Interaction sites of tropomyosin in muscle thin filament as identified by site-directed spin-labeling.

Keisuke Ueda, Chieko Kimura-Sakiyama, Tomoki Aihara, Masao Miki, Toshiaki Arata

Index: Biophys. J. 100(10) , 2432-9, (2011)

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Abstract

To identify interaction sites we measured the rotational motion of a spin label covalently bound to the side chain of a cysteine genetically incorporated into rabbit skeletal muscle tropomyosin (Tm) at positions 13, 36, 146, 160, 174, 190, 209, 230, 271, and 279. Upon the addition of F-actin, the mobility of all the spin labels, especially at position 13, 271, or 279, of Tm was inhibited significantly. Slow spin-label motion at the C-terminus (at the 230th and 271st residues) was observed upon addition of troponin. The binding of myosin-head S1 fragments without troponin immobilized Tm residues at 146, 160, 190, 209, 230, 271, and 279, suggesting that these residues are involved in a direct interaction between Tm and actin in its open state. As immobilization occurred at substoichiometric amounts of S1 binding to actin (a 1:7 molar ratio), the structural changes induced by S1 binding to one actin subunit must have propagated and influenced interaction sites over seven actin subunits.Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.