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A number of marine organisms use muscle-controlled surface structures to achieve rapid changes in colour and transparency with outstanding reversibility. Inspired by these display tactics, we develop analogous deformation-controlled surface-engineering approaches via strain-dependent cracks and folds to realize the following four mechanochromic devices: (1) transparency change mechanochromism (TCM), (2) luminescent mechanochromism (LM), (3) colour alteration mechanochromism (CAM) and (4) encryption mechanochromism (EM). These devices are based on a simple bilayer system that exhibits a broad range of mechanochromic behaviours with high sensitivity and reversibility. The TCM device can reversibly switch between transparent and opaque states. The LM can emit intensive fluorescence as stretched with very high strain sensitivity. The CAM can turn fluorescence from green to yellow to orange as stretched within 20% strain. The EM device can reversibly reveal and conceal any desirable patterns. Muscle-controlled changes in surface structures are employed in nature to achieve rapid, reversible changes in colour and transparency. Here the authors develop a simple, bilayer platform capable of several distinct analogous mechanochromic behaviours.

The squid beak displays a 200-fold stiffness gradient across its length. A battery of experiments, including ‘omics analysis and rheological measurements, now identifies two protein families that infiltrate and cross-link a porous chitin network to generate variable stiffness. The beak of the jumbo squid Dosidicus gigas is a fascinating example of how seamlessly nature builds with mechanically mismatched materials. A 200-fold stiffness gradient begins in the hydrated chitin of the soft beak base and gradually increases to maximum stiffness in the dehydrated distal rostrum. Here, we combined RNA-Seq and proteomics to show that the beak contains two protein families. One family consists of chitin-binding proteins (DgCBPs) that physically join chitin chains, whereas the other family comprises highly modular histidine-rich proteins (DgHBPs). We propose that DgHBPs play multiple key roles during beak bioprocessing, first by forming concentrated coacervate solutions that diffuse into the DgCBP-chitin scaffold, and second by inducing crosslinking via an abundant GHG sequence motif. These processes generate spatially controlled desolvation, resulting in the impressive biomechanical gradient. Our findings provide novel molecular-scale strategies for designing functional gradient materials.

The evolution of new traits enables expansion into new ecological and behavioural niches. Nonetheless, demonstrated connections between divergence in protein structure, function and lineage-specific behaviours remain rare. Here we show that both octopus and squid use cephalopod-specific chemotactile receptors (CRs) to sense their respective marine environments, but structural adaptations in these receptors support the sensation of specific molecules suited to distinct physiological roles. We find that squid express ancient CRs that more closely resemble related nicotinic acetylcholine receptors, whereas octopuses exhibit a more recent expansion in CRs consistent with their elaborated ‘taste by touch’ sensory system. Using a combination of genetic profiling, physiology and behavioural analyses, we identify the founding member of squid CRs that detects soluble bitter molecules that are relevant in ambush predation. We present the cryo-electron microscopy structure of a squid CR and compare this with octopus CRs 1 and nicotinic receptors 2 . These analyses demonstrate an evolutionary transition from an ancestral aromatic ‘cage’ that coordinates soluble neurotransmitters or tastants to a more recent octopus CR hydrophobic binding pocket that traps insoluble molecules to mediate contact-dependent chemosensation. Thus, our study provides a foundation for understanding how adaptation of protein structure drives the diversification of organismal traits and behaviour. Octopus and squid use cephalopod-specific chemotactile receptors to sense their respective marine environments, but structural adaptations in these receptors support the sensation of specific molecules suited to distinct physiological roles.

Ubiquitous use of electronic devices has led to an unprecedented increase in related waste as well as the worldwide depletion of reserves of key chemical elements required in their manufacturing. The use of biodegradable and abundant organic (carbon-based) electronic materials can contribute to alleviate the environmental impact of the electronic industry. The pigment eumelanin is a bio-sourced candidate for environmentally benign (green) organic electronics. The biodegradation of eumelanin extracted from cuttlefish ink is studied both at 25 °C (mesophilic conditions) and 58 °C (thermophilic conditions) following ASTM D5338 and comparatively evaluated with the biodegradation of two synthetic organic electronic materials, namely copper (II) phthalocyanine (Cu–Pc) and polyphenylene sulfide (PPS). Eumelanin biodegradation reaches 4.1% (25 °C) in 97 days and 37% (58 °C) in 98 days, and residual material is found to be without phytotoxic effects. The two synthetic materials, Cu–Pc and PPS, do not biodegrade; Cu–Pc brings about the inhibition of microbial respiration in the compost. PPS appears to be potentially phytotoxic. Finally, some considerations regarding the biodegradation test as well as the disambiguation of “biodegradability” and “bioresorbability” are highlighted.

