Bones and teeth are biocomposites that require controlled mineral deposition during their self-assembly to form tissues with unique mechanical properties. Acidic extracellular matrix proteins play a pivotal role during biomineral formation. However, the mechanisms of protein-mediated mineral initiation are far from understood. Here we report that dentin matrix protein 1 (DMP1), an acidic protein, can nucleate the formation of hydroxyapatite in vitro in a multistep process that begins by DMP1 binding calcium ions and initiating mineral deposition. The nucleated amorphous calcium phosphate precipitates ripen and nanocrystals form. Subsequently, these expand and coalesce into microscale crystals elongated in the c-axis direction. Characterization of the functional domains in DMP1 demonstrated that intermolecular assembly of acidic clusters into a beta-sheet template was essential for the observed mineral nucleation. Protein-mediated initiation of nanocrystals, as discussed here, might provide a new methodology for constructing nanoscale composites by self-assembly of polypeptides with tailor-made peptide sequences.

Heterogeneous interfaces that are ubiquitous in optoelectronic devices play a key role in the device performance and have led to the prosperity of today’s microelectronics. Interface engineering provides an effective and promising approach to enhancing the device performance of organic field-effect transistors (OFETs) and even developing new functions. In fact, researchers from different disciplines have devoted considerable attention to this concept, which has started to evolve from simple improvement of the device performance to sophisticated construction of novel functionalities, indicating great potential for further applications in broad areas ranging from integrated circuits and energy conversion to catalysis and chemical/biological sensors. In this review article, we provide a timely and comprehensive overview of current efficient approaches developed for building various delicate functional interfaces in OFETs, including interfaces within the semiconductor layers, semiconductor/electrode interfaces, semiconductor/dielectric interfaces, and semiconductor/environment interfaces. We also highlight the major contributions and new concepts of integrating molecular functionalities into electrical circuits, which have been neglected in most previous reviews. This review will provide a fundamental understanding of the interplay between the molecular structure, assembly, and emergent functions at the molecular level and consequently offer novel insights into designing a new generation of multifunctional integrated circuits and sensors toward practical applications.

During bone and dentin mineralization, the crystal nucleation and growth processes are considered to be matrix regulated. Osteoblasts and odontoblasts synthesize a polymeric collagenous matrix, which forms a template for apatite initiation and elongation. Coordinated and controlled reaction between type I collagen and bone/dentin-specific noncollagenous proteins are necessary for well defined biogenic crystal formation. However, the process by which collagen surfaces become mineralized is not understood. Dentin matrix protein 1 (DMP1) is an acidic noncollagenous protein expressed during the initial stages of mineralized matrix formation in bone and dentin. Here we show that DMP1 bound specifically to type I collagen, with the binding region located at the N-telopeptide region of type I collagen. Peptide mapping identified two acidic clusters in DMP1 responsible for interacting with type I collagen. The collagen binding property of these domains was further confirmed by site-directed mutagenesis. Transmission electron microscopy analyses have localized DMP1 in the gap region of the collagen fibrils. Fibrillogenesis assays further demonstrated that DMP1 accelerated the assembly of the collagen fibrils in vitro and also increased the diameter of the reconstituted collagen fibrils. In vitro mineralization studies in the presence of calcium and phosphate ions demonstrated apatite deposition only at the collagenbound DMP1 sites. Thus specific binding of DMP1 and possibly other noncollagenous proteins on the collagen fibril might be a key step in collagen matrix organization and mineralization.Mineralized tissues such as bone and dentin are hierarchically organized biocomposites possessing unique mechanical properties (1). Understanding the biomineralization process is of great value for synthesis of bioengineered bone and dentinlike materials with optimum structural properties. Type I collagen accounts for 90% of the total protein in the organic matrix of bone and dentin (1). It not only provides the structural framework with viscoelastic properties but also defines compartments for ordered mineral deposition. Studies have demonstrated that the apatite crystals are first nucleated in the gap region, and the growing mineral platelets are highly organized in a staggered manner within the collagen fibrils (2, 3).It is well established that type I collagen matrix does not have the capacity to induce matrix-specific mineral formation from metastable calcium phosphate solutions that do not spontaneously precipitate. Several in vitro studies have demonstrated that ordered mineralization of apatite on collagen fibril is impossible without additives (4, 5). As a result, much attention has been drawn to the noncollagenous proteins (NCPs) 1 that are tightly bound to the collagen fibers in mineralized tissues. Bone and/or dentin-specific NCPs are mostly acidic in nature and are rich in glutamic acid, aspartic acid, and phosphoserines (6, 7). They possess high calcium binding capacity and hydroxyapatite affinity (8 -10). In vitro ...

