Theoretical Characterization of the Long-range Attraction between G-actin Molecules through the Excluded Volume Effect.

One of the interactions between macromolecules is the attractive forcethrough the excluded volume effect. We studied the attraction betweenthe molecules of muscle protein, actin, in the two points by using theextended scaled particle theory (XSPT). I) we verified the basic assumptionused in the XSPT that topological elements which determine the analyticalexpression of the excluded volume are almost unchanged through the scalingdown of the solute molecule in the thought experiment. Results of thecomputational geometry method (α-shape method) showed that thisassumption is valid even in the case of the actin molecule. II) wecalculated the attraction between actin monomer molecules, G-actin.Calculated differences of the values of the attraction potential of twomacromolecules between at contact and at one macromolecule apart by theXSPT is almost the same as those by the Asakura-Oosawa theory.