Effect of Gel Exposition on Calcium and Carbonate Ions Determines the Stm-l Effect on the Crystal Morphology of Calcium Carbonate.

Biomineralization of fish otoliths is regulated by macromolecules, such as proteins, whose presence is crucial for the functionality and properties of these mineralized structures. Special regulatory effects are exerted by intrinsically disordered proteins, such as the polyanionic Starmaker-like protein from medaka, a homolog of zebrafish Starmaker. In this study, we employed a set of bioinspired mineralization experiments with a single diffusion system to investigate the effect of the Starmaker-like protein on calcium carbonate biominerals with regards to the prior exposition of the protein to calcium or carbonate ions. Interestingly, the bioinspired minerals grown in the presence of the Starmaker-like protein in calcium- or carbonate-type experiments differ significantly in terms of morphology and protein distribution within the crystals. Our deeper analysis shows that the Starmaker-like protein action is a result of the environmental conditions to which it is exposed. These findings may be of special interest in the areas of biomineralization process pathways and biomaterial sciences.

Functional derivatives of human dentin matrix protein 1 modulate morphology of calcium carbonate crystals.

Dentin matrix protein 1 (DMP1) is an acidic, extracellular matrix protein essential for biomineralization of calcium phosphate, in bone and dentin. It is proteolytically processed into two fragments, 44K and 56K. Recently, the presence of DMP1 was noticed in inner ear, specifically in otoconia, which are calcium carbonate biominerals involved in sensing of balance. In this study, the solution structure and biomineralization activity of otoconial 44K and 56K fragments toward calcium carbonate were investigated. The results of analytical ultracentrifugation, circular dichroism, and gel filtration indicated that DMP1 fragments are disordered in solution. Notably, 56K formed oligomers in the presence of calcium ions. It was also observed that both fragments influenced the crystal growth by in vitro biomineralization assay and scanning electron microscopy. In addition, they sequester the calcium ions during the calcite formation. Calcium carbonate crystals precipitated in vitro changed their size and shape in the presence of DMP1 fragments. Oligomerization propensity of 56K may significantly enhance this function. Our study indicates that intrinsically disordered DMP1 has a previously unknown regulatory function for biomineralization of otoconia.

Lattice Shrinkage by Incorporation of Recombinant Starmaker-Like Protein within Bioinspired Calcium Carbonate Crystals.

The biological mediation of mineral formation (biomineralization) is realized through diverse organic macromolecules that guide this process in a spatial and temporal manner. Although the role of these molecules in biomineralization is being gradually revealed, the molecular basis of their regulatory function is still poorly understood. In this study, the incorporation and distribution of the model intrinsically disordered starmaker-like (Stm-l) protein, which is active in fish otoliths biomineralization, within calcium carbonate crystals, is revealed. Stm-l promotes crystal nucleation and anisotropic tailoring of crystal morphology. Intracrystalline incorporation of Stm-l protein unexpectedly results in shrinkage (and not expansion, as commonly described in biomineral and bioinspired crystals) of the crystal lattice volume, which is described herein, for the first time, for bioinspired mineralization. A ring pattern was observed in crystals grown for 48 h; this was composed of a protein-enriched region flanked by protein-depleted regions. It can be explained as a result of the Ostwald-like ripening process and intrinsic properties of Stm-l, and bears some analogy to the daily growth layers of the otolith.

[Biomineralization--precision of shape, structure and properties controlled by proteins]. / Biomineralizacja--kontrolowana przez bialka precyzja ksztaltu, struktury i wlasciwosci.

ABSTRACT Biomineralization is the process of the formation of crystal structures that is under biological control. Living organisms produce structures such as bone, teeth, otoliths, otoconia or shells. Although the chemical composition of these tissues is similar to corresponding inorganic minerals, their structure and mechanical properties differ significantly. This may be because of how they are adapted for the functions they perform. The precise control of the formation of biominerals starting with the early nucleation stage influences how the final tissues are formed. The key factors which determine the size, shape, internal structure and properties of biominerals are proteins which control the nucleation and growth of the crystals. Biomineralization is a multi-step process involving protein-protein interactions, as well as interactions between proteins and inorganic fraction. Due to their specific properties, intrinsically disordered proteins (IDPs) perform a particularly important role in the control of the biomineralization process. This article contains an overview of biominerals that are naturally occurring and describes the structures and mineralization mechanisms of the most important of them. The main part of this work was dedicated to the role of proteins which control crystal growth.

One- and Two-Photon Excited Autofluorescence of Lysozyme Amyloids.

