Bach Institute of Biochemistry, Russian Academy of Sciences.
Acta Naturae. 2010 Jul;2(2):77-82.
We compared the thermal aggregation properties of two isoforms of the isolated myosin head (myosin subfragment 1, S1) containing different "essential" (or "alkali") light chains, A1 or A2. Temperature dependencies for the aggregation of these two S1 isoforms, as measured by the increase in turbidity, were compared with the temperature dependencies of their thermal denaturation obtained from differential scanning calorimetry (DSC) experiments. At relatively high ionic strength (in the presence of 100 mM KCl) close to its physiological values in muscle fibers, we have found no appreciable difference between the two S1 isoforms in their thermally induced aggregation. Under these conditions, the aggregation of both S1 isoforms was independent of the protein concentration and resulted from their irreversible denaturation, which led to the cohesion of denatured S1 molecules. In contrast, a significant difference between these S1 isoforms was revealed in their aggregation measured at low ionic strength. Under these conditions, the aggregation of S1 containing a light chain A1 (but not A2) was strongly dependent on protein concentration, the increase of which (from 0.125 to 2.0 mg/ml) shifted the aggregation curve by ~10 degrees towards the lower temperatures. It has been concluded that the aggregation properties of this S1 isoform at low ionic strength is basically determined by intermolecular interactions of the N-terminal extension of the A1 light chain (which is absent in the A2 light chain) with other S1 molecules. These interactions seem to be independent of the S1 thermal denaturation, and they may take place even at low temperature.
我们比较了两种分离肌球蛋白头部（肌球蛋白亚基 1，S1）的同型异构体的热聚集性质，它们含有不同的“必需”（或“碱性”）轻链 A1 或 A2。通过浊度增加来测量这两种 S1 同型异构体的聚集温度依赖性，并将其与从差示扫描量热法（DSC）实验获得的热变性温度依赖性进行比较。在相对较高的离子强度（存在 100mM KCl）下，接近肌肉纤维中的生理值，我们没有发现两种 S1 同型异构体在热诱导聚集方面有明显差异。在这些条件下，两种 S1 同型异构体的聚集都与蛋白质浓度无关，并且是由于它们的不可逆变性导致变性 S1 分子的凝聚。相比之下，在低离子强度下测量的这些 S1 同型异构体的聚集之间存在显著差异。在这些条件下，含有轻链 A1 的 S1（而不是 A2）的聚集强烈依赖于蛋白质浓度，其浓度的增加（从 0.125 到 2.0mg/ml）将聚集曲线向较低温度移动约 10 度。结论是，在低离子强度下，这种 S1 同型异构体的聚集性质基本上由 A1 轻链的 N 端延伸（在 A2 轻链中不存在）与其他 S1 分子之间的分子间相互作用决定。这些相互作用似乎独立于 S1 的热变性，并且即使在低温下也可能发生。