The beak of the Humboldt squid Dosidicus gigas represents one of the hardest and stiffest wholly organic materials known. As it is deeply embedded within the soft buccal envelope, the manner in which impact forces are transmitted between beak and envelope is a matter of considerable scientific interest. Here, we show that the hydrated beak exhibits a large stiffness gradient, spanning two orders of magnitude from the tip to the base. This gradient is correlated with a chemical gradient involving mixtures of chitin, water, and His-rich proteins that contain 3,4-dihydroxyphenyl-L-alanine (dopa) and undergo extensive stabilization by histidyl-dopa cross-link formation. These findings may serve as a foundation for identifying design principles for attaching mechanically mismatched materials in engineering and biological applications.

In recent years, arginine-rich basic proteins have garnered significant attention due to their essential roles in various biological processes. However, the potential of marine-derived proteins in this domain remains largely unexplored. This study presents, for the first time, the isolation and purification of a 14.3 kDa protamine (SOP) from the mature spermatogonial tissues of Symplectoteuthis oualaniensis. Additionally, we obtained an 18.5 kDa PEGylated derivative, SOP-PEG. The physicochemical properties of both SOP and SOP-PEG were comprehensively characterized using SEM, FTIR, CD, and TGA. PEGylation markedly altered the surface morphology, secondary structure, and thermal stability of SOP. In vitro studies demonstrated that PEGylation significantly enhanced the biocompatibility of SOP, leading to improved proliferation of L-929 fibroblasts. Furthermore, both SOP and its PEGylated derivative (SOP-PEG) regulated the cell cycle, activated the PI3K-Akt signaling pathway, and modulated anti-apoptotic mechanisms, suggesting their potential to support cell survival and facilitate tissue regeneration. Notably, SOP-PEG exhibited superior bioactivity, likely attributable to its enhanced delivery efficiency conferred by PEGylation. Collectively, these findings underscore the promising applications of SOP and SOP-PEG in regenerative medicine and highlight the pivotal role of PEGylation in augmenting the bioactivity of SOP.

Invertebrate phototransduction uses an inositol-1,4,5-trisphosphate signalling cascade in which photoactivated rhodopsin stimulates a G q -type G protein, that is, a class of G protein that stimulates membrane-bound phospholipase Cβ. The same cascade is used by many G-protein-coupled receptors, indicating that invertebrate rhodopsin is a prototypical member. Here we report the crystal structure of squid ( Todarodes pacificus ) rhodopsin at 2.5 Å resolution. Among seven transmembrane α-helices, helices V and VI extend into the cytoplasmic medium and, together with two cytoplasmic helices, they form a rigid protrusion from the membrane surface. This peculiar structure, which is not seen in bovine rhodopsin, seems to be crucial for the recognition of G q -type G proteins. The retinal Schiff base forms a hydrogen bond to Asn 87 or Tyr 111; it is far from the putative counterion Glu 180. In the crystal, a tight association is formed between the amino-terminal polypeptides of neighbouring monomers; this intermembrane dimerization may be responsible for the organization of hexagonally packed microvillar membranes in the photoreceptor rhabdom. Squid rhodopsin: A structure for signal transduction The rhodopsins found in the invertebrate eye are light-activated G-protein-coupled receptors, whose activity is coupled to G q -type G-proteins. Midori Murakami and Tsutomu Kouyama now report the crystal structure of squid rhodopsin, at 2.5 Å, in which a putative G-protein-binding site is resolved. The newly obtained structure could help explain one of the novel properties of the invertebrate eye, the ability to detect the direction of the polarization plane of visible light. Invertebrate rhodopsins are light-activated G-protein-coupled receptors, whose activity is coupled to Gq-type G-proteins. This paper reports the crystal structure of squid rhodopsin, at 2.5 Å, in which a putative G-protein-binding site is resolved.

