Mechanisms Controlling the Super-Relaxed State

描述（由申请人提供）：我们最近的工作已经确定了松弛肌肉中肌球蛋白的一种新状态，其 ATP 周转率非常慢，即“超松弛状态”(SRX)。在骨骼肌中，SRX 被认为在确定静息肌肉的生热作用中发挥着作用。在心室肌中，它与骨骼肌中的 SRX 有许多相似之处，但也有一些重要的区别，SRX 被认为通过在应激时有效降低心脏代谢来发挥心脏保护作用。我们还表明平滑肌具有非常稳定的 SRX。最近的研究还表明，在狼蛛肌肉中，SRX 的持续时间非常长，这与之前的 EM 数据一致。拟议研究的目标是确定调节 SRX 的因素，特别是在骨骼肌、心脏和平滑肌中。我们已经证明，快速骨骼肌和狼蛛腿部肌肉中的 SRX 群体受到 RLC 磷酸化的调节。我们将把这些研究扩展到减缓骨骼肌、心脏和平滑肌。肌球蛋白的磷酸化发生在慢速骨骼肌中；但其功能仍然未知。拟议的研究将探索在控制 SRX 和静息产热方面的可能作用。在心肌中，肌球蛋白的磷酸化会导致张力增加。我们最近的工作表明，SRX 在心脏中的作用是调节张力，我们将探讨肌球蛋白磷酸化、SRX 数量和肌肉张力之间的关系。对活体、静息骨骼肌和心肌的观察表明，疲劳和缺氧会显着降低新陈代谢。 SRX 中的大量肌球蛋白是实现静息骨骼肌中极低代谢率的必要条件，我们建议在心脏中也是如此。因此，我们将探讨模拟疲劳和缺氧的条件对 SRX 的影响。这些研究将扩展到平滑肌，其中磷酸化也调节功能。这些数据将得到使用 EPR 探针监测粗丝结构和核苷酸口袋构象的 SRX 结构研究的补充。初步数据表明核苷酸自旋探针可以报告粗丝的有序结构。与 Roger Craig 合作，光谱探针将提供数据，这些数据将在相同条件（磷酸化、疲劳/缺氧条件等）下与 ​​EM 可视化相结合，以探索 SRX 的结构。这些研究将极大地扩展我们对这种新发现的肌球蛋白状态的非常有限的了解。这些研究将提供许多基础生物学知识，我们需要了解这些基础生物学知识来实现​​我们的长期目标，即开发 SRX 治疗人类健康问题的许多明显应用。减少静息骨骼肌中 SRX 的数量可以增加肌肉和全身的新陈代谢，为治疗肥胖和 2 型糖尿病提供一种新疗法。增加静息和活动心肌中 SRX 的数量可以降低代谢率，从而提供心脏保护作用。

DESCRIPTION (provided by applicant): Our recent work has identified a new state of myosin in relaxed muscle with a very slow ATP turnover rate, the "super-relaxed state" (SRX). In skeletal muscle the SRX is proposed to play a role in determining thermogenesis by resting muscle. In cardiac ventricular muscle, where it has many similarities, but some important differences with the SRX in skeletal muscle, the SRX is proposed to play a cardio-protective role by efficiently de- creasing cardiac metabolism in times of stress. We have also shown that smooth muscle has a very stable SRX. Recent work has also demonstrated that in tarantula muscle the SRX has a very long duration, in agreement with previous EM data. The goal of the proposed research will be to determine the factors that modulate the SRX, particularly in skeletal, cardiac and smooth muscles. We have shown that the population of the SRX is modulated by RLC phosphorylation in fast skeletal muscle and in tarantula leg muscle. We will expand these studies to slow skeletal, cardiac and smooth muscles. Phosphorylation of myosin occurs in slow skeletal muscle; however its function remains unknown. The proposed research will explore a possible role in controlling the SRX and resting thermogenesis. In cardiac muscle, phosphorylation of myosin causes increased tension. Our recent work suggests that a role of the SRX in cardiac is to modulate tension, and we will explore the relationship between myosin phosphorylation, the population of the SRX and muscle tension. Observations in living, resting skeletal and cardiac muscle show that metabolism is dramatically decreased by fatigue and hypoxia. A high population of myosin in the SRX is a requirement for achieving the very low metabolic rate seen in resting skeletal muscle, and we propose also in cardiac. Thus we will explore the effect of conditions that mimic fatigue and hypoxia on the SRX. The studies will be extended to smooth muscle where phosphorylation also modulates function. These data will be complimented by structural studies of the SRX using EPR probes to monitor the structure of the thick filament and the conformation of the nucleotide pocket. Preliminary data suggest that nucleotide spin probes can report on the ordered structure of the thick filament. In collaboration with Roger Craig, spectroscopic probes will provide data that will be combined with EM visualization under identical conditions (phosphorylation, conditions of fatigue/hypoxia, etc.) to explore the structure of the SRX. These studies will vastly expand our very limited knowledge of this newly identified state of myosin. The studies will provide much of the fundamental biology whose understanding will be required to pursue our long-term goal, the development of the many obvious applications of the SRX for treating human health problems. Decreasing the population of the SRX in resting skeletal muscle could increase both muscle and whole body metabolism providing a new therapy for treating obesity and type 2 diabetes. Increasing the population of the SRX in resting and active cardiac muscle could lower the metabolic rate providing cardioprotection.