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J. Biochem, 1998, Vol. 123, No. 6 1104-1111
© 1998 Japanese Biochemical Society

research-article

Fluorescence Resonance Energy Transfer between Points on Tropomyosin and Actin in Skeletal Muscle Thin Filaments: Does Tropomyosin Move?1

Masao Miki*,2, Tomoo Miura*, Ken-Ichi Sano{dagger}, Hiroyuki Kimura*, Hiroyuki Kondo*, Hiroshi Ishida* and Yuichiro Maéda{dagger}

*Department of Applied Chemistry and BioTechnology, Fukui University 3-9-1 Bunkyo, Fukui 910-8507
{dagger}International Institute for Advanced Research, Matsushita Electric Industrial Co., Ltd. 3-4 Hikaridai, Seika 619-02

2To whom correspondence should be addressed. Tel: +81-776-27-8786, Fax: +81-776-27-8747, E-mail: masao{at}acbio.fukui-u.ac.jp

Fluorescence resonance energy transfer (FRET) spectroscopy has been used to determine spatial relationships between residues on tropomyosin and actin in reconstituted muscle thin filament, and to detect a positional change of tropomyosin relative to actin on the thin filament in the presence and absence of Ca2+ ions. In addition to Cys-190 which is a single cysteine residue in rabbit skeletal muscle {alpha}-tropomyosin, a new site, Cys-87 which is a unique cysteine residue in a mutant {alpha}-tropomyosin, was labeled with a resonance energy donor molecule, 5-(2-iodoacetylaminoethyl)aminonaphthalene 1-sulfonic acid (IAED-ANS). On the other hand, Gln-41, Lys-61, Cys-374, and the ATP-binding site of actin were selectively labeled with acceptor probes: fluorescein cadaverine, fluorescein 5-isothiocyanate, 4-dimethyl-aminophenylazophenyl 4'-maleimide, and TNP-ATP (or TNP-ADP), respectively. The distances between probes attached to position 87 of the mutant tropomyosin and Gln-41, Lys-61, Cys-374, or the nucleotide-binding site of actin on the reconstituted thin filament in the presence of Ca2+ ion were measured to be 43.2, 49.7, 45.4, and 35.2 A, respectively, and the distance between probes attached to position 190 of tropomyosin and Gln-41 or the nucleotide-binding site of actin were 51.6 and 43.1 Å, respectively. The transfer efficiencies between these donor and acceptor molecules were large, so that the efficiency should be very sensitive to changes in distance between probes attached to tropomyosin and actin. However, the transfer efficiency did not change appreciably upon removal of Ca2+ ions, suggesting that tropomyosin does not change its position on the reconstituted thin filament in response to a change in Ca2+ ion concentration. The present results do not support the notion of tropomyosin movement on skeletal muscle thin filaments as proposed in the steric blocking theory.

1This work was partially supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan.


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M. Miki, H. Hai, K. Saeki, Y. Shitaka, K.-I. Sano, Y. Maeda, and T. Wakabayashi
Fluorescence Resonance Energy Transfer between Points on Actin and the C-Terminal Region of Tropomyosin in Skeletal Muscle Thin Filaments
J. Biochem., July 1, 2004; 136(1): 39 - 47.
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