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Open Access Publications from the University of California

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

  • Author(s): Tan, Y
  • Hoon, S
  • Guerette, PA
  • Wei, W
  • Ghadban, A
  • Hao, C
  • Miserez, A
  • Waite, JH
  • et al.

© 2015 Nature America, Inc. All rights reserved. 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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