains high concentrations of amyloidogenic casein proteins and is supersaturated with respect to crystalline calcium phosphates such as apatite. Nevertheless, the mammary gland normally remains unmineralized and free of amyloid. Unlike κ-casein, β- and αS-caseins are highly effective mineral chaperones that prevent ectopic and pathological calcification of the mammary gland. Milk invariably contains a mixture of two to five different caseins that act on each other as molecular chaperones. Instead of forming amyloid fibrils, several thousand caseins and hundreds of nanoclusters of amorphous calcium phosphate combine to form fuzzy complexes called casein micelles. To understand the biological functions of the casein micelle its structure needs to be understood better than at present. The location in micelles of the highly amyloidogenic κ-casein is disputed. In traditional hydrophobic colloid models, it, alone, forms a stabilizing surface coat that also determines the average size of the micelles. In the recent multivalent-binding model, κ-casein is present throughout the micelle, in intimate contact with the other caseins. To discriminate between these models, a range of biomimetic micelles was prepared using a fixed concentration of the mineral chaperone β-casein and nanoclusters of calcium phosphate, with variable concentrations of κ-casein. A biomimetic micelle was also prepared using a highly deuterated and in vivo phosphorylated recombinant β-casein with calcium phosphate and unlabelled κ-casein. Neutron and X-ray scattering experiments revealed that κ-casein is distributed throughout the micelle, in quantitative agreement with the multivalent-binding model but contrary to the hydrophobic colloid models.

Calcium carbonate polymorph selection in fish otoliths: A key role of phosphorylation of Starmaker-like protein

Fish otoliths are calcium carbonate biominerals found in the inner ear commonly used for tracking fish biochronologies and as a model system for biomineralization. The process of fish otolith formation is biologically controlled by numerous biomacromolecules which not only affect crystal size, shape, mechanical properties, but also selection of calcium carbonate polymorph (e.g., aragonite, vaterite). The proteinaceous control over calcium carbonate polymorph selection occurs in many other species (e.g., corals, mollusks, echinoderms) but the exact mechanism of protein interactions with calcium and carbonate ions - constituents of CaCO3 - are not fully elucidated. Herein, we focus on a native Starmaker-like protein isolated from vaterite asteriscus otoliths from Cyprinus carpio. The proteomic studies show the presence of the phosphorylated protein in vaterite otoliths. In a series of in vitro mineralization experiments with Starmaker-like, we show that native phosphorylation is a crucial determinant for the selection of a crystal's polymorphic form. This is the first report showing that the switch in calcium carbonate phase depends on the phosphorylation pattern of a single isolated protein. STATEMENT OF SIGNIFICANCE: Calcium carbonate has numerous applications in industry and medicine. However, we still do not understand the mechanism of biologically driven polymorph selection which results in specific biomineral properties. Previous work on calcium carbonate biominerals showed that either several macromolecular factors or high magnesium concentration (non-physiological) are required for proper polymorph selection (e.g., in mollusk shells, corals and otoliths). In this work, we showed for the first time that protein phosphorylation is a crucial factor for controlling the calcium carbonate crystal phase. This is important because a single protein from the otolith organic matrix could switch between polymorphs depending on the phosphorylation level. It seems that protein post-translational modifications (native, not artificial) are more important for biomolecular control of crystal growth than previously considered.

Autologous Tooth Graft: Innovative Biomaterial for Bone Regeneration. Tooth Transformer® and the Role of Microbiota in Regenerative Dentistry. A Systematic Review

Different biomaterials, from synthetic products to autologous or heterologous grafts, have been suggested for the preservation and regeneration of bone. The aim of this study is to evaluate the effectiveness of autologous tooth as a grafting material and examine the properties of this material and its interactions with bone metabolism. PubMed, Scopus, Cochrane Library, and Web of Science were searched to find articles addressing our topic published from 1 January 2012 up to 22 November 2022, and a total of 1516 studies were identified. Eighteen papers in all were considered in this review for qualitative analysis. Demineralized dentin can be used as a graft material, since it shows high cell compatibility and promotes rapid bone regeneration by striking an ideal balance between bone resorption and production; it also has several benefits, such as quick recovery times, high-quality newly formed bone, low costs, no risk of disease transmission, the ability to be performed as an outpatient procedure, and no donor-related postoperative complications. Demineralization is a crucial step in the tooth treatment process, which includes cleaning, grinding, and demineralization. Since the presence of hydroxyapatite crystals prevents the release of growth factors, demineralization is essential for effective regenerative surgery. Even though the relationship between the bone system and dysbiosis has not yet been fully explored, this study highlights an association between bone and gut microbes. The creation of additional scientific studies to build upon and enhance the findings of this study should be a future objective of scientific research.

