Squid Sucker Ring Teeth Research Articles

Molecular Insights into the Self-Assembly of Block Copolymer Suckerin Polypeptides into Nanoconfined β-Sheets.

Suckerin in squid sucker ring teeth is a block-copolymer peptide comprised of two repeating modules-the alanine and histidine-rich M1 and the glycine-rich M2. Suckerin self-assemblies display excellent thermo-plasticity and pH-responsive properties, along with the high biocompatibility, biodegradability, and sustainability. However, the self-assembly mechanism and the detailed role of each module are still elusive, limiting the capability of applying and manipulating such biomaterials. Here, the self-assembly dynamics of the two modules and two minimalist suckerin-mimetic block-copolymers, M1-M2-M1 and M2-M1-M2, in silico is investigated. The simulation results demonstrate that M2 has a stronger self-association but weaker β-sheet propensities than M1. The high self-assembly propensity of M2 allows the minimalist block-copolymer peptides to coalesce with microphase separation, enabling the formation of nanoconfined β-sheets in the matrix formed by M1-M2 contacts. Since these glycine-rich fragments with scatted hydrophobic and aromatic residues are building blocks of many other block-copolymer peptides, the study suggests that these modules function as the "molecular glue" in addition to the flexible linker or spacer to drive the self-assembly and microphase separation. The uncovered molecular insights may help understand the structure and function of suckerin and also aid in the design of functional block-copolymer peptides for nanotechnology and biomedicine applications.

Marine Structural Protein Stability Induced by Hofmeister Salt Annealing and Enzymatic Cross-Linking.

The Humboldt squid is one of the fiercest marine predators thanks in part to its sucker ring teeth that are biopolymer blends of a protein isoform family called suckerin with compression strength that rivals silkworm silk. Here, we focus on the popular suckerin-12 isoform to understand what makes the secondary structure of this biopolymer different in water and the potential role of diverse physical and chemical cross-linkings. By choosing a salt post-treatment, in accordance with the Hofmeister series, we achieved film stability with salt annealing that is comparable to chemical cross-links. By correlating the film morphology with the protein secondary structure changes, suckerin-12 films were shown to contract upon treatment with kosmotropic salts and exhibited increased stability in water. These changes are related to the rearrangement of suckerin-12 secondary structure from random coils and helices to β-sheets. Overall, understanding secondary structure changes caused by aqueous and ionic environments can be instructive for the tuning of the suckerin film sclerotization, its conversion to a tough biological material, and to ultimately produce the natural squid sucker ring teeth.

A Short Peptide Hydrogel with High Stiffness Induced by 310-Helices to β-Sheet Transition in Water.

Biological gels generally require polymeric chains that produce long‐lived physical entanglements. Low molecular weight colloids offer an alternative to macromolecular gels, but often require ad‐hoc synthetic procedures. Here, a short biomimetic peptide composed of eight amino acid residues derived from squid sucker ring teeth proteins is demonstrated to form hydrogel in water without any cross‐linking agent or chemical modification and exhibits a stiffness on par with the stiffest peptide hydrogels. Combining solution and solid‐state NMR, circular dichroism, infrared spectroscopy, and X‐ray scattering, the peptide is shown to form a supramolecular, semiflexible gel assembled from unusual right‐handed 310‐helices stabilized in solution by π–π stacking. During gelation, the 310‐helices undergo conformational transition into antiparallel β‐sheets with formation of new interpeptide hydrophobic interactions, and molecular dynamic simulations corroborate stabilization by cross β‐sheet oligomerization. The current study broadens the range of secondary structures available to create supramolecular hydrogels, and introduces 310‐helices as transient building blocks for gelation via a 310‐to‐β‐sheet conformational transition.

Anion-Mediated Effects on the Size and Mechanical Properties of Enzymatically Crosslinked Suckerin Hydrogels.

The suckerin family of proteins, identified from the squid sucker ring teeth assembly, offers unique mechanical properties and potential advantages over other natural biomaterials. In this study, a small suckerin isoform, suckerin-12, is used to create enzymatically crosslinked, macro-scale hydrogels. Upon exposure to specific salt conditions, suckerin-12 hydrogels contracted into a condensed state where mechanical properties are found to be modulated by the salt anion present. The rate of contraction is found to correlate well with the kosmotropic arm of the Hofmeister anion series. However, the observed changes in hydrogel mechanical properties are better explained by the ability of the salt to neutralize charges in suckerin-12 by deprotonization or charge screening. Thus, by altering the anions in the condensing salt solution, it is possible to tune the mechanical properties of suckerin-12 hydrogels. The potential for suckerins to add new properties to materials based on naturally-derived proteins is highlighted.

