Key result
Myosin subfragment 1 isoforms A1 and A2 showed no appreciable difference in aggregation properties under ionic strength conditions close to those in the muscle fiber.
The study identifies the motor and regulatory domains of the myosin head using differential scanning calorimetry and shows that aggregation kinetics are limited by irreversible denaturation of the motor domain, independent of the essential light chain isoform.
Motor domain denaturation limits myosin aggregation independent of isoform; leaves open isoform roles in human muscle disease.
We compared thermally induced denaturation and aggregation of two isoforms of the isolated myosin head (myosin subfragment 1, S1) containing different "essential" (or "alkali") light chains, A1 or A2. We applied differential scanning calorimetry (DSC) to investigate the domain structure of these two S1 isoforms. For this purpose, a special calorimetric approach was developed to analyze the DSC profiles of irreversibly denaturing multidomain proteins. Using this approach, we revealed two calorimetric domains in the S1 molecule, the more thermostable domain denaturing in two steps. Comparing the DSC data with temperature dependences of intrinsic fluorescence parameters and S1 ATPase inactivation, we have identified these two calorimetric domains as motor domain and regulatory domain of the myosin head, the motor domain being more thermostable. Some difference between the two S1 isoforms was only revealed by DSC in thermal denaturation of the regulatory domain. We also applied dynamic light scattering (DLS) to analyze the aggregation of S1 isoforms induced by their thermal denaturation. We have found no appreciable difference between these S1 isoforms in their aggregation properties under ionic strength conditions close to those in the muscle fiber (in the presence of 100 mM KCl). Under these conditions kinetics of this process was independent of protein concentration, and the aggregation rate was limited by irreversible denaturation of the S1 motor domain.
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Markov et al. (2010) studied this question. Myosin subfragment 1 isoforms (A1 vs A2) was evaluated on Thermal denaturation and aggregation. Myosin subfragment 1 isoforms A1 and A2 showed no appreciable difference in aggregation properties under ionic strength conditions close to those in the muscle fiber.