Calcium interactions in amelogenin-derived peptide assembly

Phosphorylation of serine residues has been recognized as a pivotal event in the evolution of mineralized tissues in many biological systems. During enamel development, the extracellular matrix protein amelogenin is most abundant and appears to be critical to the extreme high aspect ratios (length:width) of apatite mineral fibers reaching several millimeters in larger mammalian teeth. A 14-residue peptide (14P2, residues Gly8 to Thr21) was previously identified as a key sequence mediating amelogenin assembly formation, the domain also contains the native single phosphoserine residue (Ser16) of the full-length amelogenin. In this research, 14P2 and its phosphorylated form (p14P2) were investigated at pH 6.0 with various calcium and phosphate ion concentrations, indicating that both peptides could self-assemble into amyloid-like conformation but with differences in structural details. With calcium, the distance between ³¹P within the p14P2 self-assemblies is averaged to be 4.4 ± 0.2Å, determined by solid-state NMR ³¹P PITHIRDS-CT experiments. Combining with other experimental results, solid-state Nuclear Magnetic Resonance (SSNMR) suggests that the p14P2 self-assemblies are in parallel in-register β-sheet conformation and divalent calcium ions most likely connect two adjacent peptide chains by binding to the phosphate group of Ser16 and the carboxylate of Glu18 side-chain. This study on the interactions between calcium ions and amelogenin-derived peptides provides insights on how amelogenin may self-assemble in the presence of calcium ions in early enamel development.

Highly acidic pH facilitates enamel protein self-assembly, apatite crystal growth and enamel protein interactions in the early enamel matrix

Tooth enamel develops within a pH sensitive amelogenin-rich protein matrix. The purpose of the present study is to shed light on the intimate relationship between enamel matrix pH, enamel protein self-assembly, and enamel crystal growth during early amelogenesis. Universal indicator dye staining revealed highly acidic pH values (pH 3-4) at the exocytosis site of secretory ameloblasts. When increasing the pH of an amelogenin solution from pH 5 to pH 7, there was a gradual increase in subunit compartment size from 2 nm diameter subunits at pH 5 to a stretched configuration at pH6 and to 20 nm subunits at pH 7. HSQC NMR spectra revealed that the formation of the insoluble amelogenin self-assembly structure at pH6 was critically mediated by at least seven of the 11 histidine residues of the amelogenin coil domain (AA 46-117). Comparing calcium crystal growth on polystyrene plates, crystal length was more than 20-fold elevated at pH 4 when compared to crystals grown at pH 6 or pH 7. To illustrate the effect of pH on enamel protein self-assembly at the site of initial enamel formation, molar teeth were immersed in phosphate buffer at pH4 and pH7, resulting in the formation of intricate berry tree-like assemblies surrounding initial enamel crystal assemblies at pH4 that were not evident at pH7 nor in citrate buffer. Amelogenin and ameloblastin enamel proteins interacted at the secretory ameloblast pole and in the initial enamel layer, and co-immunoprecipitation studies revealed that this amelogenin/ameloblastin interaction preferentially takes place at pH 4-pH 4.5. Together, these studies highlight the highly acidic pH of the very early enamel matrix as an essential contributing factor for enamel protein structure and self-assembly, apatite crystal growth, and enamel protein interactions.

The Role of Intrinsically Disordered Proteins in Liquid–Liquid Phase Separation during Calcium Carbonate Biomineralization

Some animal organs contain mineralized tissues. These so-called hard tissues are mostly deposits of calcium salts, usually in the form of calcium phosphate or calcium carbonate. Examples of this include fish otoliths and mammalian otoconia, which are found in the inner ear, and they are an essential part of the sensory system that maintains body balance. The composition of ear stones is quite well known, but the role of individual components in the nucleation and growth of these biominerals is enigmatic. It is sure that intrinsically disordered proteins (IDPs) play an important role in this aspect. They have an impact on the shape and size of otoliths. It seems probable that IDPs, with their inherent ability to phase separate, also play a role in nucleation processes. This review discusses the major theories on the mechanisms of biomineral nucleation with a focus on the importance of protein-driven liquid–liquid phase separation (LLPS). It also presents the current understanding of the role of IDPs in the formation of calcium carbonate biominerals and predicts their potential ability to drive LLPS.

