1: Biophys J  2000 Aug;79(2):962-74 

Characterization of single actomyosin rigor bonds: load dependence of lifetime
and mechanical properties.

Nishizaka T, Seo R, Tadakuma H, Kinosita K Jr, Ishiwata S.

Department of Physics, School of Science and Engineering, Waseda University,
Tokyo 169-8555, Japan.

Load dependence of the lifetime of the rigor bonds formed between a single
myosin molecule (either heavy meromyosin, HMM, or myosin subfragment-1, S1) and
actin filament was examined in the absence of nucleotide by pulling the barbed
end of the actin filament with optical tweezers. For S1, the relationship
between the lifetime (tau) and the externally imposed load (F) at absolute
temperature T could be expressed as tau(F) = tau(0).exp(-F.d/k(B)T) with tau(0)
of 67 s and an apparent interaction distance d of 2.4 nm (k(B) is the Boltzmann
constant). The relationship for HMM was expressed by the sum of two
exponentials, with two sets of tau(0) and d being, respectively, 62 s and 2.7
nm, and 950 s and 1.4 nm. The fast component of HMM coincides with tau(F) for
S1, suggesting that the fast component corresponds to single-headed binding and
the slow component to double-headed binding. These large interaction distances,
which may be a common characteristic of motor proteins, are attributed to the
geometry for applying an external load. The pulling experiment has also allowed
direct estimation of the number of myosin molecules interacting with an actin
filament. Actin filaments tethered to a single HMM molecule underwent extensive
rotational Brownian motion, indicating a low torsional stiffness for HMM. From
these results, we discuss the characteristics of interaction between actin and
myosin, with the focus on the manner of binding of myosin.

PMID: 10920026 [PubMed - indexed for MEDLINE]