Phosphorylated proteins and control over apatite nucleation, crystal growth, and inhibition

Simultaneous co-assembly of collagen and glycosaminoglycans to build a biomimetic extracellular matrix for bone regeneration

Glycosaminoglycans (GAGs), also known as shape modules, are considered junctions that help define the shape of collagen matrix and further promote mineralization during osteogenesis. Many attempts have been made to immobilize GAGs on assembled collagen to modify the latter's surface state. However, it remains unclear how GAGs spontaneously identify collagen molecules during fibrillogenesis in vivo. Understanding the relationship between GAGs and collagen from both the bone physiology and materials science perspectives is of fundamental interest. Here, we introduced hyaluronic acid (HA, a main member of GAGs) during collagen self-assembly, in a process called modification cooperating with self-assembly (MCS). The molecular docking and morphological studies revealed that HA can help define collagen monomer deposition and thus promote fibrillogenesis through steric hindrance or by directly forming hydrogen bonds. Meanwhile, HA acts as a templating chaperone (TC) to increase the local mineral concentration within intrafibrillar channels but does not initiate nucleation, thus improving the crystallinity of formed apatite. The scaffolds synthesized through MCS model significantly improved the physicochemical stability and mechanical strength of collagen-based scaffolds. The optimized scaffolds promoted in-situ osteogenesis by stimulating the osteogenic differentiation of bone mesenchymal stem cells, either in an osteogenic medium, or after implantation into critical calvarial defects. This study provides novel insights towards evolving engineering scaffolds from inert supports to functional substitutes.

Hybrid Hydroxyapatite-Metal Complex Materials Derived from Amino Acids and Nucleobases

Calcium phosphates (CaPs) and their substituted derivatives encompass a large number of compounds with a vast presence in nature that have aroused a great interest for decades. In particular, hydroxyapatite (HAp, Ca10(OH)2(PO4)6) is the most abundant CaP mineral and is significant in the biological world, at least in part due to being a major compound in bones and teeth. HAp exhibits excellent properties, such as safety, stability, hardness, biocompatibility, and osteoconductivity, among others. Even some of its drawbacks, such as its fragility, can be redirected thanks to another essential feature: its great versatility. This is based on the compound's tendency to undergo substitutions of its constituent ions and to incorporate or anchor new molecules on its surface and pores. Thus, its affinity for biomolecules makes it an optimal compound for multiple applications, mainly, but not only, in biological and biomedical fields. The present review provides a chemical and structural context to explain the affinity of HAp for biomolecules such as proteins and nucleic acids to generate hybrid materials. A size-dependent criterium of increasing complexity is applied, ranging from amino acids/nucleobases to the corresponding macromolecules. The incorporation of metal ions or metal complexes into these functionalized compounds is also discussed.

Invited review: Modeling milk stability

Novel insights into the stability of milk and milk products during storage and processing result from describing caseins near neutral pH as hydrophilic, intrinsically disordered, proteins. Casein solubility is strongly influenced by pH and multivalent ion binding. Solubility is high at a neutral pH or above, but decreases as the casein net charge approaches zero, allowing a condensed casein phase or gel to form, then increases at lower pH. Of particular importance for casein micelle stability near neutral pH is the proportion of free caseins in the micelle (i.e., caseins not bound directly to nanoclusters of calcium phosphate). Free caseins are more soluble and better able to act as molecular chaperones (to prevent casein and whey protein aggregation) than bound caseins. Some free caseins are highly phosphorylated and can also act as mineral chaperones to inhibit the growth of calcium phosphate phases and prevent mineralized deposits from forming on membranes or heat exchangers. Thus, casein micelle stability is reduced when free caseins bind to amyloid fibrils, destabilized whey proteins or calcium phosphate. The multivalent-binding model of the casein micelle quantitatively describes these and other factors affecting the stability of milk and milk protein products during manufacture and storage.

Advancing dentin remineralization: Exploring amorphous calcium phosphate and its stabilizers in biomimetic approaches

OBJECTIVE

This review elucidates the mechanisms underpinning intrafibrillar mineralization, examines various amorphous calcium phosphate (ACP) stabilizers employed in dentin's intrafibrillar mineralization, and addresses the challenges encountered in clinical applications of ACP-based bioactive materials.

METHODS

The literature search for this review was conducted using three electronic databases: PubMed, Web of Science, and Google Scholar, with specific keywords. Articles were selected based on inclusion and exclusion criteria, allowing for a detailed examination and summary of current research on dentin remineralization facilitated by ACP under the influence of various types of stabilizers.

RESULTS

This review underscores the latest advancements in the role of ACP in promoting dentin remineralization, particularly intrafibrillar mineralization, under the regulation of various stabilizers. These stabilizers predominantly comprise non-collagenous proteins, their analogs, and polymers. Despite the diversity of stabilizers, the mechanisms they employ to enhance intrafibrillar remineralization are found to be interrelated, indicating multiple driving forces behind this process. However, challenges remain in effectively designing clinically viable products using stabilized ACP and maximizing intrafibrillar mineralization with limited materials in practical applications.

SIGNIFICANCE

The role of ACP in remineralization has gained significant attention in dental research, with substantial progress made in the study of dentin biomimetic mineralization. Given ACP's instability without additives, the presence of ACP stabilizers is crucial for achieving in vitro intrafibrillar mineralization. However, there is a lack of comprehensive and exhaustive reviews on ACP bioactive materials under the regulation of stabilizers. A detailed summary of these stabilizers is also instrumental in better understanding the complex process of intrafibrillar mineralization. Compared to traditional remineralization methods, bioactive materials capable of regulating ACP stability and controlling release demonstrate immense potential in enhancing clinical treatment standards.