Controlling Supramolecular Chiral Nanostructures by Self-Assembly of a Biomimetic β-Sheet-Rich Amyloidogenic Peptide.

Squid sucker ring teeth (SRT) have emerged as a promising protein-only, thermoplastic biopolymer with an increasing number of biomedical and engineering applications demonstrated in recent years. SRT is a supra-molecular network whereby a flexible, amorphous matrix is mechanically reinforced by nanoconfined β-sheets. The building blocks for the SRT network are a family of suckerin proteins that share a common block copolymer architecture consisting of amorphous domains intervened by smaller, β-sheet forming modules. Recent studies have identified the peptide A1H1 (peptide sequence AATAVSHTTHHA) as one of the most abundant β-sheet forming domains within the suckerin protein family. However, we still have little understanding of the assembly mechanisms by which the A1H1 peptide may assemble into its functional load-bearing domains. In this study, we conduct a detailed self-assembly study of A1H1 and show that the peptide undergoes β-strands-driven elongation into amyloid-like fibrils with a rich polymorphism. The nanostructure of the fibrils was elucidated by small and wide-angle X-ray scattering (SAXS and WAXS) and atomic force microscopy (AFM). The presence of His-rich and Ala-rich segments results in an amphiphilic behavior and drives its assembly into fibrillar supramolecular chiral aggregates with helical ribbon configuration in solution, with the His-rich region exposed to the solvent molecules. Upon increase in concentration, the fibrils undergo gel formation, while preserving the same mesoscopic features. This complex phase behavior suggests that the repeat peptide modules of suckerins may be manipulated beyond their native biological environment to produce a wider variety of self-assembled amyloid-like nanostructures.

Squid Suckerin Biomimetic Peptides Form Amyloid-like Crystals with Robust Mechanical Properties.

We present the self-assembly of fibers formed from a peptide sequence (A1H1) derived from suckerin proteins of squid sucker ring teeth (SRT). SRT are protein-only biopolymers with an unconventional set of physicochemical and mechanical properties including high elastic modulus coupled with thermoplastic behavior. We have identified a conserved peptide building block from suckerins that possess the ability to assemble into materials with similar mechanical properties as the native SRT. A1H1 displays amphiphilic characteristics and self-assembles from the bottom-up into mm-scale fibers initiated by the addition of a polar aprotic solvent. A1H1 fibers are thermally resistant up to 239 °C, coupled with an elastic modulus of ∼7.7 GPa, which can be explained by the tight packing of β-sheet-enriched crystalline building blocks as identified by wide-angle X-ray scattering (WAXS), with intersheet and interstrand distances of 5.37 and 4.38 Å, respectively. A compact packing of the peptides at their Ala-rich terminals within the fibers was confirmed from molecular dynamics simulations, and we propose a hierarchical model of fiber assembly of the mature peptide fiber.

Modular peptides from the thermoplastic squid sucker ring teeth form amyloid-like cross-β supramolecular networks.

The sucker ring teeth (SRT) located on the arms and tentacles of cephalopods represent as a very promising protein-based biopolymer with the potential to rival silk in biomedical and engineering applications. SRT are made of modular, block co-polymer like proteins (suckerins), which assemble into a semicrystalline polymer reinforced by nano-confined β-sheets, resulting in a supramolecular network with mechanical properties that match those of the strongest engineering polymers. In this study, we aimed to understand the molecular mechanisms behind SRT's self-assembly and robustness. The most abundant modular peptidic blocks of suckerin proteins were studied by various spectroscopic methods, which demonstrate that SRT peptides form amyloid-like cross-β structures.

The role of water on the structure and mechanical properties of a thermoplastic natural block co-polymer from squid sucker ring teeth

Hard biological polymers exhibiting a truly thermoplastic behavior that can maintain their structural properties after processing are extremely rare and highly desirable for use in advanced technological applications such as 3D-printing, biodegradable plastics and robust composites. One exception are the thermoplastic proteins that comprise the sucker ring teeth (SRT) of the Humboldt jumbo squid (Dosidicus gigas). In this work, we explore the mechanical properties of reconstituted SRT proteins and demonstrate that the material can be re-shaped by simple processing in water and at relatively low temperature (below 100 °C). The post-processed material maintains a high modulus in the GPa range, both in the dry and the wet states. When transitioning from low to high humidity, the material properties change from brittle to ductile with an increase in plastic deformation, where water acts as a plasticizer. Using synchrotron x-ray scattering tools, we found that water mostly influences nano scale structure, whereas at the molecular level, the protein structure remains largely unaffected. Furthermore, through simultaneous in situ x-ray scattering and mechanical tests, we show that the supramolecular network of the reconstituted SRT material exhibits a progressive alignment along the strain direction, which is attributed to chain alignment of the amorphous domains of SRT proteins. The high modulus in both dry and wet states, combined with their efficient thermal processing characteristics, make the SRT proteins promising substitutes for applications traditionally reserved for petroleum-based thermoplastics.

