Changes in the thermal unfolding of p-phenylenedimaleimide-modified myosin subfragment 1 induced by its 'weak' binding to F-actin.

O V Kaspieva, O P Nikolaeva, V N Orlov, M A Ponomarev, V A Drachev, D I Levitsky

Index: FEBS Lett. 489(2-3) , 144-8, (2001)

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Abstract

Differential scanning calorimetry (DSC) was used to analyze the thermal unfolding of myosin subfragment 1 (S1) with the SH1 (Cys-707) and SH2 (Cys-697) groups cross-linked by N,N'-p-phenylenedimaleimide (pPDM-S1). It has been shown that F-actin affects the thermal unfolding of pPDM-S1 only at very low ionic strength, when some part of pPDM-S1 binds weakly to F-actin, but not at higher ionic strength (200 mM KCl). The weak binding of pPDM-S1 to F-actin shifted the thermal transition of pPDM-S1 by about 5 degrees C to a higher temperature. This actin-induced increase in thermal stability of pPDM-S1 was similar to that observed with 'strong' binding of unmodified S1 to F-actin. Our results show that actin-induced structural changes revealed by DSC in the myosin head occur not only upon strong binding but also on weak binding of the head to F-actin, thus suggesting that these changes may occur before the power-stroke and play an important role in the motor function of the head.