Role of amelogenin phosphorylation in regulating dental enamel formation

Amelogenin (AMELX), the predominant matrix protein in enamel formation, contains a singular phosphorylation site at Serine 16 (S16) that greatly enhances AMELX's capacity to stabilize amorphous calcium phosphate (ACP) and inhibit its transformation to apatitic enamel crystals. To explore the potential role of AMELX phosphorylation in vivo, we developed a knock-in (KI) mouse model in which AMELX phosphorylation is prevented by substituting S16 with Ala (A). As anticipated, AMELXS16A KI mice displayed a severe phenotype characterized by weak hypoplastic enamel, absence of enamel rods, extensive ectopic calcifications, a greater rate of ACP transformation to apatitic crystals, and progressive cell pathology in enamel-forming cells (ameloblasts). In the present investigation, our focus was on understanding the mechanisms of action of phosphorylated AMELX in amelogenesis. We have hypothesized that the absence of AMELX phosphorylation would result in a loss of controlled mineralization during the secretory stage of amelogenesis, leading to an enhanced rate of enamel mineralization that causes enamel acidification due to excessive proton release. To test these hypotheses, we employed microcomputed tomography (µCT), colorimetric pH assessment, and Fourier Transform Infrared (FTIR) microspectroscopy of apical portions of mandibular incisors from 8-week old wildtype (WT) and KI mice. As hypothesized, µCT analyses demonstrated significantly higher rates of enamel mineral densification in KI mice during the secretory stage compared to the WT. Despite a greater rate of enamel densification, maximal KI enamel thickness increased at a significantly lower rate than that of the WT during the secretory stage of amelogenesis, reaching a thickness in mid-maturation that is approximately half that of the WT. pH assessments revealed a lower pH in secretory enamel in KI compared to WT mice, as hypothesized. FTIR findings further demonstrated that KI enamel is comprised of significantly greater amounts of acid phosphate compared to the WT, consistent with our pH assessments. Furthermore, FTIR microspectroscopy indicated a significantly higher mineral-to-organic ratio in KI enamel, as supported by µCT findings. Collectively, our current findings demonstrate that phosphorylated AMELX plays crucial mechanistic roles in regulating the rate of enamel mineral formation, and in maintaining physico-chemical homeostasis and the enamel growth pattern during early stages of amelogenesis.

STMP and PVPA as Templating Analogs of Noncollagenous Proteins Induce Intrafibrillar Mineralization of Type I Collagen via PCCP Process

The phosphorylated noncollagenous proteins (NCPs) play a vital role in manipulating biomineralization, while the mechanism of phosphorylation of NCPs in intrafibrillar mineralization of collagen fibril has not been completely deciphered. Poly(vinylphosphonic acid) (PVPA) and sodium trimetaphosphate (STMP) as templating analogs of NCPs induce hierarchical mineralization in cooperation with indispensable sequestration analogs such as polyacrylic acid (PAA) via polymer-induced liquid-like precursor (PILP) process. Herein, STMP-Ca and PVPA-Ca complexes are proposed to achieve rapid intrafibrillar mineralization through polyelectrolyte-Ca complexes pre-precursor (PCCP) process. This strategy is further verified effectively for remineralization of demineralized dentin matrix both in vitro and in vivo. Although STMP micromolecule fails to stabilize amorphous calcium phosphate (ACP) precursor, STMP-Ca complexes facilely permeate into intrafibrillar interstices and trigger phase transition of ACP to hydroxyapatite within collagen. In contrast, PVPA-stabilized ACP precursors lack liquid-like characteristic and crystallize outside collagen due to rigid conformation of PVPA macromolecule, while PVPA-Ca complexes infiltrate into partial intrafibrillar intervals under electrostatic attraction and osmotic pressure as evidenced by intuitionistic 3D stochastic optical reconstruction microscopy (3D-STORM). The study not only extends the variety and size range of polyelectrolyte for PCCP process but also sheds light on the role of phosphorylation for NCPs in biomineralization.

Effects of chain lengths and backbone chirality on the bone-targeting ability of poly(glutamic acid)s

Anionic synthetic polypeptides are promising candidates as standalone bone-targeting drug carriers. Nevertheless, the structure-property relationship of the bone-targeting ability of polypeptides remains largely unexplored. Herein we report the optimization of the in vitro and in vivo bone-targeting ability of poly(glutamic acid)s (PGAs) by altering their chain lengths and backbone chirality. PGA 100-mers exhibited higher hydroxyapatite affinity in vitro, but their rapid macrophage clearance limited their targeting ability. Shorter PGA was therefore favored in terms of in vivo bone targeting. Meanwhile, the backbone chirality showed less significant impact on the in vitro and in vivo targeting behavior. This study highlights the modulation of structural parameters on the bone-targeting performance of anionic polypeptides, shedding light on the future design of polypeptide-based carriers.

Dentin matrix protein 1 and HUVEC-ECM scaffold promote the differentiation of human dental pulp stem cells into endothelial lineage: implications in regenerative medicine

Reprograming of the dental pulp somatic cells to endothelial cells is an attractive strategy for generation of new blood vessels. For tissue regeneration, vascularization of engineered constructs is crucial to improve repair mechanisms. In this study, we show that dentin matrix protein 1 (DMP1) and HUVEC-ECM scaffold enhances the differentiation potential of dental pulp stem cells (DPSCs) to an endothelial phenotype. Our results show that the differentiated DPSCs expressed endothelial markers CD31 and VE-Cadherin (CD144) at 7 and 14 days. Expression of CD31 and VE-Cadherin (CD144) were also confirmed by immunofluorescence. Furthermore, flow cytometry analysis revealed a steady increase in CD31 and VE-Cadherin (CD144) positive cells with DMP1 treatment when compared with control. In addition, integrins specific for endothelial cells were highly expressed during the differentiation process. The endothelial cell signature of differentiated DPSCs were additionally characterized for key endothelial cell markers using gene expression by RT-PCR, Western blotting, immunostaining, and RNA-seq analysis. Furthermore, the angiogenic phenotype was confirmed by tubule and capillary sprout formation. Overall, stimulation of DPSCs by DMP1 and use of HUVEC-ECM scaffold promoted their differentiation into phenotypically, transcriptionally, and functionally differentiated bonafide endothelial cells. This study is novel, physiologically relevant and different from conventional strategies.

New Avenues for Capturing Mineralization Events at Biomaterial Interfaces with Liquid-Transmission Electron Microscopy

Liquid-transmission electron microscopy (liquid-TEM) provides exciting potential for capturing mineralization events at biomaterial interfaces, though it is largely unexplored. To address this, we established a unique approach to visualize calcium phosphate (CaP)-titanium (Ti) interfacial mineralization events by combining the nanofabrication of Ti lamellae by focused ion beam with in situ liquid-TEM. Multiphasic CaP particles were observed to nucleate, adhere, and form different assemblies onto and adjacent to Ti lamellae. Here, we discuss new approaches for exploring the interaction between biomaterials and liquids at the nanoscale. Driving this technology is crucial for understanding and controlling biomineralization to improve implant osseointegration and direct new pathways for mineralized tissue disease treatment in the future.

