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Calcium mediated cooperative adhesion plays an important role in biological cell adhesion. We investigated the Ca2+-dependent interaction of the complete aggregation factors of a marine sponge as well as its homophilic carbohydrate g200 self-recognition element with AFM single molecule force spectroscopy (AFMFS) [1].
A detailed analysis of the single molecule g200-g200 AFMFS interaction data in the presence and the absence of Ca2+ indicate a moderate dependence of bond lifetime and bond reaction length on calcium concentration, respectively. But the measured difference at the single molecule level does not account for the observed macroscopic properties with respect of the whole sponge integrity. However, a more subtle stochastic cluster dynamics analysis within the framework of a cooperative binding model [2] can explain the nonlinear and divergent Ca2+-dependent adhesion characteristics leading to either disaggregated cells or stable multicellular assemblies, respectively. Since these simply organized sponge organisms were among the first multicellular organisms and survived the last 500 Mio. years phenotypically almost unchanged, they are considered as a link between the single cell dominated precambrium and the multicellular postarea. In this respect, the observed calcium-dependent cooperative binding phenomenon can explain the transition from weak to strong adhesion between primitive metazoan cells. Especially in the light of the well-documented massive rise in ocean calcium levels at the end of precambrian time - that is believed to be the result of volcanically active midocean ridges, not only initiated the builtup of calcified bones and shells, but was also mandatory for the aggregation and stabilisation of multicellular sponge structures. This allows, on the other hand, to formulate a novel theory where the geologically induced increase on marine calcium might be the key for understanding the Cambrian Explosion of Life.
[1] X. Fernandez-Busquets, A. Körnig, I. Bucior, M. M. Burger, and D. Anselmetti, Self-Recognition and Ca-Dependent Carbohydrate-Carbohydrate Cell Adhesion Provide Clues to the Cambrian Explosion, Molecular Biology and Evolution, in press (2009). [2] T. Erdmann, U.S. Schwarz, Stochastic dynamics of adhesion clusters under shared constant force and with rebinding, J. Chem. Phys. 121:8997-9017 (2004) and T. Erdmann and U. S. Schwarz, Stability of Adhesion Clusters under Constant Force, Phys. Rev. Lett. 92, 108102 (2004). |
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