title: Infiltration of chitin by protein coacervates defines the squid beak mechanical gradient.
abstract: 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.
authors.affiliation: Biomolecular Science and Engineering Program, University of California, Santa Barbara, California, USA.
authors.forename: YerPeng
authors.initials: Y
authors.lastname: Tan
authors.affiliation: 1] Molecular Engineering Lab, Biomedical Sciences Institutes, Agency for Science, Technology and Research (A*STAR), Singapore. [2] School of Biological Sciences, Nanyang Technological University, Singapore.
authors.forename: Shawn
authors.initials: S
authors.lastname: Hoon
authors.affiliation: 1] Energy Research Institute at Nanyang Technological University (ERI@N), Nanyang Technological University, Singapore. [2] Biological &Biomimetic Material Laboratory, School of Materials Science &Engineering, Nanyang Technological University, Singapore.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Guerette
authors.affiliation: Materials Research Laboratory, University of California, Santa Barbara, California, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Wei
authors.affiliation: Biological &Biomimetic Material Laboratory, School of Materials Science &Engineering, Nanyang Technological University, Singapore.
authors.forename: Ali
authors.initials: A
authors.lastname: Ghadban
authors.affiliation: Biological &Biomimetic Material Laboratory, School of Materials Science &Engineering, Nanyang Technological University, Singapore.
authors.forename: Cai
authors.initials: C
authors.lastname: Hao
authors.affiliation: 1] School of Biological Sciences, Nanyang Technological University, Singapore. [2] Biological &Biomimetic Material Laboratory, School of Materials Science &Engineering, Nanyang Technological University, Singapore.
authors.forename: Ali
authors.initials: A
authors.lastname: Miserez
authors.affiliation: 1] Biomolecular Science and Engineering Program, University of California, Santa Barbara, California, USA. [2] Materials Research Laboratory, University of California, Santa Barbara, California, USA. [3] Department of Molecular Cellular and Developmental Biology, University of California, Santa Barbara, California, USA.
authors.forename: J Herbert
authors.initials: JH
authors.lastname: Waite
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001502:Beak / Q000737:chemistry* / Q000378:metabolism; D001696:Biomechanical Phenomena; D002396:Catechols / Q000737:chemistry; D002686:Chitin / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D003432:Cross-Linking Reagents / Q000737:chemistry; D049832:Decapodiformes / Q000737:chemistry* / Q000378:metabolism; D006244:Hardness; D008969:Molecular Sequence Data; D010504:Periodic Acid / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D040901:Proteomics; D017423:Sequence Analysis, RNA; D014867:Water / Q000737:chemistry*; D000099053:Histidine-Rich Glycoprotein
chemical_list: D002396:Catechols; D003432:Cross-Linking Reagents; D011506:Proteins; D000099053:Histidine-Rich Glycoprotein; D014867:Water; D010504:Periodic Acid; C018599:4-methylcatechol; D002686:Chitin; C009288:metaperiodate