Background: Hypertension has been identified as a significant risk factor for cardiovascular disease. Given the prevalence of the adverse effects of angiotensin-converting enzyme-inhibitory (ACEI) drugs, natural and effective alternatives to these medications need to be identified. Methods: An investigative study was conducted to assess the ACEI capacity and structural characteristics of enzymatic hydrolysates with varying molecular weights derived from squid skin. The amino acid sequences of the enzymatic digests were analyzed via Nano LC-MS/MS and screened for peptides with ACEI activity using an in silico analysis. Furthermore, molecular docking was employed to investigate the interaction between potential ACEI peptides and ACE. Results: TPSH-V (MW < 1 kDa) exhibited the highest rate of ACEI, a property attributable to its substantial hydrophobic amino acid content. Additionally, TPSH-V exhibited high temperature and pH stability, indicative of regular ordering in its secondary structure. The binding modes of four potential novel ACEI peptides to ACE were predicted via molecular docking with the sequences of FHGLPAK, IIAPPERKY, RGLPAYE, and VPSDVEF, all of which can bind to the ACE active site via hydrogen bonding, with FHGLPAK, RGLPAYE, and VPSDVEF being able to coordinate with Zn2+. Conclusions: Squid skin constitutes a viable resource for the production of ACEI peptides.

Squid pen (SP) was found to contain 64.41% protein and 26.03% chitin. The amino acid composition revealed that Met was the most abundant amino acid in SP, with a concentration of 13.67 g/100 g. To enhance the stability and bioavailability of SP hydrolysates, microcapsules were developed using ultrasonic emulsification techniques with SP trypsin hydrolysates (SPTH) and SP β-chitosan (SPC). The optimal preparation conditions involved using a 2% concentration of SPC, a 4 mg/mL concentration of SPTH, a core-to-wall ratio (v/v) of 1:3 for SPTH/SPC, and subjecting them to ultrasonic treatment for 20 min. These microcapsules had a loading capacity of 58.95% for SPTH under these conditions. The successful encapsulation of SPTH in the SPC complex to form SPC-SPTH microcapsules was confirmed by FTIR, XRD, DSC, and SEM, exhibiting good thermal stability, small particle size, and high encapsulation efficiency. In vitro digestion studies demonstrated a release of 15.61% in simulated gastric fluid and 69.32% in intestinal fluid, achieving targeted release in the intestines. The digested products exhibited superior antioxidant activity compared to free SPTH digests, suggesting that microencapsulation effectively preserves SPTH bioactivity. This study enhances the bioavailability of SPTH and offers a promising delivery system for natural compounds with low bioavailability and stability.

The squid, Sepioteuthis lessoniana , is a remarkable fishery product which is exported by many nations for use in industrial production or human consumption. This study focused on the synthesis of silver nanoparticles (AgNPs) from squid ink (SI) and its wide range of applications. The formation of the nanoparticles was confirmed through UV–Visible spectroscopy, FTIR, XRD, SEM with EDX, DLS, and zeta potential analysis. The results showed a strong absorbance peak at 407 nm, the presence of various functional groups, a nanocrystalline structure with a crystalline size of 17.56 nm, spherical-shaped particles with an average size of 76 nm, and the presence of the highest % mass of Ag and uniformly dispersed particles, respectively. The bioactivity of the synthesized squid ink silver nanoparticles was analyzed through antibacterial, antioxidant, anticancer, and toxicity studies. The dye degradation assay was also analyzed as a means of wastewater treatment for different industrial dyes. The antibacterial activity showed the highest zone of inhibition of 24 mm at a concentration of 100 μg/ml against Escherichia coli , followed by other tested strains. The nitric oxide radical scavenging assay showed the highest antioxidant activity (92%) at a concentration of 100 μg/ml. The cytotoxic ability of SI-AgNPs against the MDA-MB-231 breast cancer cell line revealed an IC 50 value of 4.52 μg/ml. The toxicity study revealed a dose and time-dependent activity with the LC 50 value of 5.090 and 3.303 mg/ml for 24 and 48 h, respectively. The successful degradation of dyes by SI-AgNPs is attributed to the cooperative action of the electron relay system with Ag as a catalyst and SI as a catalytic support. These findings indicate that SI-AgNPs are a novel potential product that should be further studied to improve its pharmacological, biomedical, and environmental applications.