Material-specific binding peptides empower sustainable innovations in plant health, biocatalysis, medicine and microplastic quantification

Material-binding peptides (MBPs) have emerged as a diverse and innovation-enabling class of peptides in applications such as plant-/human health, immobilization of catalysts, bioactive coatings, accelerated polymer degradation and analytics for micro-/nanoplastics quantification. Progress has been fuelled by recent advancements in protein engineering methodologies and advances in computational and analytical methodologies, which allow the design of, for instance, material-specific MBPs with fine-tuned binding strength for numerous demands in material science applications. A genetic or chemical conjugation of second (biological, chemical or physical property-changing) functionality to MBPs empowers the design of advanced (hybrid) materials, bioactive coatings and analytical tools. In this review, we provide a comprehensive overview comprising naturally occurring MBPs and their function in nature, binding properties of short man-made MBPs (<20 amino acids) mainly obtained from phage-display libraries, and medium-sized binding peptides (20-100 amino acids) that have been reported to bind to metals, polymers or other industrially produced materials. The goal of this review is to provide an in-depth understanding of molecular interactions between materials and material-specific binding peptides, and thereby empower the use of MBPs in material science applications. Protein engineering methodologies and selected examples to tailor MBPs toward applications in agriculture with a focus on plant health, biocatalysis, medicine and environmental monitoring serve as examples of the transformative power of MBPs for various industrial applications. An emphasis will be given to MBPs' role in detecting and quantifying microplastics in high throughput, distinguishing microplastics from other environmental particles, and thereby assisting to close an analytical gap in food safety and monitoring of environmental plastic pollution. In essence, this review aims to provide an overview among researchers from diverse disciplines in respect to material-(specific) binding of MBPs, protein engineering methodologies to tailor their properties to application demands, re-engineering for material science applications using MBPs, and thereby inspire researchers to employ MBPs in their research.

Assessment of Physicochemical Characterization and Mineralization of Nanofibrous Scaffold Incorporated With Aspartic Acid for Dental Mineralization: An In Vitro Study

Aim The aim of this study was to assess the physicochemical characterization and mineralization of nanofibrous scaffold incorporated with nanohydroxyapatite (nHA) and aspartic acid (Asp) for dental mineralization.  Methodology Three nanofibrous scaffolds were prepared, namely polycaprolactone (PCL), PCL with nHA, and PCL with nHA and Asp. Each scaffold was prepared separately by electrospinning. The physicochemical characterization of the surface of the nanofibrous scaffold was imaged using a scanning electron microscope (SEM), energy dispersive X-ray Analysis (EDX), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). In vitro mineralization studies were performed by immersing the sample in simulated body fluid (SBF) for 7, 14, and 21 days. The surface of the samples was observed under SEM with EDX. Results SEM analysis of PCL/nHA/Asp revealed that the nanofibers were bead-free, smooth, randomly oriented, and loaded with Asp. The EDX spectra of PCL/nHA/Asp composite nanofibrous scaffold revealed broad peaks and corresponded to the amorphous form, while the sharp peaks corresponded to the specific crystalline structure of nHA. FTIR analysis showed specific functional groups corresponding to PCL, nHA, and Asp. The scaffolds incorporated with Asp exhibited higher mineralization potential with an apatite-like crystal formation, which increased with an increase in the duration of immersion in SBF. Conclusion Physiochemical characterization demonstrated the incorporation of PCL/nHA/Asp in the electrospun nanofibrous scaffold. The mineralization analysis revealed that the presence of Asp enhanced the mineralization when compared with the PCL and PCL/nHA. PCL/nHA/Asp incorporated in scaffold can be a promising material for dental mineralization.

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.

The impact of hydroxyapatite crystal structures and protein interactions on bone's mechanical properties

Hydroxyapatite (HAP) constitutes the primary mineral component of bones, and its crystal structure, along with the surface interaction with proteins, significantly influences the outstanding mechanical properties of bone. This study focuses on natural hydroxyapatite, constructing a surface model with calcium vacancy defects. Employing a representative model of aspartic acid residues, we delve into the adsorption mechanism on the crystal surface and scrutinize the adsorption forms of amino acid residues on HAP and calcium-deficient hydroxyapatite (CDHA) surfaces. The research also explores the impact of different environments on adsorption energy. Furthermore, a simplified sandwich structure of crystal-polypeptide-crystal is presented, analyzing the distribution of amino acid residue adsorption sites on the crystal surface of the polypeptide fragment. This investigation aims to elucidate how the stick-slip mechanism of polypeptide molecules on the crystal surface influences the mechanical properties of the system. By uncovering the interface mechanical behavior between HAP and osteopontin peptides, this article offers valuable theoretical insights for the construction and biomimetic design of biocomposites.

Photo-induced phosphorylation/cyclization of N-homoallyl and N-allyl aldehyde hydrazones to access phosphorylated tetrahydropyridazines and dihydropyrazoles

A photocatalytic radical carbophosphorylation/cyclization of N-homoallyl aldehyde hydrazones with phosphine oxides was developed under metal-free conditions, achieving phosphorylated tetrahydropyridazines in yields up to 95%. Phosphorylated dihydropyrazoles were also constructed, by reacting N-allyl aldehyde hydrazones with phosphine oxides under the same conditions.

Emergence of saliva protein genes in the secretory calcium-binding phosphoprotein (SCPP) locus and accelerated evolution in primates

Genes within the secretory calcium-binding phosphoprotein (SCPP) family evolved in conjunction with major evolutionary milestones: the formation of a calcified skeleton in vertebrates, the emergence of tooth enamel in fish, and the introduction of lactation in mammals. The SCPP gene family also contains genes expressed primarily and abundantly in human saliva. Here, we explored the evolution of the saliva-related SCPP genes by harnessing currently available genomic and transcriptomic resources. Our findings provide insights into the expansion and diversification of SCPP genes, notably identifying previously undocumented convergent gene duplications. In primate genomes, we found additional duplication and diversification events that affected genes coding for proteins secreted in saliva. These saliva-related SCPP genes exhibit signatures of positive selection in the primate lineage while the other genes in the same locus remain conserved. We found that regulatory shifts and gene turnover events facilitated the accelerated gain of salivary expression. Collectively, our results position the SCPP gene family as a hotbed of evolutionary innovation, suggesting the potential role of dietary and pathogenic pressures in the adaptive diversification of the saliva composition in primates, including humans.

Protein-based bioactive coatings: from nanoarchitectonics to applications

Protein-based bioactive coatings have emerged as a versatile and promising strategy for enhancing the performance and biocompatibility of diverse biomedical materials and devices. Through surface modification, these coatings confer novel biofunctional attributes, rendering the material highly bioactive. Their widespread adoption across various domains in recent years underscores their importance. This review systematically elucidates the behavior of protein-based bioactive coatings in organisms and expounds on their underlying mechanisms. Furthermore, it highlights notable advancements in artificial synthesis methodologies and their functional applications in vitro. A focal point is the delineation of assembly strategies employed in crafting protein-based bioactive coatings, which provides a guide for their expansion and sustained implementation. Finally, the current trends, challenges, and future directions of protein-based bioactive coatings are discussed.

