Isotherm kinetics of PIP2 bound gelsolin inactivation

Actin monomers (G-actin) and filaments (F-actin) have dynamical rearrangement thus manage cellular motility, division and transport processes. The gelsolin (GSN) regulates the remodeling of cytoskeleton. After the activation of GSN by calcium ions, it can sever actin filaments then capped at its barbed end. In the cytoplasm, GSN manages the cellular motions and morphology. Phosphatidylinositol 4,5-bisphosphate (PIP2) is involved in signal transduction and the regulation of the actin cytoskeleton by regulation of actin-binding proteins. GSN can bind to PIP2 and thus can be localized in the near of the plasma membrane and released from the end of F-actin. We test here with isoperibol calorimetry the enthalpy change, within the interplay between GSN and F-actin under nano-, micro- and millimolar calcium concentrations and express the importance of PIP2 binding for the inactivation of GSN. As we have demonstrated here that PIP2 binding stabilizes the structure of gelsolin and reduces its actin monomer binding activity under nanomolar calcium as the typical cytoplasmic calcium concentration of resting cells. The gelsolin shows partial activity under micromolar and total activity with strong responses under millimolar calcium. If gelsolin-capped filaments point at the plasma membrane helps the binding between gelsolin and PIP2, and hence, filament uncapping in case of resting cells. We presume that the low free calcium concentration keeps on the structure of gelsolin which is able to bind actin within the cooperativity of actin bound calcium. Gelsolin can help to manage monomer pool far from the membrane and it can be linked to a basic sensory mechanism which drives the direction of filament growth in the near of the membrane.