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

TitleInfiltration of chitin by protein coacervates defines the squid beak mechanical gradient.
Publication TypeJournal Article
Year of Publication2015
AuthorsTan, Y, Hoon, S, Guerette, PA, Wei, W, Ghadban, A, Hao, C, Miserez, A, Waite, JH
JournalNat Chem Biol
Date Published2015 Jul
KeywordsAmino Acid Sequence, Animals, Beak, Biomechanical Phenomena, Catechols, Chitin, Cross-Linking Reagents, Decapodiformes, Hardness, Molecular Sequence Data, Periodic Acid, Protein Binding, Protein Structure, Tertiary, Proteins, Proteomics, Sequence Analysis, RNA, Water

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.

Alternate JournalNat. Chem. Biol.
PubMed ID26053298
Grant ListR01-DE018468 / DE / NIDCR NIH HHS / United States