Reinforced dentin remineralization via a novel dual-affinity peptide

OBJECTIVES

In light of the constantly flowing saliva, anti-caries remineralization agents are inclined to be taken away. Owing to their limited residence time, the remineralization effect is not as desirable as expected. Hence, our study aimed to synthesize a novel peptide (DGP) with high affinity to both collagen fibrils and hydroxyapatite, and investigated its dentin remineralization efficacy in vitro and anti-caries capability in vivo.

METHODS

DGP was synthesized through Fmoc solid-phase reaction. The binding ability and interaction mechanism of DGP to demineralized dentin were investigated. Dentin specimens were demineralized, then treated with DGP and deionized water respectively. The specimens were incubated in artificial saliva and in-vitro remineralization effectiveness was analyzed after 14 days. The rat caries model was established to further scrutinize the in-vivo efficacy of caries prevention.

RESULTS

DGP possesses an enhanced adhesion force of 12.29 ± 1.12 nN to demineralized dentin. The favorable adsorption capacity is ascribed to the stable hydrogen bonds between S2P-101 and ASP-100 of DGP and GLY33 and PRO-16 of collagen fibers. Abundant mineral deposits and remarkable tubule occlusion were observed in the DGP group. DGP-treated dentin obtained notable microhardness recovery and higher mineral content after a 14-day remineralization regimen. DGP also demonstrated potent caries prevention in vivo, with substantially fewer carious lesions and significantly lower Keyes scoring.

SIGNIFICANCE

DGP proves to possess a high affinity to demineralized dentin regardless of saliva flowing, thus enhancing remineralization potency significantly in vitro and in vivo, potential for dental caries prevention and combatting initial dentin caries clinically.

Protein-guided biomimetic nanomaterials: a versatile theranostic nanoplatform for biomedical applications

Over the years, bioinspired mineralization-based approaches have been applied to synthesize multifunctional organic-inorganic nanocomposites. These nanocomposites can address the growing demands of modern biomedical applications. Proteins, serving as vital biological templates, play a pivotal role in the nucleation and growth processes of various organic-inorganic nanocomposites. Protein-mineralized nanomaterials (PMNMs) have attracted significant interest from researchers due to their facile and convenient preparation, strong physiological activity, stability, impressive biocompatibility, and biodegradability. Nevertheless, few comprehensive reviews have expounded on the progress of these nanomaterials in biomedicine. This article systematically reviews the principles and strategies for constructing nanomaterials using protein-directed biomineralization and biomimetic mineralization techniques. Subsequently, we focus on their recent applications in the biomedical field, encompassing areas such as bioimaging, as well as anti-tumor, anti-bacterial, and anti-inflammatory therapies. Furthermore, we discuss the challenges encountered in practical applications of these materials and explore their potential in future applications. This review aspired to catalyze the continued development of these bioinspired nanomaterials in drug development and clinical diagnosis, ultimately contributing to the fields of precision medicine and translational medicine.

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.

Nucleation Domains in Biomineralization: Biomolecular Sequence and Conformational Features

Biomolecules play a vital role in the regulation of biomineralization. However, the characteristics of practical nucleation domains are still sketchy. Herein, the effects of the representative biomolecular sequence and conformations on calcium phosphate (Ca-P) nucleation and mineralization are investigated. The results of computer simulations and experiments prove that the line in the arrangement of dual acidic/essential amino acids with a single interval (Bc (Basic) -N (Neutral) -Bc-N-Ac (Acidic)- NN-Ac-N) is most conducive to the nucleation. 2α-helix conformation can best induce Ca-P ion cluster formation and nucleation. "Ac- × × × -Bc" sequences with α-helix are found to be the features of efficient nucleation domains, in which process, molecular recognition plays a non-negligible role. It further indicates that the sequence determines the potential of nucleation/mineralization of biomolecules, and conformation determines the ability of that during functional execution. The findings will guide the synthesis of biomimetic mineralized materials with improved performance for bone repair.

Occlusive membranes for guided regeneration of inflamed tissue defects

Guided bone regeneration aided by the application of occlusive membranes is a promising therapy for diverse inflammatory periodontal diseases. Symbiosis, homeostasis between the host microbiome and cells, occurs in the oral environment under normal, but not pathologic, conditions. Here, we develop a symbiotically integrating occlusive membrane by mimicking the tooth enamel growth or multiple nucleation biomineralization processes. We perform human saliva and in vivo canine experiments to confirm that the symbiotically integrating occlusive membrane induces a symbiotic healing environment. Moreover, we show that the membrane exhibits tractability and enzymatic stability, maintaining the healing space during the entire guided bone regeneration therapy period. We apply the symbiotically integrating occlusive membrane to treat inflammatory-challenged cases in vivo, namely, the open and closed healing of canine premolars with severe periodontitis. We find that the membrane promotes symbiosis, prevents negative inflammatory responses, and improves cellular integration. Finally, we show that guided bone regeneration therapy with the symbiotically integrating occlusive membrane achieves fast healing of gingival soft tissue and alveolar bone.

Copper(II)-catalyzed cascade Csp2-P/C-C bond formation to construct benzo[d]thiazol-2-ylphosphonates

A novel, copper(II)-catalyzed cascade Csp2-P/C-C bond formation in o-haloaryl isothiocyanates with organophosphorus esters has been developed under mild conditions. A series of benzo[d]thiazol-2-ylphosphonates were synthesized in moderate to good yields. Different from the traditional method of obtaining these scaffolds with radical reactions, the method proposed allows accessing them via ionic reactions and has the advantages of easy access to raw materials and simple operation. Finally, we carried out a gram-scale experiment to further demonstrate the scalability of this strategy in the efficient synthesis of benzo[d]thiazol-2-ylphosphonates.

Biomimetic Mineralization: From Microscopic to Macroscopic Materials and Their Biomedical Applications

Biomineralization is an attractive pathway to produce mineral-based biomaterials with high performance and hierarchical structures. To date, the biomineralization process and mechanism have been extensively studied, especially for the formation of bone, teeth, and nacre. Inspired by those, abundant biomimetic mineralized materials have been fabricated for biomedical applications. Those bioinspired materials generally exhibit great mechanical properties and biological functions. Nevertheless, substantial gaps remain between biomimetic materials and natural materials, particularly with respect to mechanical properties and mutiscale structures. This Review summarizes the recent progress of micro- and macroscopic biomimetic mineralization from the perspective of materials synthesis and biomedical applications. To begin with, we discuss the progress of biomimetic mineralization at the microscopic level. The mechanical strength, stability, and functionality of the nano- and micromaterials are significantly improved by introducing biominerals, such as DNA nanostructures, nanovaccines, and living cells. Next, numerous biomimetic strategies based on biomineralization at the macroscopic scale are highlighted, including in situ mineralization and bottom-up assembly of mineralized building blocks. Finally, challenges and future perspectives regarding the development of biomimetic mineralization are also presented with the aim of offering insights for the rational design and fabrication of next-generation biomimetic mineralized materials.

