Visualizing Temperature Mediated Activation of Gelsolin and Its Deactivation By Pip(2): A Saxs Based Study

This is the first report describing temperature based initiation of gelsolin’s F-actin depolymerization activity, even in absence of free Ca(2+) or low pH. Small angle X-ray scattering (SAXS) and circular dichroism (CD) studies revealed that temperature in the range of 30–40 °C is capable of opening the G1 domain alone, as remaining domains are held together by the Ca(2+)-sensitive C-tail latch without any loss in the secondary structural content. Full opening of all domains of tail-less gelsolin, and retention of closed shape for G2–G6 gelsolin merely by heating, further substantiated our findings. The Ca(2+)/pH independent activity of gelsolin near physiological temperature brought out a query: whether gelsolin is always active, and if not, what might deactivate it? Earlier, PIP(2) has been reported to render gelsolin inactive with no structural insight. Reduction in shape parameters and modeling revealed that PIP(2) reverses the temperature induced extension of g1-g2 linker leading to a compact shape seen for Ca(2+)-free gelsolin. Similar results for partially activated gelsolin (by low pH or Ca(2+) ions below 0.1 μM) imply that inside cells, depolymerization, capping, and nucleation of F-actin by gelsolin is regulated by the culmination of local Ca(2+) ion concentration, pH, temperature and PIP(2) levels.