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Phosphoproteins of the organic matrix of bone and dentin have been implicated as regulators of the nucleation and growth of the inorganic Ca-P crystals of vertebrate bones and teeth. One such protein identified in the dentin matrix is phosphophoryn (PP). It is highly acidic in nature because of a high content of aspartic acid and phosphate groups on serines. The 244-residue carboxyl-terminal domain of rat PP, predominantly containing the aspartic acid-serine repeats, has been cloned, and the corresponding protein has been expressed recombinantly in Escherichia coli. This portion of PP, named DMP2 (dentin matrix protein 2), is not phosphorylated by the bacteria and thus provided a means to study the function of the phosphate groups, the major post-translational modification of native PP. The recombinant DMP2 (rDMP2) possessed much lower calcium binding capacity than native PP. Small angle x-ray scattering experiments demonstrated that PP folds to a compact globular structure upon calcium binding, whereas rDMP2 maintained an unfolded structure. In vitro nucleation experiments showed that PP could nucleate plate-like apatite crystals in pseudophysiological buffer, whereas rDMP2 failed to mediate the transformation of amorphous calcium phosphate to apatite crystals under the same experimental conditions. Collagen binding experiments demonstrated that PP favors the formation of collagen aggregates, whereas in the presence of rDMP2 thin fibrils are formed. Overall these results suggested that the phosphate moieties in phosphophoryn are important for its function as a mediator of dentin biomineralization.Mineralization is an essential requirement for the development of the mechanical properties of hard tissues such as bones and teeth. However, on a volume basis, the mineral constitutes only about 50% of a bone; the remaining extracellular organic matrix (ECM) 2 is a hydrated mixture of collagen and noncollagenous matrix proteins (NCPs). The NCPs constitute 5-10% of the total ECM and are associated with the mineral phase so strongly that the tissues need to be demineralized before those proteins can be extracted. The NCPs are mostly acidic proteins, rich in glutamic acid, aspartic acid, and phosphorylated serine/threonine residues, with a high capacity for binding calcium ions and hydroxyapatite crystal surfaces. Therefore, they have been implicated in the regulation of mineral deposition during osteogenesis and dentinogenesis (1). Phosphorylation of threonine and serine residues takes place as a post-translational modification of the core protein via the action of casein kinases (2). found that dentin mineralization was impaired in the presence of casein kinase inhibitors. Thus post-translational phosphorylation of NCPs is crucial for biomineralization.The major phosphoprotein of dentin is the Asp-and Ser-rich protein called phosphophoryn. The name phosphophoryn (PP) was coined to describe its exceedingly high content of phosphate groups. PP, as isolated from dentin, has a unique composition with aspartyl and seryl ...

Bone and dentin biomineralization are well regulated processes mediated by extracellular matrix proteins. It is widely believed that specific matrix proteins in these tissues modulate nucleation of apatite nanoparticles and their growth into micrometer sized crystals via molecular recognition at the protein-mineral interface. However, this assumption has been supported only circumstantially and the exact mechanism remains unknown. Dentin matrix protein 1 (DMP1) is an acidic matrix protein, present in the mineralized matrix of bone and dentin. In the present study we have demonstrated using synchrotron small-angle X-ray scattering that DMP1 in solution can undergo oligomerization and temporarily stabilize the newly formed calcium phosphate nanoparticle precursors by sequestering them and preventing their further aggregation and precipitation. The solution structure represents the first low resolution structural information for DMP1. Atomic force microscopy and transmission electron microscopy studies further confirmed that the nascent calcium phosphate nuclei formed in solution were assembled into ordered protein-mineral complexes with the aid of oligomerized DMP1, recombinant and native. This study reveals a novel mechanism by which DMP1 might facilitate initiation of mineral nucleation at specific sites during bone and dentin mineralization and prevent spontaneous calcium phosphate precipitation in areas in which mineralization is not desirable. KeywordsDentin Matrix Protein 1; Biomineralization; SAXS Mineralized tissue such as bone and dentin are unique biocomposites of a structured organic matrix impregnated with matrix-oriented carbonated apatite crystals (1). The rigidity and compressive strength of bone and dentin are directly dependent upon temporally and spatially controlled mineral nucleation and hierarchically assembled matrix (2,3). It is well known that biological fluids are metastable or supersaturated with respect to calcium salts i.e., they are below the saturation needed for spontaneous precipitation but are well above the saturation to support crystal growth after the initial nucleus has formed (4,5). Therefore, a driving force is required to lower the activation energy of nucleation and formation of thermodynamically To whom correspondence should be addressed. (A.G) Compelling in-vitro and in-vivo data provide evidence that bone and dentin specific noncollagenous proteins play a critical role in the initiation and growth of the calcium phosphate mineral phase (6-8). Although the exact mechanism remains unknown, it is postulated that kinetic control of biomineral crystallization is achieved by interactions between mineral nuclei and soluble or immobilized acidic proteins. Atomic force microscopy indicates that proteins extracted from calcite or aragonite-containing layers of the abalone shell bind to growth sides on well-defined calcium carbonate crystal surfaces and influence the kinetics of crystal growth from solution (9). This protein-mineral interaction might be an essential strate...