Hierarchical Assembly of Intrinsically Disordered Short Peptides

The understanding on how short peptide assemblies transit from disorder to order remains limited due to the lack of atomistic structures. Here we report cryo-EM structure of the nanofibers short intrinsically disordered peptides (IDPs). Upon lowering pH or adding calcium ions, the IDP transitions from individual nanoparticles to nanofibers containing an aromatic core and a disordered periphery comprised of 2 to 5 amino acids. Protonating the phosphate or adding more metal ions further assembles the nanofibers into filament bundles. The assemblies of the IDP analogs with controlled chemistry, such as phosphorylation site, hydrophobic interactions, and sequences indicate that metal ions interact with the flexible periphery of the nanoparticles of the IDPs to form fibrils and enhance the interfibrillar interactions to form filament bundles. Illustrating that an IDP self-assembles from disorder to order, this work offers atomistic molecular insights to understand assemblies of short peptides driven by noncovalent interactions.

Relevant Properties and Potential Applications of Sericin in Bone Regeneration

The potential of sericin, a protein derived from silkworms, is explored in bone graft applications. Sericin's biocompatibility, hydrophilic nature, and cost-effectiveness make it a promising candidate for enhancing traditional graft materials. Its antioxidant, anti-inflammatory, and UV-resistant properties contribute to a healthier bone-healing environment, and its incorporation into 3D-printed grafts could lead to personalized medical solutions. However, despite these promising attributes, there are still gaps in our understanding. The precise mechanism through which sericin influences bone cell growth and healing is not fully understood, and more comprehensive clinical trials are needed to confirm its long-term biocompatibility in humans. Furthermore, the best methods for incorporating sericin into existing graft materials are still under investigation, and potential allergic reactions or immune responses to sericin need further study.

Four-layer folding framework: design, GAP synthesis, and aggregation-induced emission

The design and synthesis of a type of [1 + 4 + 2] four-layer framework have been conducted by taking advantage of Suzuki-Miyaura cross-coupling and group-assisted purification (GAP) chemistry. The optimized coupling of double-layer diboronic esters with 1-bromo-naphth-2-yl phosphine oxides resulted in a series of multilayer folding targets, showing a broad scope of substrates and moderate to excellent yields. The final products were purified using group-assisted purification chemistry/technology, achieved simply by washing crude products with 95% EtOH without the use of chromatography and recrystallization. The structures were fully characterized and assigned by performing X-ray crystallographic analysis. UV-vis absorption, photoluminescence (PL), and aggregation-induced emission (AIE) were studied for the resulting multilayer folding products.

Fam20C overexpression in odontoblasts regulates dentin formation and odontoblast differentiation

FAM20C phosphorylates secretory proteins at S-x-E/pS motifs, and previous studies of Fam20C-dificient mice revealed that FAM20C played essential roles in bone and tooth formation. Inactivation of FAM20C in mice led to hypophosphatemia that masks direct effect of FAM20C in these tissues, and consequently the direct role of FAM20C remains unknown. Our previous study reported that osteoblast/odontoblast-specific Fam20C transgenic (Fam20C-Tg) mice had normal serum phosphate levels and that osteoblastic FAM20C-mediated phosphorylation regulated bone formation and resorption. Here, we investigated the direct role of FAM20C in dentin using Fam20C-Tg mice. The tooth of Fam20C-Tg mice contained numerous highly phosphorylated proteins, including SIBLINGs, compared to that of wild-type mice. In Fam20C-Tg mice, coronal dentin volume decreased and mineral density unchanged at early age, while the volume unchanged and the mineral density elevated at maturity. In these mice, radicular dentin volume and mineral density decreased at all ages, and histologically, the radicular dentin had wider predentin and abnormal apical-side dentin with embedded cells and argyrophilic canaliculi. Immunohistochemical analyses revealed that abnormal apical-side dentin had bone and dentin matrix properties accompanied with osteoblast-lineage cells. Further, in Fam20C-Tg mice, DSPP content which is important for dentin formation, was reduced in dentin, especially radicular dentin, which might lead to defects mainly in radicular dentin. Renal subcapsular transplantations of tooth germ revealed that newly formed radicular dentin replicated apical abnormal dentin of Fam20C-Tg mice, corroborating that FAM20C overexpression indeed caused the abnormal dentin. Our findings indicate that odontoblastic FAM20C-mediated phosphorylation in the tooth regulates dentin formation and odontoblast differentiation.

Self-assembled peptide P11-4 interacts with the type I collagen C-terminal telopeptide domain and calcium ions

OBJECTIVES

Evaluate molecularly the role of P11-4 self-assembly peptide in dentin remineralization and its interaction with collagen I.

METHODS

The calcium-responsive P11-4 peptide was analyzed by intrinsic fluorescence emission spectrum, circular dichroism spectrum (CD), and atomic force microscope (AFM). Differential light scattering was used to monitor the nucleation growth rate of calcium phosphate nanocrystals in the absence or in the presence of P11-4. AFM was used to analyze the radial size (nm) of calcium phosphate nanocrystals formed in the absence or in the presence of P11-4, as well as to verify the spatial structure of P11-4 in the absence or in the presence of Ca2+.

RESULTS

The interaction of Ca2+ with the P11-4 (KD = 0.58 ± 0.06 mM) promotes the formation of β-sheet antiparallel structure, leads to its precipitation in saturated solutions of Ca/P = 1.67 and induces the formation of parallel large fibrils (0.6 - 1.5 µm). P11-4 organized the HAP nucleation by reducing both the growth rate and size variability of nanocrystals, analyzed by the F test (p < 0.0001, N = 30). P11-4 interacts (KD = 0.75 ± 0.06 μM) with the KGHRGFSGL motif present at the C-terminal collagen telopeptide domain. P11-4 also increased the amount of HAP and collagen in the MDPC-23 cells.

SIGNIFICANCE

The presented data propose a mechanism that will help future clinical and/or basic research to better understand a molecule able to inhibit structural collagen loss and help the impaired tissue to remineralize.

