Cephalopod-Mimetic Tunable Photonic Coatings Assembled from Quasi-Monodispersed Reflectin Protein Nanoparticles.

The remarkable dynamic camouflage ability of cephalopods arises from precisely orchestrated structural changes within their chromatophores and iridophores photonic cells. This mesmerizing color display remains unmatched in synthetic coatings and is regulated by swelling/deswelling of reflectin protein nanoparticles, which alters platelet dimensions in iridophores to control photonic patterns according to Bragg's law. Toward mimicking the photonic response of squid's skin, reflectin proteins from Sepioteuthis lessioniana were sequenced, recombinantly expressed, and self-assembled into spherical nanoparticles by conjugating reflectin B1 with a click chemistry ligand. These quasi-monodisperse nanoparticles can be tuned to any desired size in the 170-1000 nm range. Using Langmuir-Schaefer and drop-cast deposition methods, ligand-conjugated reflectin B1 nanoparticles were immobilized onto azide-functionalized substrates via click chemistry to produce monolayer amorphous photonic structures with tunable structural colors based on average particle size, paving the way for the fabrication of eco-friendly, bioinspired color-changing coatings that mimic cephalopods' dynamic camouflage.

A diecast mineralization process forms the tough mantis shrimp dactyl club.

Biomineralization, the process by which mineralized tissues grow and harden via biogenic mineral deposition, is a relatively lengthy process in many mineral-producing organisms, resulting in challenges to study the growth and biomineralization of complex hard mineralized tissues. Arthropods are ideal model organisms to study biomineralization because they regularly molt their exoskeletons and grow new ones in a relatively fast timescale, providing opportunities to track mineralization of entire tissues. Here, we monitored the biomineralization of the mantis shrimp dactyl club-a model bioapatite-based mineralized structure with exceptional mechanical properties-immediately after ecdysis until the formation of the fully functional club and unveil an unusual development mechanism. A flexible membrane initially folded within the club cavity expands to form the new club's envelope. Mineralization proceeds inwards by mineral deposition from this membrane, which contains proteins regulating mineralization. Building a transcriptome of the club tissue and probing it with proteomic data, we identified and sequenced Club Mineralization Protein 1 (CMP-1), an abundant mildly phosphorylated protein from the flexible membrane suggested to be involved in calcium phosphate mineralization of the club, as indicated by in vitro studies using recombinant CMP-1. This work provides a comprehensive picture of the development of a complex hard tissue, from the secretion of its organic macromolecular template to the formation of the fully functional club.

Hierarchical Assembly of Tough Bioelastomeric Egg Capsules is Mediated by a Bundling Protein.

Marine snail egg capsules are shock-absorbing bioelastomers made from precursor "egg case proteins" (ECPs) that initially lack long-range order. During capsule formation, these proteins self-assemble into coiled-coil filaments that subsequently align into microscopic layers, a multiscale process which is crucial to the capsules' shock-absorbing properties. In this study, we show that the self-assembly of ECPs into their functional capsule material is mediated by a bundling protein that facilitates the aggregation of coiled-coil building blocks and their gelation into a prefinal capsule prior to final stabilization. This low molecular weight bundling protein, termed Pugilina cochlidium Bundling Protein (PcBP), led to gelation of native extracts from gravid snails, whereas crude extracts lacking PcBP did not gelate and remained as a protein solution. Refolding and reconcentration of recombinant PcBP induced bundling and aggregation of ECPs, as evidenced by ECPs oligomerization. We propose that the secretion of PcBP in vivo is a time-specific event during the embryo encapsulation process prior to cross-linking in the ventral pedal gland (VPG). Using molecular dynamics (MD) simulations, we further propose plausible disulfide binding sites stabilizing two PcBP monomers, as well as a polarized surface charge distribution, which we suggest plays an important role in the bundling mechanism. Overall, this study shows that controlled bundling is a key step during the extra-cellular self-assembly of egg capsules, which has previously been overlooked.

Integrative and comparative analysis of coiled-coil based marine snail egg cases - a model for biomimetic elastomers.

Integrative and comparative analyses of biomaterials systems offer the potential to reveal conserved elements that are essential for mechanical function. The approach also affords the opportunity to identify variation in designs at multiple length scales, enabling the delineation of a range of parameters for creating precisely tuned biomimetic materials. We investigated the molecular design and structural hierarchy of elastomeric egg capsules from the marine snail Pugilina cochlidium (family Melongenidae) and compared these data with all available published studies in order to infer the structure-property relationships of the egg case from the molecular to the macroscopic scale. While mechanical similarities had previously been observed for two other marine melongenid snails, Busycotypus canaliculatus and Busycon carica, B. canaliculatus was the only species for which detailed molecular and nanostructural data were available. Egg capsules from P. cochlidium were found to exhibit mechanical properties and shock absorbing potential that was similar to B. canaliculatus. The two species also displayed similarity in hierarchical fibril bundling and a sub-micron staggering of 100-105 nm within filaments, as shown by atomic force microscopy and small angle X-ray diffraction. In situ Raman micro spectroscopy indicated that P. cochlidium egg cases undergo a stress-induced coiled-coil to extended ß-strand structural transformation that is very similar to that of B. canaliculatus. These observations supported the view that these structural and hierarchical elements are essential for egg case function. Comparative analysis of the primary amino acid sequences and structural predictions for all known egg case proteins suggested that while the proteins all contain sequences prone to adopt α-helical structures, the predicted location of coiled-coil domains and stutter perturbations varied within and between species. Despite these differences, mixtures of denatured native egg case proteins readily re-folded in citrate-phosphate assembly buffer into α-helix rich, coiled-coil based oligomers, as determined by attenuated total reflection Fourier transform infrared spectroscopy, circular dichroism and MALDI-TOF. It is concluded that both conserved and divergent designs in marine snail egg cases offer inspiration for the engineering of biomimetic elastomeric materials with a unique capability for mechanical energy absorption.