Journal of Biological Chemistry
Volume 285, Issue 49, 3 December 2010, Pages 38115-38124
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Glycobiology and Extracellular Matrices
Cross-linking Chemistry of Squid Beak*

https://doi.org/10.1074/jbc.M110.161174Get rights and content
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In stark contrast to most aggressive predators, Dosidicus gigas (jumbo squids) do not use minerals in their powerful mouthparts known as beaks. Their beaks instead consist of a highly sclerotized chitinous composite with incremental hydration from the tip to the base. We previously reported l-3,4-dihydroxyphenylalanine (dopa)-histidine (dopa-His) as an important covalent cross-link providing mechanical strengthening to the beak material. Here, we present a more complete characterization of the sclerotization chemistry and describe additional cross-links from D. gigas beak. All cross-links presented in this report share common building blocks, a family of di-, tri-, and tetra-histidine-catecholic adducts, that were separated by affinity chromatography and high performance liquid chromatography (HPLC) and identified by tandem mass spectroscopy and proton nuclear magnetic resonance (1H NMR). The data provide additional insights into the unusually high cross-link density found in mature beaks. Furthermore, we propose both a low molecular weight catechol, and peptidyl-dopa, to be sclerotization agents of squid beak. This appears to represent a new strategy for forming hard tissue in animals. The interplay between covalent cross-linking and dehydration on the graded properties of the beaks is discussed.

Histidine
Mass Spectrometry (MS)
NMR
Protein Chemistry
Protein Cross-linking
4-Methylcatechol
Biocomposite
Dosidicus gigas
Hydration
Sclerotization

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*

This work was supported, in whole or in part, by National Institutes of Health Grant R01DE018468. This work was also supported by a Nanyang Technological University start-up grant (to A. M.).

The on-line version of this article (available at http://www.jbc.org) contains Fig. S1.

2

Present address: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138.