Mechanisms Controlling the Super-Relaxed State

描述（由申请人提供）：我们最近的工作已经在ATP周转率非常慢的放松肌肉中发现了一种新的肌球蛋白状态，即“超放松状态”（SRX）。在骨骼肌中，SRX被认为在决定静息肌肉的产热作用中起作用。在心室肌中，SRX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被认为是通过在应激时有效地降低心脏代谢来发挥心脏保护作用。我们也证明了平滑肌有非常稳定的SRX。最近的研究也表明，在狼蛛肌肉中，SRX的持续时间很长，这与之前的EM数据一致。拟议研究的目标将是确定调节SRX的因素，特别是在骨骼、心脏和平滑肌中。我们已经证明SRX的种群是由快速骨骼肌和狼蛛腿肌中的RLC磷酸化调节的。我们将把这些研究扩展到慢骨骼肌、心肌和平滑肌。肌球蛋白磷酸化发生在慢骨骼肌；然而，其功能尚不清楚。本研究将探讨其在控制SRX和静息产热中的可能作用。在心肌中，肌球蛋白的磷酸化引起张力增加。我们最近的工作表明SRX在心脏中的作用是调节张力，我们将探索肌球蛋白磷酸化、SRX的数量和肌肉张力之间的关系。对活的、静止的骨骼肌和心肌的观察表明，疲劳和缺氧使新陈代谢急剧下降。SRX中大量的肌球蛋白是达到静止骨骼肌中非常低的代谢率的必要条件，我们也提出在心脏中也是如此。因此，我们将探讨模拟疲劳和缺氧条件对SRX的影响。研究将扩展到平滑肌，磷酸化也调节功能。这些数据将被SRX的结构研究补充，使用EPR探针来监测粗丝的结构和核苷酸口袋的构象。初步数据表明，核苷酸自旋探针可以报告粗丝的有序结构。在与Roger Craig的合作中，光谱探针将提供数据，并在相同的条件下（磷酸化、疲劳/缺氧等条件）结合EM可视化来探索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知识。这些研究将提供许多基础生物学知识，这些知识的理解将是我们追求长期目标所必需的，即开发SRX在治疗人类健康问题方面的许多明显应用。减少静息骨骼肌中SRX的数量可以增加肌肉和全身代谢，为治疗肥胖和2型糖尿病提供新的治疗方法。增加静息和活动心肌中SRX的数量可以降低代谢率，起到保护心脏的作用。

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.