Nanomechanical Characterization of Enzyme Induced Carbonate Precipitates

The mechanical properties of calcium carbonate minerals formed by enzyme-induced carbonate precipitation (EICP) were studied using nanoindentation. Two types of precipitates were considered: (i) a “baseline” precipitate, synthesized via urea hydrolysis in an aqueous solution of urease enzyme, urea, and calcium chloride; and (ii) a “modified” precipitate, synthesized from a similar solution, but with the inclusion of nonfat dry milk. While both precipitates predominantly comprised calcite, X-ray diffraction and Raman spectroscopy indicated broader peaks in the modified precipitate, implying differences in the crystal structure of the two precipitates. Both precipitates were polycrystalline and had a higher average indentation hardness (H) and a lower indentation modulus (M) compared with the values for single calcite crystals reported in the literature. The ductility of the precipitates was quantified by the ratio M/H. The modified precipitate had a higher average M/H, implying greater ductility. The increased ductility of the modified precipitate results in higher resistance to crack propagation. In sands biocemented using the modified EICP solution, the increased ductility of the precipitate, in addition to preferential precipitation at interparticle contacts, may contribute to relatively high unconfined compressive strengths at low carbonate contents.

Review: Post-translational modifications of marine shell matrix proteins

Shell matrix proteins (SMPs) are key components for the Mollusk shell biomineralization. SMPs function has been hypothesized in several proteins by bioinformatics analysis, and through in vitro crystallization assays. However, studies of the post-translational modifications (PTMs) of SMPs, which contribute to their structure and the function, are limited. This review provides the current status of the SMPs with the most common PTMs described (glycosylation, phosphorylation, and disulfide bond formation) and their role in shell biomineralization. Also, recent studies based on recombinant production of SMPs are discussed. Finally, recommendations for the study of SMPs and their PTMs are provided. The review showed that PTMs are widely distributed in SMPs, and their presence on SMPs may contribute to the modulation of their activity in some SMPs, contributing to the crystal growth formation and differentiation through different mechanisms, however, in a few cases the lack of the PTMs do not alter their inherent function.

Exploring the interplay of mucin with biologically-relevant amorphous magnesium-calcium phosphate nanoparticles

HYPOTHESIS

It has been recently shown that, in our organism, the secretions of Ca²⁺, Mg²⁺ and phosphate ions lead to the precipitation of amorphous magnesium-calcium phosphate nanoparticles (AMCPs) in the small intestine, where the glycoprotein mucin is one of the most abundant proteins, being the main component of the mucus hydrogel layer covering gut epithelium. Since AMCPs precipitate in vivo in a mucin-rich environment, we aim at studying the effect of this glycoprotein on the formation and features of endogenous-like AMCPs.

EXPERIMENTS

AMCPs were synthesized from aqueous solution in the presence of different concentrations of mucin, and the obtained particles were characterised in terms of crystallinity, composition and morphology. Solid State NMR investigation was also performed in order to assess the interplay between mucin and AMCPs at a sub-nanometric level.

FINDING

Results show that AMCPs form in the presence of mucin and the glycoprotein is efficiently incorporated in the amorphous particles. NMR indicates the existence of interactions between AMCPs and mucin, revealing how AMCPs in mucin-hybrid nanoparticles affect the features of both proteic and oligosaccharidic portions of the glycoprotein. Considering that the primary function of mucin is the protection of the intestine from pathogens, we speculate that the nature of the interaction between AMCPs and mucin described in the present work might be relevant to the immune system, suggesting a novel type of scenario which could be investigated by combining physico-chemical and biomedical approaches.

