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Infiltration of chitin by protein coacervates defines the squid beak mechanical gradient.

  • Author(s): Tan, YerPeng;
  • Hoon, Shawn;
  • Guerette, Paul A;
  • Wei, Wei;
  • Ghadban, Ali;
  • Hao, Cai;
  • Miserez, Ali;
  • Waite, J Herbert
  • et al.

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.

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