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First published online December 3, 2004
Journal of Experimental Biology 207, 4727-4734 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01330

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The tube cement of Phragmatopoma californica: a solid foam

Russell J. Stewart¹, James C. Weaver², Daniel E. Morse³ and J. Herbert Waite^3,*

¹ Department of Bioengineering, University of Utah, Salt Lake City, UT 84112
² Institute for Collaborative Biotechnologies and the Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA
³ Marine Science Institute and MCDB Department, University of California, Santa Barbara, CA 93106, USA

^* Author for correspondence (e-mail: waite{at}lifesci.ucsb.edu)

Accepted 11 October 2004

Phragmatopoma californica is a marine polychaete that builds protective tubes by joining bits of shell and sand grains with a secreted proteinaceous cement. The cement forms a solid foam (closed cells) via covalent crosslinking, as revealed by electron and laser scanning confocal microscopy. The cement contains extractable calcium and magnesium, and non-extractable phosphorus. Amino acid analysis demonstrated that the phosphorus is in the form of phosphoserine and that >90% of serine in the cement (i.e. 28 mol% of residues) is phosphorylated. In addition to previously identified basic proteins, the cement contains a highly acidic polyphosphoserine protein as a major component. We propose a model for the structure and bonding mechanism of the cement that has the following major features: (1) within the secretory pathway of cement gland cells, the electrostatic association of the oppositely charged proteins and divalent cations (Ca²⁺ and Mg²⁺) condense the cement proteins into dehydrated secretory granules; (2) the condensation of the cement leads to the separation of the solution into two aqueous phases (complex coacervation) that creates the closed cell foam structure of the cement; (3) rehydration of the condensed cement granules after deposition onto tube particles contributes to the displacement of water from the mineral substrate to facilitate underwater adhesion; and (4) after secretion, covalent cross-linking through oxidative coupling of DOPA gradually solidifies the continuous phase of the cement to set the porous structure.

Key words: polychaeta, sabellariidae, Phragmatopoma californica, bioadhesion, complex coacervation, polyphosphoserine

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