Control of nacre biomineralization by Pif80 in pearl oyster

Molluscan nacre is a fascinating biomineral consisting of a highly organized calcium carbonate composite that provides unique fracture toughness and an iridescent color. Organisms elaborately control biomineralization using organic macromolecules. We propose the involvement of the matrix protein Pif80 from the pearl oyster Pinctada fucata in the development of the inorganic phase during nacre biomineralization, based on experiments using the recombinant form of Pif80. Through interactions with calcium ions, Pif80 participates in the formation of polymer-induced liquid precursor-like amorphous calcium carbonate granules and stabilizes these granules by forming calcium ion-induced coacervates. At the calcification site, the disruption of Pif80 coacervates destabilizes the amorphous mineral precursors, resulting in the growth of a crystalline structure. The redissolved Pif80 controls the growth of aragonite on the polysaccharide substrate, which contributes to the formation of polygonal tablet structure of nacre. Our findings provide insight into the use of organic macromolecules by living organisms in biomineralization.117Ysciescopu

A bioinspired dual-crosslinked tough silk protein hydrogel as a protective biocatalytic matrix for carbon sequestration

The development of carbonic anhydrase (CA)-based materials for the environment-friendly sequestration of carbon dioxide (CO2) under mild conditions would be highly valuable for controlling emissions to the environment and for producing value-added chemicals. Here, a highly tough and stable CA-encapsulating silk protein hydrogel was developed as a robust biocatalyst for CO2 sequestration through a bioinspired dual-crosslinking strategy that employed photoinduced dityrosine chemical crosslinking followed by dehydration-mediated physical crosslinking. The target enzyme was efficiently encapsulated in the silk hydrogel with similar to 60% retention of the activity of free CA, and the encapsulated CA exhibited excellent overall multi-use, storage and thermal stabilities. The dual-crosslinked CA-encapsulating silk hydrogel exhibited a significant compressive modulus, which surpassed the moduli of most traditional and double-network hydrogels as well as those of enzyme-encapsulated hydrogels. This hydrogel also showed high resiliency and elasticity and outstanding structural stability. Importantly, the dual-crosslinked CA-encapsulating silk hydrogel facilitated the sequestration of CO2 into calcium carbonate with high CO2 hydration activity. Thus, the unique combination of bioinspired dual-crosslinking with silk fibroin protein and CA enzyme demonstrates the successful application of this protein hydrogel as a promising biocatalyst for CO2 sequestration by showing high activity, strong mechanical properties and outstanding structural stability.116Nsciescopu

CaCO3 thin-film formation mediated by a synthetic protein-lysozyme coacervate

Coacervation is a liquid-liquid phase separation process of macromolecular polyelectrolytes. The formation of simple and complex coacervates of a synthetic acidic protein, GG1234, as a model shell matrix protein, was investigated using turbidity measurements and microscopic morphological observations. Simple coacervation of GG1234 was optimally induced at pH 3.75 and below 50 mM for all of the tested salts, and complex coacervates were prepared at pH 4-9 in sodium acetate solution at various ratios of GG1234 to lysozyme without inducing simple coacervation. The complex coacervates also had the ability to microencapsulate hydrophobic oil droplets in a similar manner to that of other complex coacervation systems. Remarkably, a thin film was formed through in vitro CaCO3 crystallization in the presence of complex coacervates, which was expected to be planar and poorly crystalline CaCO3 guided at the interface of two immiscible liquid phases upon complex coacervation. Collectively, our results indicate that our synthetic acidic matrix protein can be used as the main protein for simple and complex coacervations, and the coacervates of this protein may be involved in thin film formation in CaCO3 crystallization.11Ysciescopu

Role of Pif97 in Nacre Biomineralization: In Vitro Characterization of Recombinant Pif97 as a Framework Protein for the Association of Organic–Inorganic Layers in Nacre

Nacre is the inner layer of the mollusc shell and provides exceptional toughness via its highly organized organic–inorganic composite structure. Pif is an organic matrix protein from the nacreous layer of the pearl oyster Pinctada fucata and exhibits regulatory behavior in nacre formation. Here, we investigated features of Pif97, the N-terminal of Pif, using a recombinant form of Pif97 produced in Escherichia coli. We observed that recombinant Pif97 was able to efficiently form a complex with calcium ions. Additionally, recombinant Pif97 showed both in vitro growth inhibition of thermodynamically stable calcite, stabilization of amorphous calcium carbonate, and exclusive binding affinity to metastable aragonite and chitin. These results imply the participation of Pif97 in the calcification of nacre including the association of the inorganic phase and polysaccharide template. We propose that recombinant Pif97 has inherent characteristics of the native form, which are significant for interrelating with organic matrix and inorganic calcium carbonate during nacre biomineralization