Open AccessThe First Step in the Polymerisation of Actin
Author(s) -
ROUAYRENC JeanFrançois,
TRAVERS Franck
Publication year - 1981
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1981.tb05302.x
Subject(s) - actin , polymerization , monomer , chemistry , conformational change , proteolysis , actin binding protein , biophysics , crystallography , biochemistry , actin cytoskeleton , polymer , biology , cytoskeleton , organic chemistry , enzyme , cell
In the presence of certain cations (e.g. K + or Mg 2+ ) actin polymerizes. Below a certain concentration (the critical concentration) the monomer G‐actin does not polymerize on the addition of K + or Mg 2+ . However, the proteolysis experiments of Rich and Estes [ J. Mol. Biol. 104 , 777–792 (1976)] strongly suggest that cations induce a change in conformation of G‐actin leading to a novel form of actin, G * ‐actin. This conformational change may be the first step in the polymerization of actin. We have studied G * ‐actin induced by K + , by difference spectroscopy. We show that G * ‐actin is a monomer and we confirm that the bound ATP is not cleaved. We also studied the G‐actin—G * ‐actin equilibrium at 4 °C as a function of K + or Mg 2+ concentration. With KCl, the transformation can be accounted for as a screening effect. The effect of Mg 2+ , is more specific and the chance in conformation of the G‐actin could result from the binding of two or three Mg 2+ ions/molecule. We suggest that the G‐actin—G * ‐actin transformation results from the neutralization of a polyanionic region on the actin surface and that this region could be the highly negatively charged N terminus.