Squid Sucker Ring Teeth: Multiscale Structure-Property Relationships, Sequencing, and Protein Engineering of a Thermoplastic Biopolymer.

The arms and tentacles of Decapodiform cephalopods (squids and cuttlefish) are lined with suckers, each of which contains embedded sucker ring teeth (SRT), which are used by the animal for prey capture and handling. SRT exhibit intriguing physicochemical and thermomechanical characteristics that have so far not been observed in other protein-based biomaterials. Notably, despite their comparatively high mechanical properties, SRT are almost fully soluble in chaotropic solvents and can be readily reconstituted after solvent evaporation into three-dimensional structures. SRT also exhibit thermoplastic characteristics: they can be melted and reshaped multiple times with no-or only minimal-loss of mechanical performance postprocessing. Intrigued by these unusual material characteristics, in recent years, we have conducted in-depth fundamental studies to unveil structure/property relationships of SRT from the molecular (genetic) level to the macroscopic scale. These investigations have demonstrated that SRT are entirely assembled from a protein family called "suckerins" that self-assemble into semicrystalline polymer infinite networks. Suckerins are block copolymers at the molecular level, whose closest analogy appears to be silk fibroins, although significant differences exist between these two protein families. Parallel to these studies, there have been efforts to mimic and engineer suckerins by protein engineering and to demonstrate potential applications through proof-of-concept studies, with a focus on the biomedical field. Both fundamental aspects and emerging applications are presented in this short review. Given the rather unusual source of this model structure, we start by a brief historical account of SRT and suckerin discovery.

Squid's Suckerin Proteins in Bits & Bytes

The suckerins or the sucker ring teeth of the Jumbo Squid are block-copolymer-like structural proteins but without a mineral phase or covalent cross-linking. Interestingly, the amino acid composition of these set of proteins are quite similar to silk proteins, that feature exceptional mechanical properties like high tensile strength and great extensibility. The tooth structure is known to assemble into a nano-confined β-sheet polymer network, interspersed within less orderly amorphous mesh-work. Remarkably, this biomaterial exhibits mechanical properties that rival those of robust bioengineered polymers.In the current work we have combined experimental and computational investigations to identify suckerin protein structure inorder to bridge the structure-function-property relationship. Our atomic detailed calculations were used to elucidate the robust supramolecular network of simple building blocks that assemble via weak hydrogen bonds ultimately leading to superior mechanical properties in squid's sucker ring teeth. In silico approach was complemented with structure based biophysical experiments for enhanced understanding of its molecular/atomic design principle.Our work sets a platform for extensive molecular level investigations of the suckerin protein family. This may contribute towards understanding the source of mechanical strength and elasticity of the protein based suckerins. It will also provide an effective template for mimicking wide range of bio-inspired materials.

From Soft Self-Healing Gels to Stiff Films in Suckerin-Based Materials Through Modulation of Crosslink Density and β-Sheet Content.

Suckerins are block-copolymer-like structural proteins constituting the building blocks of the strong squid sucker-ring teeth. Here, recombinant suckerin-19 is processed into biomaterials spanning a wide range of elasticity, from very soft hydrogels to stiff films with elastic modulus in the gigapascal range. The elasticity is controlled by the interplay between the β-sheet content and induced di-tyrosine crosslinking.

Accelerating the design of biomimetic materials by integrating RNA-seq with proteomics and materials science

Efforts to engineer new materials inspired by biological structures are hampered by the lack of genomic data from many model organisms studied in biomimetic research. Here we show that biomimetic engineering can be accelerated by integrating high-throughput RNA-seq with proteomics and advanced materials characterization. This approach can be applied to a broad range of systems, as we illustrate by investigating diverse high-performance biological materials involved in embryo protection, adhesion and predation. In one example, we rapidly engineer recombinant squid sucker ring teeth proteins into a range of structural and functional materials, including nanopatterned surfaces and photo-cross-linked films that exceed the mechanical properties of most natural and synthetic polymers. Integrating RNA-seq with proteomics and materials science facilitates the molecular characterization of natural materials and the effective translation of their molecular designs into a wide range of bio-inspired materials.