[The latest study on biomimetic mineralized collagen-based bone materials for pediatric skull regeneration and repair]

As a worldwide challenge in the field of neurosurgery, there is no effective treatment method for pediatric skull defects repair in clinic. Currently clinical used cranioplasty materials couldn't undergo adjustment in response to skull growth and deformation. An ideal material for pediatric cranioplasty should fulfill the requirements of achieving complete closure, good osseointegration, biodegradability and conformability, sufficient cerebral protection and optimal aesthetic, and functional restoration of calvaria. Biomimetic mineralized collagen-based bone material is a kind of material that simulates the microstructural unit of natural bone on the nanometer scale. Because of its high osteogenic activity, it is widely used in repair of all kinds of bone defects. Recently, the biomimetic mineralized collagen-based bone materials have successfully been applied for cranial regeneration and repair with satisfactory results. This review mainly introduces the characteristics of the biomimetic mineralized collagen-based bone materials, the advantages for the repair of pediatric skull defects, and the related progresses.

Recombinant transgelin-like protein 1 from Mytilus shell induces formation of CaCO3 polymorphic crystals in vitro

Transgelin is an actin cross-linking/gelling protein of the calponin family, which is associated with actin stress fibres, cell motility, adhesion and the maintenance of cell morphology. Transgelin-like proteins (TLPs) have also been identified as shell matrix proteins (SMPs) in several mollusc species; however, the functions of TLPs in biomineralization remain unknown. Transgelin-like protein 1 (TLP-1) was previously identified from the shell of Mytilus coruscus as a novel 19 kDa SMP with a calponin homology (CH) domain. To understand the role of TLP-1 in shell formation, the expression level and localization of the TLP-1 gene in biomineralization-related tissues were determined in this study. Furthermore, recombinant TLP-1 was expressed in a prokaryotic expression system with codon optimization, and an anti-rTLP-1 antibody was prepared based on the expressed recombinant TLP-1 (rTLP-1) protein. In vitro, rTLP-1 induced the formation of CaCO3 polymorphic crystals with distinct morphologies and inhibited crystallization rate and crystal interactions. Immunohistochemical, immunofluorescence, and pull-down analyses using the anti-rTLP-1 antibody revealed the specific locations of TLP-1 in biomineralization-related tissues and shell myostracum layer, and suggested the existence of a possible TLP-1 interaction network in the shell matrix. Our results are beneficial for understanding the functions of TLP-1, particularly through its CH domain, during shell mineralization.

Structural Biology of Calcium Phosphate Nanoclusters Sequestered by Phosphoproteins

Biofluids that contain stable calcium phosphate nanoclusters sequestered by phosphopeptides make it possible for soft and hard tissues to co-exist in the same organism with relative ease. The stability diagram of a solution of nanocluster complexes shows how the minimum concentration of phosphopeptide needed for stability increases with pH. In the stable region, amorphous calcium phosphate cannot precipitate. Nevertheless, if the solution is brought into contact with hydroxyapatite, the crystalline phase will grow at the expense of the nanocluster complexes. The physico-chemical principles governing the formation, composition, size, structure, and stability of the complexes are described. Examples are given of complexes formed by casein, osteopontin, and recombinant phosphopeptides. Application of these principles and properties to blood serum, milk, urine, and resting saliva is described to show that under physiological conditions they are in the stable region of their stability diagram and so cannot cause soft tissue calcification. Stimulated saliva, however, is in the metastable region, consistent with its role in tooth remineralization. Destabilization of biofluids, with consequential ill-effects, can occur when there is a failure of homeostasis, such as an increase in pH without a balancing increase in the concentration of sequestering phosphopeptides.

Mineralization of calcium phosphate controlled by biomimetic self-assembled peptide monolayers via surface electrostatic potentials

The functions of acidic-rich domains in non-collagenous protein during biomineralization are thought to induce nucleation and control the growth of hydroxyapatite. The tripeptide Asp-Ser-Ser (DSS) repeats are the most common acidic-rich repeated unit in non-collagenous protein of dentin phosphoprotein, the functions of which have aroused extensive interests. In this study, biomimetic peptides (DSS)_n (n = 2 or 3) were designed and fabricated into self-assembled monolayers (SAMs) on Au (111) surface as biomimetic organic templates to regulate hydroxyapatite (HAp) mineralization in 1.5 simulated body fluid (1.5 SBF) at 37 °C. The early mineralization processes and minerals deposited on the SAMs were characterized by X-ray diffraction, scanning electron microscope, and Fourier transform infrared spectroscopy analyses. The SAM-DSS9/DSS9G showed the highest capacity to induce HAp nucleation and growth, followed by SAM-DSS6/DSS6G, SAM-COOH, and SAM-OH. The SAM-(DSS)_n had more negative zeta potentials than SAM-COOH surface, indicating that DSS repeats contributed to the biomineralization, which not only provided strong affinity with Ca²⁺ ions through direct electrostatic bonds, but more importantly influence surface electrostatic potentials of the assembled organic template for nucleation.