Formation of Hydroxyapatite-Based Hybrid Materials in the Presence of Platelet-Poor Plasma Additive

Biomaterials based on hydroxyapatite with controllable composition and properties are promising in the field of regenerative bone replacement. One approach to regulate the phase composition of the materials is the introduction of biopolymer-based additives into the synthesis process. The purpose of present study was to investigate the formation of hydroxyapatite-based hybrid materials in the presence of 6-24% platelet-poor plasma (PPP) additive, at a [Ca2+]/[PO43-] ratio of 1.67, pH 11, and varying maturing time from 4 to 9 days. The mineral component of the materials comprised 53% hydroxyapatite/47% amorphous calcium phosphate after 4 days of maturation and 100% hydroxyapatite after 9 days of maturation. Varying the PPP content between 6% and 24% brought about the formation of materials with rather defined contents of amorphous calcium phosphate and biopolymer component and the desired morphology, ranging from typical apatitic conglomerates to hybrid apatite-biopolymer fibers. The co-precipitated hybrid materials based on hydroxyapatite, amorphous calcium phosphate, and PPP additive exhibited increased solubility in SBF solution, which defines their applicability for repairing rhinoplastic defects.

Tandem addition of nucleophilic and electrophilic reagents to vinyl phosphinates: the stereoselective formation of organophosphorus compounds with congested tertiary carbons

Carbon anions formed via the addition of Grignard reagents to SP-vinyl phosphinates were modified with electrophilic reagents to afford organophosphorus compounds with diverse carbon skeletons. The electrophiles included acids, aldehydes, epoxy groups, chalcogens and alkyl halides. When alkyl halides were used, bis-alkylated products were afforded. Substitution reactions or polymerization occurred when the reaction was applied to vinyl phosphine oxides.

Remineralization of Dentinal Lesions Using Biomimetic Agents: A Systematic Review and Meta-Analysis

The objective of this article was to systematically provide an up-to-date review on the different methods of remineralizing human dentine using different biomimetic agents. The authors performed a systematic search within PubMed, Scopus, and Web of Science in addition to the grey literature in Google Scholar^® using MeSH terms. The PICO question was P: human teeth dentinal sections; I: application of biomimetic remineralizing agents; C: other non-biomimetic approaches; O: extent of remineralization and physical properties of remineralized dentine. The initially identified studies were screened for titles and abstracts. Non-English articles, reviews, animal studies, studies involving the resin-dentine interface, and other irrelevant articles were then excluded. The other remaining full-text articles were retrieved. Bibliographies of the remaining articles were searched for relevant studies that could be included. A total of 4741 articles were found, and finally, 39 full-text articles were incorporated in the current systematic review. From these, twenty-six research studies used non-collagenous protein (NCP) analogs to biomineralize dentine, six studies used bioactive materials derived from natural sources, six studies used zinc hydroxyapatite, and one study used amelogenin peptide to induce hydroxyapatite formation on the surface of demineralized dentine. Additive effects of triclosan and epigenin were assessed when combined with commonly available NCPs. Overall, a moderate risk of bias was observed and, hence, the findings of the included studies could be acceptable. A meta-analysis of some similar studies was performed to assess the depth of remineralization and elastic modulus. Despite having high heterogeneity (I² > 90), all the studies showed a significant improvement in biomimetic remineralization efficacy as compared to the control. All the included studies carried out a functional remineralization assessment and found a 90-98% efficacy in the extent of remineralization while the elastic modulus reached 88.78 ± 8.35 GPa, which is close to natural dentine. It is pertinent to note the limitations of these studies that have been carried out in vitro under controlled settings, which lack the effects of a natural oral environment. To conclude, the authors suggest that the biomimetic remineralization of dentine using NCP analogs, bioactive materials, and natural products carries significant potential in treating dentinal lesions; however, more long-term studies are needed to assess their clinical applications in vivo.

Mineralogy, geochemistry, and micromorphology of human kidney stones (urolithiasis) from Mersin, the southern Turkey

This study describes the primary characteristics of the selected kidney stones surgically removed from the patients at the Mersin University Hospital in the southern Turkey and interprets their formation via petrographic, geochemical, XRD, SEM-EDX, and ICP-MS/OES analyses. The analytical results revealed that the kidney stones are composed of the minerals whewellite, struvite, hydroxyapatite, and uric acid alone or in different combinations. The samples occur in staghorn, bean-shaped composite, and individual rounded particle shapes, which are controlled by the shape of the nucleus and the site of stone formation. The cross-section of the samples shows concentric growth layers due to variations in saturation, characterizing the metastable phase. Kidney stone formation includes two main stages: (i) nucleation and (ii) aggregation and/or growth. Nucleation was either Randall plaque of hydroxyapatite in tissue on the surface of the papilla or a coating of whewellite on the plaque, or crystallization as free particles in the urine. Subsequently, aggregation or growth occurs by precipitation of stone-forming materials around the plaque or coating carried into the urine, or around the nucleus formed in situ in the urine. Urinary supersaturation is the main driving force of crystallization processes; and is controlled by many factors including bacterially induced supersaturation.

Periodontal regeneration: Lessons from the periodontal ligament-cementum junction in diverse animal models

The attachment of the roots of mammalian teeth of limited eruption to the jawbone is reliant in part on the mineralization of collagen fibrils of the periodontal ligament (PDL) at their entry into bone and cementum as Sharpey's fibers. In periodontitis, a high prevalence infection of periodontal tissues, the attachment apparatus of PDL to the tooth root is progressively destroyed. Despite the pervasiveness of periodontitis and its attendant health care costs, and regardless of decades of research into various possible treatments, reliable restoration of periodontal attachment after surgery is not achievable. Notably, treatment outcomes in animal studies have often demonstrated more positive regenerative outcomes than human clinical studies. Conceivably, defining how species diversity affects cementogenesis and cementum/PDL regeneration could be instructive for informing novel and more efficacious treatment strategies. Here we briefly review differences in cementum and PDL attachment in commonly used animal models to consider how species differences may lead to enhanced regenerative outcomes.

Insights into the Structure and Function of TRIP-1, a Newly Identified Member in Calcified Tissues

Eukaryotic initiation factor subunit I (EIF3i), also called as p36 or TRIP-1, is a component of the translation initiation complex and acts as a modulator of TGF-β signaling. We demonstrated earlier that this intracellular protein is not only exported to the extracellular matrix via exosomes but also binds calcium phosphate and promotes hydroxyapatite nucleation. To assess other functional roles of TRIP-1, we first examined their phylogeny and showed that it is highly conserved in eukaryotes. Comparing human EIF3i sequence with that of 63 other eukaryotic species showed that more than 50% of its sequence is conserved, suggesting the preservation of its important functional role (translation initiation) during evolution. TRIP-1 contains WD40 domains and predicting its function based on this structural motif is difficult as it is present in a vast array of proteins with a wide variety of functions. Therefore, bioinformatics analysis was performed to identify putative regulatory functions for TRIP-1 by examining the structural domains and post-translational modifications and establishing an interactive network using known interacting partners such as type I collagen. Insight into the function of TRIP-1 was also determined by examining structurally similar proteins such as Wdr5 and GPSß, which contain a ß-propeller structure which has been implicated in the calcification process. Further, proteomic analysis of matrix vesicles isolated from TRIP-1-overexpressing preosteoblastic MC3T3-E1 cells demonstrated the expression of several key biomineralization-related proteins, thereby confirming its role in the calcification process. Finally, we demonstrated that the proteomic signature in TRIP1-OE MVs facilitated osteogenic differentiation of stem cells. Overall, we demonstrated by bioinformatics that TRIP-1 has a unique structure and proteomic analysis suggested that the unique osteogenic cargo within the matrix vesicles facilitates matrix mineralization.

