Conformational change of skeletal muscle α-actinin induced by salt

Abstract

We examined the effect of KCl concentration on conformation of skeletal muscle α-actinin. One-dimensional peptide maps of α-actinin digested with chymotrypsin indicated that α-actinin can take on at least three different conformations depending on the KCl concentration of the solvent, i.e., at low (0–0.02 M KCl), intermediate (0.05–0.2 M KCl), and high (0.3–0.6 M KCl) salt concentration. Viscosity measurement and gel-filtration chromatography of α-actinin at these three salt ranges indicated that the axial ratio of α-actinin increased as the ionic strength of the solvent decreased. By assuming 45% hydration of the α-actinin molecule and using a molecular weight of 210000, dimensions of α-actinin were calculated from viscosity data. The size estimated under the low-salt conditions was 3.2 × 74.2 nm. They were 3.4 × 51.3 nm and 4.5 × 40.1 nm, respectively, in the intermediate and high salt ranges. The result of the gel-filtration chromatography showed that the conformational change was reversible and that the change took place through the elongation and/or shortening of the rod domain of the molecule. We explain the salt-induced length change of α-actinin by the twisted-coiling model proposed by McGough and Josephs for erythrocyte spectrin (McGough, A. and Josephs, R. (1990) Proc. Natl. Acad. Sci. USA 87, 5208–5212). Pelleting experiments indicated that the conformational change affected the binding ratio between α-actinin and actin.