Swank Douglas M, Kronert William A, Bernstein Sanford I, Maughan David W
Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405, USA.
Biophys J. 2004 Sep;87(3):1805-14. doi: 10.1529/biophysj.103.032078.
We assessed the influence of alternative versions of a region near the N-terminus of Drosophila myosin heavy chain on muscle mechanical properties. Previously, we exchanged N-terminal regions (encoded by alternative exon 3s) between an embryonic (EMB) isoform and the indirect flight muscle isoform (IFI) of myosin, and demonstrated that it influences solution ATPase rates and in vitro actin sliding velocity. Because each myosin is expressed in Drosophila indirect flight muscle, in the absence of other myosin isoforms, this allows for muscle mechanical and whole organism locomotion assays. We found that exchanging the flight muscle specific exon 3 region into the embryonic isoform (EMB-3b) increased maximum power generation (P(max)) and optimal frequency of power generation (f(max)) threefold and twofold compared to fibers expressing EMB, whereas exchanging the embryonic exon 3 region into the flight muscle isoform (IFI-3a) decreased P(max) and f(max) to approximately 80% of IFI fiber values. Drosophila expressing IFI-3a exhibited a reduced wing beat frequency compared to flies expressing IFI, which optimized power generation from their kinetically slowed flight muscle. However, the slower wing beat frequency resulted in a substantial loss of aerodynamic power as manifest in decreased flight performance of IFI-3a compared to IFI. Thus the N-terminal region is important in tuning myosin kinetics to match muscle speed for optimal locomotory performance.
我们评估了果蝇肌球蛋白重链N端附近区域的不同版本对肌肉力学特性的影响。此前，我们在胚胎（EMB）同工型和肌球蛋白的间接飞行肌同工型（IFI）之间交换了N端区域（由可变外显子3编码），并证明它会影响溶液中的ATP酶活性和体外肌动蛋白滑动速度。由于每种肌球蛋白都在果蝇间接飞行肌中表达，在没有其他肌球蛋白同工型的情况下，这使得我们能够进行肌肉力学和整个生物体运动测定。我们发现，与表达EMB的纤维相比，将飞行肌特异性外显子3区域交换到胚胎同工型中（EMB-3b）可使最大功率产生（P(max)）和最佳功率产生频率（f(max)）分别提高三倍和两倍，而将胚胎外显子3区域交换到飞行肌同工型中（IFI-3a）则使P(max)和f(max)降至IFI纤维值的约80%。与表达IFI的果蝇相比，表达IFI-3a的果蝇翅振频率降低，这使得它们从动力学上减慢的飞行肌中优化了功率产生。然而，较慢的翅振频率导致空气动力学功率大幅损失，这在IFI-3a与IFI相比飞行性能下降中表现明显。因此，N端区域对于调节肌球蛋白动力学以匹配肌肉速度以实现最佳运动性能很重要。