Autofluorescence properties of amyloid fibrils are of much interest but, to date, the attention has been given mostly to one-photon excited fluorescence (1PEF), while the two-photon excited fluorescence (2PEF) properties of amyloids are much less explored. We investigate 1PEF and 2PEF of hen egg-white lysozyme (HEWL) in the form of monomers and fibrils. HEWL monomers feature some autofluorescence, which is enhanced in the case of fibrils. Moreover, by varying NaCl content, we introduce changes to fibrils morphology and show how the increase of the salt concentration is linked with an increase of 1PEF and 2PEF intensities. Interestingly, we observe 2PEF emission red-shifted in comparison to 1PEF. We confirm the presence of different relaxation pathways upon one- or two-photon excitation by different lifetimes of the fluorescence decays. Finally, we correlate the changes in optical properties of HEWL fibrils and monomers with salt-mediated changes in their morphology and the secondary structure.

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.

Non-toxic Polymeric Dots with the Strong Protein-Driven Enhancement of One- and Two-Photon Excited Emission for Sensitive and Non-destructive Albumin Sensing.

The need for efficient probing, sensing, and control of the bioactivity of biomolecules (e.g., albumins) has led to the engineering of new fluorescent albumins' markers fulfilling very specific chemical, physical, and biological requirements. Here, we explore acetone-derived polymer dots (PDs) as promising candidates for albumin probes, with special attention paid to their cytocompatibility, two-photon absorption properties, and strong ability to non-destructively interact with serum albumins. The PDs show no cytotoxicity and exhibit high photostability. Their pronounced green fluorescence is observed upon both one-photon excitation (OPE) and two-photon excitation (TPE). Our studies show that both OPE and TPE emission responses of PDs are proteinaceous environment-sensitive. The proteins appear to constitute a matrix for the dispersion of fluorescent PDs, limiting both their aggregation and interactions with the aqueous environment. It results in a large enhancement of PD fluorescence. Meanwhile, the PDs do not interfere with the secondary protein structures of albumins, nor do they induce their aggregation, enabling the PD candidates to be good nanomarkers for non-destructive probing and sensing of albumins.

pH-Induced transformation of ligated Au25 to brighter Au23 nanoclusters.

Thiolate-protected gold nanoclusters have recently attracted considerable attention due to their size-dependent luminescence characterized by a long lifetime and large Stokes shift. However, the optimization of nanocluster properties such as the luminescence quantum yield is still a challenge. We report here the transformation of Au25Capt18 (Capt labels captopril) nanoclusters occurring at low pH and yielding a product with a much increased luminescence quantum yield which we have identified as Au23Capt17. We applied a simple method of treatment with HCl to accomplish this transformation and we characterized the absorption and emission of the newly created ligated nanoclusters as well as their morphology. Based on DFT calculations we show which Au nanocluster size transformations can lead to highly luminescent species such as Au23Capt17.

Single-molecule electrometry.

Mass and electrical charge are fundamental properties of biological macromolecules. Although molecular mass has long been determined with atomic precision, a direct and precise determination of molecular charge remains an outstanding challenge. Here we report high-precision (<1e) measurements of the electrical charge of molecules such as nucleic acids, and globular and disordered proteins in solution. The measurement is based on parallel external field-free trapping of single macromolecules, permits the estimation of a dielectric coefficient of the molecular interior and can be performed in real time. Further, we demonstrate the direct detection of single amino acid substitution and chemical modifications in proteins. As the electrical charge of a macromolecule strongly depends on its three-dimensional conformation, this kind of high-precision electrometry offers an approach to probe the structure, fluctuations and interactions of a single molecule in solution.

Intrinsically disordered and pliable Starmaker-like protein from medaka (Oryzias latipes) controls the formation of calcium carbonate crystals.

Fish otoliths, biominerals composed of calcium carbonate with a small amount of organic matrix, are involved in the functioning of the inner ear. Starmaker (Stm) from zebrafish (Danio rerio) was the first protein found to be capable of controlling the formation of otoliths. Recently, a gene was identified encoding the Starmaker-like (Stm-l) protein from medaka (Oryzias latipes), a putative homologue of Stm and human dentine sialophosphoprotein. Although there is no sequence similarity between Stm-l and Stm, Stm-l was suggested to be involved in the biomineralization of otoliths, as had been observed for Stm even before. The molecular properties and functioning of Stm-l as a putative regulatory protein in otolith formation have not been characterized yet. A comprehensive biochemical and biophysical analysis of recombinant Stm-l, along with in silico examinations, indicated that Stm-l exhibits properties of a coil-like intrinsically disordered protein. Stm-l possesses an elongated and pliable structure that is able to adopt a more ordered and rigid conformation under the influence of different factors. An in vitro assay of the biomineralization activity of Stm-l indicated that Stm-l affected the size, shape and number of calcium carbonate crystals. The functional significance of intrinsically disordered properties of Stm-l and the possible role of this protein in controlling the formation of calcium carbonate crystals is discussed.