Nanoconfined β-Sheets Mechanically Reinforce the Supra-Biomolecular Network of Robust Squid Sucker Ring Teeth

Abstract

The predatory efficiency of squid and cuttlefish (superorder Decapodiformes) is enhanced by robust Sucker Ring Teeth (SRT) that perform grappling functions during prey capture. Here, we show that SRT are composed entirely of related structural “suckerin” proteins whose modular designs enable the formation of nanoconfined β-sheet-reinforced polymer networks. Thirty-seven previously undiscovered suckerins were identified from transcriptomes assembled from three distantly related decapodiform cephalopods. Similarity in modular sequence design and exon–intron architecture suggests that suckerins are encoded by a multigene family. Phylogenetic analysis supports this view, revealing that suckerin genes originated in a common ancestor ~350 MYa and indicating that nanoconfined β-sheet reinforcement is an ancient strategy to create robust bulk biomaterials. X-ray diffraction, nanomechanical, and micro-Raman spectroscopy measurements confirm that the modular design of the suckerins facilitates the formation of β-sheets of precise nanoscale dimensions and enables their assembly into structurally robust supramolecular networks stabilized by cooperative hydrogen bonding. The suckerin gene family has likely played a key role in the evolutionary success of decapodiform cephalopods and provides a large molecular toolbox for biomimetic materials engineering.

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

“…Based on the experimental evidence that suckerin peptides self-assemble into β-sheet rich fibrillar structures with a high structural stability, and with our previous understanding that native SRT are semi-crystalline biopolymers in which nanoconfined β-sheets [8] represents the crystalline phase, a plausible structure for the SRT peptides investigated in this study can be proposed. Accordingly, the peptides are stacked into anti-parallel β-strands, with the strands oriented perpendicular to the fibrils axis and hydrogen bonds parallel to the fibril axis, namely the classical cross-β structure observed in amyloid fibrils.…”

“…[8] We further refined the selection of peptides based on recent Wide-Angle X-ray Scattering (WAXS) synchrotron experiments of native SRT, which revealed the existence of a network of nano-confined β-sheet structures with dimensions of 2.4-2.6 nm by 3-3.5 8 nm (estimated 5 strands of ~8-10 residues) [4,8] that were arranged isotropically within an amorphous matrix. Based on the β-sheet forming propensities of amino acids and the well-known formation of β-sheets in spider dragline silks arising from poly-Ala sequences, [23] we hypothesized that the combination of Ala-and His-rich domains were the likely source of β strands in the nano-confined β-sheet reinforced polymer network.…”

“…[7] We have previously sequenced dozens of genes encoding members of the suckerin protein family. [8] The suckerins are highly repetitive and modular, and assemble into a semi-crystalline supramolecular network consisting of an amorphous matrix reinforced with nano-confined β-sheets. [4,8,9] Almost all suckerins consist of peptide motifs that are reminiscent to those found in silk proteins.…”

“…We dissected the primary amino acid sequence of the most abundant suckerin protein, suckerin-19 (molecular weight 39kDa, Figure 1A) to identify the key modular units and explore their fundamental interactions at the molecular scale. Importantly, the modular peptides found in suckerin-19 are conserved within most other members of the suckerin gene family, [8] allowing us to investigate peptide sequence designs that are relevant to the entire SRT system. A combinatorial peptide macroarray interaction assay was first designed to map out the interactions between the modular peptides, which was assessed by fluorescence intensity, whereas dynamic light scattering (DLS) experiments were used to monitor the kinetics of peptide self-assembly.…”

Structural, Nanomechanical, and Computational Characterization of d,l-Cyclic Peptide Assemblies

“…Indeed, the properties exceed those of amyloid fibrils and are on par with those of silks, suckerins, 40,41 and diphenylalanine nanotubes, 42 the most robust known self-assembling peptide based materials. Furthermore, they maintain those properties even at the micron length scale.…”