Nickel-Catalyzed Radical Ring-Opening Phosphorylation of Cycloalkyl Hydroperoxides Leading to Distal Acylphosphine Oxides

A facile and efficient nickel-catalyzed C-C bond cleavage/phosphorylation of various cycloalkyl hydroperoxides was developed. This radical ring-opening strategy provided practical access to structurally diverse distal ketophosphine oxides in one pot through concurrent C═O/C-P bond formation with high atom economy under mild room temperature and base-free conditions.

Regiodivergent Metal-Controlled Synthesis of Multiply Substituted Quinolin-2-yl- and Quinolin-3-ylphosphonates

In this study, we developed a selective method for synthesis of multi-substituted quinoline-2-ylphosphonates and quinoline-3-ylphosphonates by copper- or gold-catalyzed reactions of phosphoryl-substituted conjugated ynones with 2'-amino-2,2,2-trifluoroacetophenones. The approach proposed makes it possible to obtain various substituted quinolines in good yields. It is also shown that (4,4,4-trifluoro-3-oxobut-1-yn-1-yl)phosphonate reacts with 2-aminoaryl ketones under non-catalytic conditions with formation of 4-substituted quinoline-2-ylphosphonates in high yields.

Important roles of odontoblast membrane phospholipids in early dentin mineralization

The objective of this study was to first identify the timing and location of early mineralization of mouse first molar, and subsequently, to characterize the nucleation site for mineral formation in dentin from a materials science viewpoint and evaluate the effect of environmental cues (pH) affecting early dentin formation. Early dentin mineralization in mouse first molars began in the buccal central cusp on post-natal day 0 (P0), and was first hypothesized to involve collagen fibers. However, elemental mapping indicated the co-localization of phospholipids with collagen fibers in the early mineralization area. Co-localization of phosphatidylserine and annexin V, a functional protein that binds to plasma membrane phospholipids, indicated that phospholipids in the pre-dentin matrix were derived from the plasma membrane. A 3-dimensional in vitro biomimetic mineralization assay confirmed that phospholipids from the plasma membrane are critical factors initiating mineralization. Additionally, the direct measurement of the tooth germ pH, indicated it to be alkaline. The alkaline environment markedly enhanced the mineralization of cell membrane phospholipids. These results indicate that cell membrane phospholipids are nucleation sites for mineral formation, and could be important materials for bottom-up approaches aiming for rapid and more complex fabrication of dentin-like structures.

Interactions between Dental MSCs and Biomimetic Composite Scaffold during Bone Remodeling Followed by In Vivo Real-Time Bioimaging

Oral-maxillofacial tumor removal can generate critical bone defects and major problems for patients, causing dysfunctionalities and affecting oral competencies such as mastication, swallowing, and breathing. The association of novel biomaterials and cell therapies in tissue engineering strategies could offer new strategies to promote osteomucosa healing. This study focused on the development of a bioengineered construct loaded with human dental follicle cells (MSCs). To increase the bioconstruct integration to the surrounding tissue, a novel and comprehensive approach was designed combining an injectable biomimetic hydrogel and dental stem cells (hDFMSCs) expressing luminescence/fluorescence for semi-quantitative tissue imaging in live animals. This in vivo model with human MSCs was based on an intramembranous bone regeneration process (IMO). Biologically, the biocomposite based on collagen/nanohydroxyapatite filled with cell-loaded osteopontin-fibrin hydrogel (Coll/nanoHA OPN-Fb) exhibited a high cellular proliferation rate, increased bone extracellular matrix deposition (osteopontin) and high ALP activity, indicating an early osteogenic differentiation. Thus, the presence of human OPN enhanced hDFMSC adhesion, migration, and spatial distribution within the 3D matrix. The developed 3D bioconstruct provided the necessary pro-regenerative effect to modulate the biological response, precisely fitting the bone defect with fine-tuned adjustment to the surrounding original structure and promoting oral osteomucosa tissue regeneration. We were also able to track the cells in vivo and evaluate their behavior (migration, proliferation, and differentiation), providing a glimpse into bone regeneration and helping in the optimization of patient-specific therapies.

Advances in biomimetic collagen mineralisation and future approaches to bone tissue engineering

With an ageing world population and ~20% of adults in Europe being affected by bone diseases, there is an urgent need to develop advanced regenerative approaches and biomaterials capable to facilitate tissue regeneration while providing an adequate microenvironment for cells to thrive. As the main components of bone are collagen and apatite mineral, scientists in the tissue engineering field have attempted in combining these materials by using different biomimetic approaches to favour bone repair. Still, an ideal bone analogue capable of mimicking the distinct properties (i.e., mechanical properties, degradation rate, porosity, etc.) of cancellous bone is to be developed. This review seeks to sum up the current understanding of bone tissue mineralisation and structure while providing a critical outlook on the existing biomimetic strategies of mineralising collagen for bone tissue engineering applications, highlighting where gaps in knowledge exist.

Changes in the C-terminal, N-terminal, and histidine regions of amelogenin reveal the role of oligomer quaternary structure on adsorption and hydroxyapatite mineralization

Adsorption interactions between amelogenin and calcium phosphate minerals are believed to be important to amelogenin's function in enamel formation, however, the role of specific amino acid residues and domains within the protein in controlling adsorption is not well known. We synthesized "mechanistic probes" by systematically removing charged regions of amelogenin in order to elucidate their roles. The probes included amelogenin without the charged residues in the N-terminus (SEKR), without two, three, or eight histidines (H) in the central protein region (H2, H3, H8), or without the C-terminal residues (Delta). In-situ atomic force microscopy (AFM) adsorption studies onto hydroxyapatite (HAP) single crystals confirmed that the C-terminus was the dominant domain in promoting adsorption. We propose that subtle changes in protein-protein interactions for proteins with histidines and N-terminal residues removed resulted in changes in the oligomer quaternary size and structure that also affected protein adsorption. HAP mineralization studies revealed that the oligomer-HAP binding energy and protein layer thickness were factors in controlling the amorphous calcium phosphate (ACP) to HAP induction time. Our studies with mechanistic probes reveal the importance of the oligomer quaternary structure in controlling amelogenin adsorption and HAP mineralization.

