Mathematical Biology seminar

Russell Stewart
Bioengineering Dept., University of Utah
"Foaming at the mouth: the sticky kisses of P. californica"
September 22
3:05pm in LCB 215

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 sets up through covalent crosslinking into a solid foam (closed cells) as revealed by electron and laser scanning confocal microscopy. The cement contains extractable calcium and magnesium and non-extractable phosphorous. Amino acid analysis demonstrated that the phosphorous is in the form of phosphoserine and that greater than 90% of serine in the cement, 28 mol% of residues, is phosphorylated. In addition to previously identified basic proteins (Waite et al., 1992), 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: i.) 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, ii.) 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, iii.) 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 iv.) after secretion, covalent cross-linking through oxidative coupling of DOPA gradually solidifies the continuous phase of the cement to set the porous structure.