Alzheimer's disease (AD) is associated with accumulation of the neurotoxic peptide amyloid-␤ (A␤), which is produced by sequential cleavage of amyloid precursor protein (APP) by the aspartyl protease ␤-secretase and the presenilin-dependent protease ␥-secretase. An increase of casein kinase 1 (CK1) expression has been described in the human AD brain. We show, by using in silico analysis, that APP, ␤-secretase, and ␥-secretase subunits contain, in their intracellular regions, multiple CK1 consensus phosphorylation sites, many of which are conserved among human, rat, and mouse species. Overexpression of constitutively active CK1, one of the CK1 isoforms expressed in brain, leads to an increase in A␤ peptide production. Conversely, three structurally dissimilar CK1-specific inhibitors significantly reduced endogenous A␤ peptide production. By using mammalian cells expressing the ␤ C-terminal fragment of APP, it was possible to demonstrate that CK1 inhibitors act at the level of ␥-secretase cleavage. Importantly, Notch cleavage was not affected. Our results indicate that CK1 represents a therapeutic target for prevention of A␤ formation in AD.␥-cleavage ͉ neurodegenerative ͉ amyloid precursor protein

Dentin matrix protein 1 (DMP1) is a bone-and teethspecific protein initially identified from mineralized dentin. Here we report that DMP1 is primarily localized in the nuclear compartment of undifferentiated osteoblasts. In the nucleus, DMP1 acts as a transcriptional component for activation of osteoblast-specific genes like osteocalcin. During the early phase of osteoblast maturation, Ca 2؉ surges into the nucleus from the cytoplasm, triggering the phosphorylation of DMP1 by a nuclear isoform of casein kinase II. This phosphorylated DMP1 is then exported out into the extracellular matrix, where it regulates nucleation of hydroxyapatite. Thus, DMP1 is a unique molecule that initiates osteoblast differentiation by transcription in the nucleus and orchestrates mineralized matrix formation extracellularly, at later stages of osteoblast maturation. The data presented here represent a paradigm shift in the understanding of DMP1 function. This information is crucial in understanding normal bone formation, remodeling, fracture healing, and skeletal tissue repair.Mesenchymal stem cells have the potential to differentiate into several cell types that give rise to bone, cartilage, fat, and muscles. Proliferation and differentiation of mesenchymal cells to osteoblastic lineage is regulated by an intrinsic genetically defined program, which is well-controlled by various transcription factors, cytokines, morphogens, and secreted growth factors. There are two known transcription factors, namely Cbfa1 and osterix, that regulate osteoblast differentiation and skeletal formation during embryonic development (1). Cbfa1-deficient mice have an osteopenic skeleton (2) and are known to regulate the expression of bone sialoprotein, osteopontin, dentin matrix protein 1, osteocalcin, and collagen type I (3). Recently osterix has been shown to act downstream of Cbfa1 and functions to regulate the differentiation of preosteoblasts into mature osteoblasts (4). Differentiated osteoblasts synthesize a number of calcium-binding proteins like bone sialoprotein, osteopontin, and osteocalcin and secrete a complex extracellular matrix that has the capacity to nucleate hydroxyapatite crystal formation when adequate amounts of calcium and phosphate are supplied (reviewed in Ref. 5). Understanding the regulatory mechanisms that control differentiation of osteoblast phenotype during proliferation, maturation, and mineralization is necessary for understanding various skeletal disorders. MC3T3-E1 cells are a well-established preosteoblast cell line derived from mouse calvaria and maintain much of the tightly linked controls between proliferation and differentiation. These cells, when treated with ␤-glycerophosphate and ascorbic acid, differentiate into mature osteoblast phenotype and produce a calcifiable matrix that recapitulates in vivo conditions. Mineralized nodule formation takes place at least 18 -21 days after induction of mineralization. During the early stage (3-5 days) of induction the preosteoblastic cells undergo proliferation, and at later...