The tube cement of Phragmatopoma californica: a solid foam.
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.
Stewart
Russell J
RJ
Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, USA.
Weaver
James C
JC
Morse
Daniel E
DE
Waite
J Herbert
JH
D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D002118:Calcium / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D004295:Dihydroxyphenylalanine / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D010768:Phosphoserine / Q000737:chemistry; D011077:Polychaeta / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry* / Q000648:ultrastructure; D055672:Static Electricity
D000596:Amino Acids; D011506:Proteins; D010768:Phosphoserine; D004295:Dihydroxyphenylalanine; D008274:Magnesium; D002118:Calcium