Dissociative Mechanism of F-Actin Thermal Denaturation

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V. V. Mikhailova¹, B. I. Kurganov¹, A. V. Pivovarova^1,2, and D. I. Levitsky^1,3*

¹Bach Institute of Biochemistry, Russian Academy of Sciences, Leninsky pr. 33, 119071 Moscow, Russia; fax: (495) 954-2732; E-mail: levitsky@inbi.ras.ru

²Faculty of Bioengineering and Bioinformatics and ³Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia

^* To whom correspondence should be addressed.

Received April 24, 2006; Revision received May 18, 2006

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We have applied differential scanning calorimetry to investigate thermal unfolding of F-actin. It has been shown that the thermal stability of F-actin strongly depends on ADP concentration. The transition temperature, T_m, increases with increasing ADP concentration up to 1 mM. The T_m value also depends on the concentration of F-actin: it increases by almost 3°C as the F-actin concentration is increased from 0.5 to 2.0 mg/ml. Similar dependence of the T_m value on protein concentration was demonstrated for F-actin stabilized by phalloidin, whereas it was much less pronounced in the presence of AlF₄^-. However, T_m was independent of protein concentration in the case of monomeric G-actin. The results suggest that at least two reversible stages precede irreversible thermal denaturation of F-actin; one of them is dissociation of ADP from actin subunits, and another is dissociation of subunits from the ends of actin filaments. The model explains why unfolding of F-actin depends on both ADP and protein concentration.

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KEY WORDS: actin, thermal denaturation, differential scanning calorimetry

DOI: 10.1134/S0006297906110125

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