Key result
S1-induced polymerization of G-actin involves the rapid formation of G-actin-S1 oligomers with a 2:1 molar ratio, an endothermic process with a delta H of 14 kcal/mol.
The study characterizes the kinetic intermediates in S1-induced polymerization of G-actin, proposing a model where longitudinal actin-actin interactions occur in G2S complexes followed by lateral hydrophobic interactions in oligomers.
No clinical implications from this animal study; leaves open validation of the G-actin oligomer model in vivo.
The nature of the kinetic intermediates involved in S1-induced polymerization of G-actin into F-acto-S1-decorated filaments has been investigated using as probes light scattering, the fluorescence of pyrenyl- or NBD-labeled actin, and the anisotropy of fluorescence of N-iodoacetyl-N'-(5-sulfo-1-napthyl)ethylene diamine (AEDANS)-labeled actin. With AEDANS-G-actin, the initial formation of a ternary G2S complex between two G-actin and one S1 molecules (Valentin-Ranc, C., Combeau, C., Carlier, M. F., and Pantaloni, D. (1991) J. Biol. Chem. 266, 17871-17879) has been confirmed. Data obtained with all probes are consistent with the subsequent rapid formation of G-actin-S1 oligomers in which the actin/S1 molar ratio is 2:1. Oligomers form above 0.6 microM G-actin with S1(A1) and above 3.5 microM G-actin with S1(A2), at 20 degrees C. Oligomerization is endothermic with a delta H of 14 kcal/mol. A tentative model is proposed to comprehensively account for the data and the structural features of the F-actin-S1 filament. Within this model, longitudinal actin-actin interactions take place in G2S, and lateral, hydrophobic actin-actin interactions appear upon formation of (G2S)n oligomers.
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Valentin-Ranc et al. (1992) studied this question. Myosin subfragment 1 (S1) was evaluated on Kinetic intermediates in S1-induced polymerization of G-actin. S1-induced polymerization of G-actin involves the rapid formation of G-actin-S1 oligomers with a 2:1 molar ratio, an endothermic process with a delta H of 14 kcal/mol.
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