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Biomimetic peptides designed from DPP and self-assembled to form SAMs.

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Quantitative model for HAp mineralization regulated by non-collagenous protein.

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Extra DSS repeat reduced the zeta potential on the SAM surface.

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The nuclei quantity and mineral size on DSS9/DSS9G were always larger.

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DSS repeats provided surface electrostatic potentials for stronger Ca²⁺ affinity.

Coral acid rich protein selects vaterite polymorph in vitro

Corals and other biomineralizing organisms use proteins and other molecules to form different crystalline polymorphs and biomineral structures. In corals, it’s been suggested that proteins such as Coral Acid Rich Proteins (CARPs) play a major role in the polymorph selection of their calcium carbonate (CaCO₃) aragonite exoskeleton. To date, four CARPs (1–4) have been characterized: each with a different amino acid composition and different temporal and spatial expression patterns during coral developmental stages. Interestingly, CARP3 is able to alter crystallization pathways in vitro, yet its function in this process remains enigmatic. To better understand the CARP3 function, we performed two independent in vitro CaCO₃ polymorph selection experiments using purified recombinant CARP3 at different concentrations and at low or zero Mg²⁺ concentration. Our results show that, in the absence of Mg²⁺, CARP3 selects for the vaterite polymorph and inhibits calcite. However, in the presence of a low concentration of Mg²⁺ and CARP3 both Mg-calcite and vaterite are formed, with the relative amount of Mg-calcite increasing with CARP3 concentration. In all conditions, CARP3 did not select for the aragonite polymorph, which is the polymorph associated to CARP3 in vivo, even in the presence of Mg²⁺ (Mg:Ca molar ratio equal to 1). These results further emphasize the importance of Mg:Ca molar ratios similar to that in seawater (Mg:Ca equal to 5) and the activity of the biological system in a aragonite polymorph selection in coral skeleton formation.

PI3K inhibition highlights new molecular interactions involved in the skeletogenesis of Paracentrotus lividus embryos

The sea urchin embryo develops a well-defined biomineralized endoskeleton, synthesized exclusively by the skeletogenic cells, supported by ectodermal cues for the correct skeleton patterning. The biomineralization process is tightly regulated via a hierarchical order of gene expression, including transcription and growth factors, biomineralization proteins. Recently, the role of kinases and intracellular signaling pathways in sea urchin skeletogenesis has been addressed, although the downstream components still remain unknown. In this study, we investigated the role of phosphatidylinositide 3-kinase (PI3K)-mediated signaling pathway in Paracentrotus lividus, to identify its genes/proteins targets. The effects of LY294002 (LY), a PI3K-specific inhibitor, were evaluated at morphological and molecular levels. Treatment with 40 μM LY from the blastula stage completely blocked skeleton deposition, which was reversed by wash out experiments. Besides, LY caused a slight delay in the tripartite gut development. Despite the skeleton absence, a few skeleton-specific proteins/mRNAs were regularly expressed and localized in LY-treated embryos, as shown for MSP130 and SM50 by immunofluorescence and in situ hybridization experiments. QPCR analyses showed that LY differently affected the expression of genes coding for other biomineralization proteins, transcription and growth factors. SM30 and carbonic anhydrase expression was severely downregulated, while almost all the transcription factors analyzed were upregulated. Based on the present results and in silico analyses, we propose an "interactomic" model simulating PI3K connections in P. lividus embryos. Our findings define a novel regulatory step in the embryonic skeletogenesis, and provide valuable molecular data for further studies on the role of PI3K signaling in invertebrate biomineralization.