Visible-Light-Promoted Phosphorylation/Cyclization of 1-Acryloyl-2-cyanoindoles in Green Solvent

A visible-light-induced persulfate-promoted cascade phosphorylation/cyclization reaction to access various phosphorylated pyrrolo[1,2-a]indolediones under mild conditions was developed. Notably, the transformation was carried out with diethyl carbonate/H₂O as a green medium at room temperature. More impressively, traditional metal catalysts and photocatalysts could be effectively avoided. The reactions are simple to operate, easy to scale up, and have good functional group tolerance.

Nuclear Magnetic Resonance and Metadynamics Simulations Reveal the Atomistic Binding of l-Serine and O-Phospho-l-Serine at Disordered Calcium Phosphate Surfaces of Biocements

Interactions between biomolecules and structurally disordered calcium phosphate (CaP) surfaces are crucial for the regulation of bone mineralization by noncollagenous proteins, the organization of complexes of casein and amorphous calcium phosphate (ACP) in milk, as well as for structure-function relationships of hybrid organic/inorganic interfaces in biomaterials. By a combination of advanced solid-state NMR experiments and metadynamics simulations, we examine the detailed binding of O-phospho-l-serine (Pser) and l-serine (Ser) with ACP in bone-adhesive CaP cements, whose capacity of gluing fractured bone together stems from the close integration of the organic molecules with ACP over a subnanometer scale. The proximity of each carboxy, aliphatic, and amino group of Pser/Ser to the Ca²⁺ and phosphate species of ACP observed from the metadynamics-derived models agreed well with results from heteronuclear solid-state NMR experiments that are sensitive to the ¹³C-³¹P and ¹⁵N-³¹P distances. The inorganic/organic contacts in Pser-doped cements are also contrasted with experimental and modeled data on the Pser binding at nanocrystalline HA particles grown from a Pser-bearing aqueous solution. The molecular adsorption is driven mainly by electrostatic interactions between the negatively charged carboxy/phosphate groups and Ca²⁺ cations of ACP, along with H bonds to either protonated or nonprotonated inorganic phosphate groups. The Pser and Ser molecules anchor at their phosphate/amino and carboxy/amino moieties, respectively, leading to an extended molecular conformation across the surface, as opposed to an "upright standing" molecule that would result from the binding of one sole functional group.

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.

Biomineralization of bone tissue: calcium phosphate-based inorganics in collagen fibrillar organic matrices

BACKGROUND

Bone regeneration research is currently ongoing in the scientific community. Materials approved for clinical use, and applied to patients, have been developed and produced. However, rather than directly affecting bone regeneration, these materials support bone induction, which regenerates bone. Therefore, the research community is still researching bone tissue regeneration. In the papers published so far, it is hard to find an improvement in the theory of bone regeneration. This review discusses the relationship between the existing theories on hard tissue growth and regeneration and the biomaterials developed so far for this purpose and future research directions.

MAINBODY

Highly complex nucleation and crystallization in hard tissue involves the coordinated action of ions and/or molecules that can produce different organic and inorganic composite biomaterials. In addition, the healing of bone defects is also affected by the dynamic conditions of ions and nutrients in the bone regeneration process. Inorganics in the human body, especially calcium- and/or phosphorus-based materials, play an important role in hard tissues. Inorganic crystal growth is important for treating or remodeling the bone matrix. Biomaterials used in bone tissue regeneration require expertise in various fields of the scientific community. Chemical knowledge is indispensable for interpreting the relationship between biological factors and their formation. In addition, sources of energy for the nucleation and crystallization processes of such chemical bonds and minerals that make up the bone tissue must be considered. However, the exact mechanism for this process has not yet been elucidated. Therefore, a convergence of broader scientific fields such as chemistry, materials, and biology is urgently needed to induce a distinct bone tissue regeneration mechanism.

CONCLUSION

This review provides an overview of calcium- and/or phosphorus-based inorganic properties and processes combined with organics that can be regarded as matrices of these minerals, namely collagen molecules and collagen fibrils. Furthermore, we discuss how this strategy can be applied to future bone tissue regenerative medicine in combination with other academic perspectives.

Promoting effect of a calcium-responsive self-assembly β-sheet peptide on collagen intrafibrillar mineralization

Recently, a de novo synthetic calcium-responsive self-assembly β-sheet peptide ID8 (Ile-Asp-Ile-Asp-Ile-Asp-Ile-Asp) has been developed to serve as the template inducing hydroxyapatite nucleation. The aim of this study was to evaluate the effect of ID8 on intrafibrillar mineralization of collagen making full use of its self-assembly ability. The mineralization experiments were carried out in vitro on both bare Type I collagen and fully demineralized dentin samples. The calcium-responsive self-assembly of ID8 was revealed by circular dichroism spectrum, 8-anilino-1-naphthalenesulfonic acid ammonium salt hydrate assay, attenuated total reflection Fourier transform infrared spectrum (ATR-FTIR) and transmission electron microscope (TEM). Polyacrylic acid (450 kDa) with a concentration of 100 μg ml⁻¹ was selected as the nucleation inhibitor based on the determination of turbidimetry and TEM with selected area electron diffraction (TEM-SAED). The results showed that collagen intrafibrillar mineralization was significantly promoted with the pretreatment of self-assembly ID8 detected by TEM-SAED, SEM, X-ray diffraction and ATR-FTIR. The pretreatment of collagen utilizing self-assembly ID8 not only enhanced intermolecular hydrogen bonding but also contributed to calcium retention inside collagen and significantly increased the hydrophilicity of collagen. These results indicated that peptides with self-assembly properties like ID8 are expected to be potential tools for biomimetic mineralization of collagen.

Between a rock and a hard place: Regulation of mineralization in the periodontium

The periodontium supports and attaches teeth via mineralized and nonmineralized tissues. It consists of two, unique mineralized tissues, cementum and alveolar bone. In between these tissues, lies an unmineralized, fibrous periodontal ligament (PDL), which distributes occlusal forces, nourishes and invests teeth, and harbors progenitor cells for dentoalveolar repair. Many unanswered questions remain regarding periodontal biology. This review will focus on recent research providing insights into one enduring mystery: the precise regulation of the hard-soft tissue borders in the periodontium which define the interfaces of the cementum-PDL-alveolar bone structure. We will focus on advances in understanding the molecular mechanisms that maintain the unmineralized PDL "between a rock and a hard place" by regulating the mineralization of cementum and alveolar bone.