Myosin-binding protein C stabilizes, but is not the sole determinant of SRX myosin in cardiac muscle.
Myosin-binding protein C stabilizes, but is not the sole determinant of SRX myosin in cardiac muscle.
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DOI：
10.1085/jgp.202213276
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发表时间：
2023-04-03
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横纹肌的功能调节是通过将肌球蛋白隔离到超放松（SRX）状态来实现的。观察心肌肌瘤内单个ATP分子的周转，确定了SRX肌球蛋白的空间排列及其受肌球蛋白结合蛋白c的调节。肌球蛋白超放松（SRX）状态是横纹肌代谢和功能调节的核心。在骨骼肌中，SRX肌球蛋白主要与肌球蛋白结合蛋白C （MyBP-C）在肌节C区共定位。为了确定心肌MyBP-C （cMyBP-C）及其特定结构域如何有助于稳定心肌的SRX状态，我们利用转基因cMyBP-C缺失小鼠和表达n端截断271个残基的cMyBP-C的小鼠。利用超分辨率显微镜，我们确定了在分离的心肌原纤维中单个荧光atp转换事件的寿命和肌下位置。SRX肌球蛋白的比例沿半粗丝呈梯度分布，P区和c区最高（分别为72±9%和71±6%），d区较低（45±10%），d区离肌节中心较远，缺乏cMyBP-C，提示cMyBP-C可能具有稳定SRX的作用。然而，来自cMyBP-C缺失小鼠的肌原纤维显示出约40%的SRX减少，不仅在现在无cMyBP-C的c区（49±9% SRX），而且在d区（22±5% SRX）。这些数据表明，cMyBP-C对SRX状态的影响并不局限于c区，而是沿着厚长丝延伸。有趣的是，N端截断的cMyBP-C肌原纤维的SRX含量和空间梯度与cMyBP-C null相似，这表明cMyBP-C的N端对于cMyBP-C增强整个粗丝SRX梯度的作用是必要的。考虑到SRX肌球蛋白沿厚丝呈梯度存在，且在c区最高，即使没有cMyBP-C或其n端，也必须在厚丝结构中存在固有的偏置以稳定SRX状态。
Striated muscle functional regulation occurs through the sequestration of myosin into the super-relaxed (SRX) state. Observing the turnover of single ATP molecules within cardiac sarcomeres defines the spatial arrangement of SRX myosin and their regulation by myosin-binding protein C. The myosin super-relaxed (SRX) state is central to striated muscle metabolic and functional regulation. In skeletal muscle, SRX myosin are predominantly colocalized with myosin-binding protein C (MyBP-C) in the sarcomere C-zone. To define how cardiac MyBP-C (cMyBP-C) and its specific domains contribute to stabilizing the SRX state in cardiac muscle, we took advantage of transgenic cMyBP-C null mice and those expressing cMyBP-C with a 271-residue N-terminal truncation. Utilizing super-resolution microscopy, we determined the lifetime and subsarcomeric location of individual fluorescent-ATP turnover events within isolated cardiac myofibrils. The proportion of SRX myosin demonstrated a gradient along the half-thick filament, highest in the P- and C-zones (72 ± 9% and 71 ± 6%, respectively) and lower in the D-zone (45 ± 10%), which lies farther from the sarcomere center and lacks cMyBP-C, suggesting a possible role for cMyBP-C in stabilizing the SRX. However, myofibrils from cMyBP-C null mice demonstrated an ∼40% SRX reduction, not only within the now cMyBP-C-free C-zone (49 ± 9% SRX), but also within the D-zone (22 ± 5% SRX). These data suggest that the influence of cMyBP-C on the SRX state is not limited to the C-zone but extends along the thick filament. Interestingly, myofibrils with N-terminal truncated cMyBP-C had an SRX content and spatial gradient similar to the cMyBP-C null, indicating that the N terminus of cMyBP-C is necessary for cMyBP-C’s role in enhancing the SRX gradient along the entire thick filament. Given that SRX myosin exist as a gradient along the thick filament that is highest in the C-zone, even in the absence of cMyBP-C or its N-terminus, an inherent bias must exist in the structure of the thick filament to stabilize the SRX state.
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DOI：
10.1085/jgp.202213087
发表时间：
2023-01-02
期刊：
The Journal of general physiology
影响因子：
--
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通讯作者：
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DOI：
10.1073/pnas.1809540115
发表时间：
2018-08-28
影响因子：
11.1
作者：
Anderson, Robert L.;Trivedi, Darshan V.;Spudich, James A.
通讯作者：
Spudich, James A.
影响因子：
4.8
作者：
Razumova, Maria V.;Shaffer, Justin F.;Harris, Samantha P.
通讯作者：
Harris, Samantha P.
影响因子：
16.8
作者：
Nag S;Trivedi DV;Sarkar SS;Adhikari AS;Sunitha MS;Sutton S;Ruppel KM;Spudich JA
通讯作者：
Spudich JA
影响因子：
3.7
作者：
McNamara, James W.;Li, Amy;dos Remedios, Cristobal G.
通讯作者：
dos Remedios, Cristobal G.