In vivo and in vitro analysis of starmaker activity in zebrafish otolith biomineralization

Otoliths are one of the biominerals whose formation is highly controlled by proteins. The first protein discovered to be involved in otolith biomineralization in zebrafish was starmaker (Stm). Previously, Stm was shown to be responsible for the preferential formation of aragonite, a polymorph of calcium carbonate, in otoliths. In this work, proteomic analysis of adult zebrafish otoliths was performed. Stm is the only highly phosphorylated protein found in our studies. Besides previously studied otolith proteins, we discovered several dozens of unknown proteins that reveal the likely mechanism of biomineralization. A comparison of aragonite and vaterite otoliths showed similarities in protein composition. We observed the presence of Stm in both types of otoliths. In vitro studies of 2 characteristic Stm fragments indicated that the DS-rich region has a special biomineralization activity, especially after phosphorylation.-Kalka, M., Markiewicz, N., Ptak, M., Sone, E. D., Ożyhar, A., Dobryszycki, P., Wojtas, M. In vivo and in vitro analysis of starmaker activity in zebrafish otolith biomineralization.

Comparison of the organic matrix found in intestinal CaCO3 precipitates produced by several marine teleost species

Marine bony fish poses the unique ability to hydrate from imbibed seawater. They accomplish this, in part, by the precipitation of inorganic carbonate mineral in their intestine, which lowers luminal osmotic pressure and allows for water uptake. It has recently been described that in the Gulf toadfish (Opsanus beta) this Ca(Mg)CO₃ precipitation occurs under the regulation of an organic matrix. To date no investigations have aimed to determine if this phenomenon applies more generally to marine fish. Here, intestinally derived precipitates were collected from gray snapper (Lutjanus griseus), white grunt (Haemulon plumieri), European flounder (Platichthys flesus), as well as Gulf toadfish, and their matrices were extracted. The ability of these matrices to regulate CaCO₃ production was determined using an in vitro calcification assay, which revealed that the matrix derived from each of the tested species increased precipitation at low concentrations, while inhibiting it at higher concentrations in full agreement with the earlier studies on toadfish. Matrix extracted from European flounder precipitates was then analyzed by mass spectrometry, leading to the identification of over 50 unique proteins. When the identities of these proteins were compared to previous investigation of toadfish precipitate matrix, nearly 35% were found to overlap between the flounder and toadfish analyses, suggesting conserved mechanisms of precipitation control. The effects of using different sodium hypochlorite (NaOCl) solutions during precipitate purification on the resulting organic matrix are also discussed.

Titanium surface bio-functionalization using osteogenic peptides: Surface chemistry, biocompatibility, corrosion and tribocorrosion aspects

Titanium (Ti) is widely used in biomedical devices due to its recognized biocompatibility. However, implant failures and subsequent clinical side effects are still recurrent. In this context, improvements can be achieved by designing biomaterials where the bulk and the surface of Ti are independently tailored. The conjugation of biomolecules onto the Ti surface can improve its bioactivity, thus accelerating the osteointegration process. Ti was modified with TiO₂, two different spacers, 3-(4-aminophenyl) propionic acid (APPA) or 3-mercaptopropionic acid (MPA) and dentin matrix protein 1 (DMP1) peptides. X-ray photoelectron spectroscopy analysis revealed the presence of carbon and nitrogen for all samples, indicating a success in the functionalization process. Furthermore, DMP1 peptides showed an improved coverage area for the samples with APPA and MPA spacers. Biological tests indicated that the peptides could modulate cell affinity, proliferation, and differentiation. Enhanced results were observed in the presence of MPA. Moreover, the immobilization of DMP1 peptides through the spacers led to the formation of calcium phosphate minerals with a Ca/P ratio near to that of hydroxyapatite. Corrosion and tribocorrosion results indicated an increased resistance to corrosion and lower mass loss in the functionalized materials, showing that this new type of functional material has attractive properties for biomaterials application.

Influences of LaCl3 on the mineral phase transformation during osteoblast mineralization in vitro

Rat calvarial osteoblasts were treated with lanthanum chloride (LaCl₃) to explore its effect on the mineral crystalline phase during the process of osteoblast calcification in vitro. The results confirmed that La was readily deposited in the mineral component of the matrix. Employing high-resolution transmission electron microscopy and Fourier transform infrared microspectroscopy techniques, we demonstrated that features comparable to dicalcium phosphate dihydrate (DCPD) and octacalcium phosphate, and hydroxyapatite (HAP) were detected in the mineral phases in vitro. Particularly, LaCl₃ treatment retarded conversion from DCPD-like phase into HAP during mineralization. In addition, La was introduced in DCPD powder during wet chemical synthesis. When compared with that of La-free DCPD, the dissolution rate of La-incorporated DCPD was lower, thereby leading to a delayed DCPD-to-HAP phase transformation. Thus, it can be concluded that LaCl₃ treatment influences the kinetics of inorganic phase transition by decreasing the dissolution rate of DCPD.

A proteinaceous organic matrix regulates carbonate mineral production in the marine teleost intestine

Marine teleost fish produce CaCO₃ in their intestine as part of their osmoregulatory strategy. This precipitation is critical for rehydration and survival of the largest vertebrate group on earth, yet the molecular mechanisms that regulate this reaction are unknown. Here, we isolate and characterize an organic matrix associated with the intestinal precipitates produced by Gulf toadfish (Opsanus beta). Toadfish precipitates were purified using two different methods, and the associated organic matrix was extracted. Greater than 150 proteins were identified in the isolated matrix by mass spectrometry and subsequent database searching using an O. beta transcriptomic sequence library produced here. Many of the identified proteins were enriched in the matrix compared to the intestinal fluid, and three showed no substantial homology to any previously characterized protein in the NCBI database. To test the functionality of the isolated matrix, a micro-modified in vitro calcification assay was designed, which revealed that low concentrations of isolated matrix substantially promoted CaCO₃ production, where high concentrations showed an inhibitory effect. High concentrations of matrix also decreased the incorporation of magnesium into the forming mineral, potentially providing an explanation for the variability in magnesium content observed in precipitates produced by different fish species.

The calcified eggshell matrix proteome of a songbird, the zebra finch (Taeniopygia guttata)

Background

The proteins of avian eggshell organic matrices are thought to control the mineralization of the eggshell in the shell gland (uterus). Proteomic analysis of such matrices identified many candidates for such a role. However, all matrices analyzed to date come from species of one avian family, the Phasianidae. To analyze the conservation of such proteins throughout the entire class Aves and to possibly identify a common protein toolkit enabling eggshell mineralization, it is important to analyze eggshell matrices from other avian families. Because mass spectrometry-based in-depth proteomic analysis still depends on sequence databases as comprehensive and accurate as possible, the obvious choice for a first such comparative study was the eggshell matrix of zebra finch, the genome sequence of which is the only songbird genome published to date.

Results

The zebra finch eggshell matrix comprised 475 accepted protein identifications. Most of these proteins (84 %) were previously identified in species of the Phasianidae family (chicken, turkey, quail). This also included most of the so-called eggshell-specific proteins, the ovocleidins and ovocalyxins. Ovocleidin-116 was the second most abundant protein in the zebra finch eggshell matrix. Major proteins also included ovocalyxin-32 and -36. The sequence of ovocleidin-17 was not contained in the sequence database, but a presumptive homolog was tentatively identified by N-terminal sequence analysis of a prominent 17 kDa band. The major proteins also included three proteins similar to ovalbumin, the most abundant of which was identified as ovalbumin with the aid of two characteristic phosphorylation sites. Several other proteins identified in Phasianidae eggshell matrices were not identified. When the zebra finch sequence database contained a sequence similar to a missing phasianid protein it may be assumed that the protein is missing from the matrix. This applied to ovocalyxin-21/gastrokine-1, a major protein of the chicken eggshell matrix, to EDIL3 and to lactadherin. In other cases failure to identify a particular protein may be due to the absence of this protein from the sequence database, highlighting the importance of better, more comprehensive sequence databases.

Conclusions

The results indicate that ovocleidin-116, ovocleidin-17, ovocalyxin-36 and ovocalyxin-32 may be universal avian eggshell-mineralizing proteins. All the more important it is to elucidate the role of these proteins at the molecular level. This cannot be achieved by proteomic studies but will need application of other methods, such as atomic force microscopy or gene knockouts. However, it will also be important to analyze more eggshell matrices of different avian families to unequivocally identify other mineralization toolkit proteins apart from ovocleidins and ovocalyxins. Progress in this respect will depend critically on the availability of more, and more comprehensive, sequence databases. The development of faster and cheaper nucleotide sequencing methods has considerably accelerated genome and transcriptome sequencing, but this seems to concur with frequent publication of incomplete and fragmented sequence databases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-015-0086-1) contains supplementary material, which is available to authorized users.

Expression of the invertebrate sea urchin P16 protein into mammalian MC3T3 osteoblasts transforms and reprograms them into "osteocyte-like" cells

P16 is an acidic phosphoprotein important in both sea urchin embryonic spicule development and transient mineralization during embryogenesis, syncytium formation, and mineralization in mature urchin tooth. Anti-P16 has been used to localize P16 to the syncytial membranes and the calcite mineral. Specific amino acid sequence motifs in P16 are similar to sequences in DSPP, a protein common to all vertebrate teeth, and crucial for their mineralization. Here, we examine the effect of P16 on vertebrate fibroblastic NIH3T3 cells and osteoblastic MC3T3 cells. Transfection of NIH3T3 cells with P16 cDNA resulted in profound changes in the morphology of the cells. In culture, the transfected cells sent out long processes that contacted processes from neighboring cells forming networks or syncytia. There was a similar change in morphology in cultured osteoblastic MC3T3 cells. In addition, the MC3T3 developed numerous dendrites as found in osteocytes. Importantly, there was also a change in the expression of the osteoblast and osteocyte specific genes. MC3T3 cells transfected with P16 showed an 18-fold increase in expression of the osteocyte specific Dentin matrix protein (DMP1) gene, accompanied by decreased expression of osteoblast specific genes: Bone sialoprotein (BSP), osteocalcin (OCN), and β-catenin decreased by 70%, 64%, and 68 %, respectively. Thus, invertebrate urchin P16 with no previously known analog in vertebrates was able to induce changes in both cell morphology and gene expression, converting vertebrate-derived osteoblast-like precursor cells to an "osteocyte-like" phenotype, an important process in bone biology. The mechanisms involved are presently under study.

Proteomic analysis of quail calcified eggshell matrix: a comparison to chicken and turkey eggshell proteomes

Background

Eggshell mineralization in commercially important species such as chicken, turkey or quail is of interest as a general model of calcium carbonate biomineralization. Knowledge of proteins and molecular mechanisms in eggshell assembly may also pave the way to manipulation of thickness of the calcified layer or other features. Comparison of eggshell matrix proteomes of different species may contribute to a better understanding of the mineralization process. The recent publication of the quail genome sequence now enables the proteomic analysis of the quail shell matrix and this comparison with those of chicken and turkey.

Results

The quail eggshell proteome comprised 622 identified proteins, 311 of which were shared with chicken and turkey eggshell proteomes. Forty-eight major proteins (iBAQ-derived abundance higher than 0.1 % of total identified proteome) together covered 94 % of total proteome mass. Fifteen of these are also among the most abundant proteins in chicken and turkey eggshell matrix. Only three proteins with a percentage higher than 1.0 % of the total had not previously been identified as eggshell matrix proteins. These were an uncharacterized member of the latexin family, an uncharacterized protease inhibitor containing a Kunitz domain, and gastric intrinsic factor. The most abundant proteins were ovocleidin-116, ovalbumin and ovocalyxin-36 representing approximately 31, 13 and 8 % of the total identified proteome, respectively. The major phosphoproteins were ovocleidin-116 and osteopontin. While osteopontin phosphorylation sites were predominantly conserved between chicken and quail sequences, conservation was less in ovocleidin-116.

Conclusions

Ovocleidin-116 and ovocalyxin-36 are among the most abundant eggshell matrix proteins in all three species of the family Phasianidae analyzed so far, indicating that their presently unknown function is essential for eggshell mineralization. Evidence for other chicken eggshell-specific proteins in quail was inconclusive. Therefore measurement of additional eggshell proteomes, especially from species of different families and preferentially from outside the order Galliformes, will be necessary.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-015-0078-1) contains supplementary material, which is available to authorized users.

The secretory pathway kinases

Protein phosphorylation is a nearly universal post-translation modification involved in a plethora of cellular events. Even though phosphorylation of extracellular proteins had been observed, the identity of the kinases that phosphorylate secreted proteins remained a mystery until only recently. Advances in genome sequencing and genetic studies have paved the way for the discovery of a new class of kinases that localize within the endoplasmic reticulum, Golgi apparatus and the extracellular space. These novel kinases phosphorylate proteins and proteoglycans in the secretory pathway and appear to regulate various extracellular processes. Mutations in these kinases cause human disease, thus underscoring the biological importance of phosphorylation within the secretory pathway. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases.