C-terminal troponin-I residues trap tropomyosin in the muscle thin filament blocked-state.
C-terminal troponin-I residues trap tropomyosin in the muscle thin filament blocked-state.
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DOI：
10.1016/j.bbrc.2021.03.010
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发表时间：
2021-04-30
影响因子：
3.1
通讯作者：
Rynkiewicz MJ
中科院分区：
文献类型：
--
作者：
Lehman W;Pavadai E;Rynkiewicz MJ
原肌凝蛋白和肌钙蛋白通过参与大分子尺度的立体机制来控制肌凝蛋白-过桥-肌动蛋白的相互作用，从而调节肌肉收缩。在低ca2 +时，30%的肌钙蛋白亚单位- i （TnI）的c端被认为将原肌凝蛋白困在细丝上的位置，从而在空间上干扰肌凝蛋白结合，从而导致肌肉松弛。相反，在高ca2 +的情况下，当c端结构域与F-actin-tropomyosin分离后，其成分开关肽结构域与肌钙蛋白- c （TnC）的n叶结合时，抑制被释放。最近，由Namba小组进行的范式转换，低温电镜重建揭示了在低和高ca2 +浓度下沿心肌细丝的TnI密度。重建模型显示了TnI开关肽和TnC的高ca2 +疏水相互作用。然而，在低ca2 +条件下，在已发表的模型中，TnI和原肌球蛋白的稀疏相互作用，特别是非极性开关肽残基和带电荷的原肌球蛋白氨基酸的并立似乎难以与预期的立体阻断构象相协调。这种异常可能是由于原肌球蛋白与冷冻电镜体积的不准确拟合。在目前的研究中，低ca2 +冷冻电镜体积与更准确的原肌球蛋白模型和心脏TnI的代表相匹配。我们的研究结果表明，在低ca2 +下，TnI开关肽和相邻H4螺旋上的疏水残基簇（Ala149, Ala151, Met 154, Leu159, Gly160, Ala161, Ala163, Leu167, Leu169, Ala171, Leu173）吸引原肌球蛋白表面残基（Ile143, Ile146, Ala151, Ile154），可能会吸引整个原肌球蛋白电缆到肌动蛋白上的肌球蛋白阻断位置。模型证实邻近的TnI“抑制结构域”残基（Arg145, Arg148）与肌动蛋白残基Asp25的细丝结合，正如之前所建议的那样。ClusPro将TnI残基137-184与肌动蛋白原肌球蛋白（actin-tropomyosin）对接，包括TnI抑制结构域、开关肽和Helix H4，验证了模型结构。我们的tni -原肌球蛋白关联的残基-残基接触图谱有助于对致病突变进行实验验证和功能定位。
Tropomyosin and troponin regulate muscle contraction by participating in a macromolecular scale steric-mechanism to control myosin-crossbridge – actin interactions and consequently contraction. At low-Ca2+, the C-terminal 30% of troponin subunit-I (TnI) is proposed to trap tropomyosin in a position on thin filaments that sterically interferes with myosin-binding, thus causing muscle relaxation. In contrast, at high-Ca2+, inhibition is released after the C-terminal domains dissociate from F-actin-tropomyosin as its component switch-peptide domain binds to the N-lobe of troponin-C (TnC). Recent, paradigm-shifting, cryo-EM reconstructions by the Namba group have revealed density attributed to TnI along cardiac muscle thin filaments at both low- and high-Ca2+ concentration. Modeling the reconstructions showed expected high-Ca2+ hydrophobic interactions of the TnI switch-peptide and TnC. However, under low-Ca2+ conditions, sparse interactions of TnI and tropomyosin, and in particular juxtaposition of non-polar switch-peptide residues and charged tropomyosin amino acids in the published model seem difficult to reconcile with an expected steric-blocking conformation. This anomaly is likely due to inaccurate fitting of tropomyosin into the cryo-EM volume. In the current study, the low-Ca2+ cryo-EM volume was fitted with a more accurate tropomyosin model and representation of cardiac TnI. Our results show that at low-Ca2+ a cluster of hydrophobic residues at the TnI switch-peptide and adjacent H4 helix (Ala149, Ala151, Met 154, Leu159, Gly160, Ala161, Ala163, Leu167, Leu169, Ala171, Leu173) draw-in tropomyosin surface residues (Ile143, Ile146, Ala151, Ile154), presumably attracting the entire tropomyosin cable to its myosin-blocking position on actin. The modeling confirms that neighboring TnI “inhibitory domain” residues (Arg145, Arg148) bind to thin filaments at actin residue Asp25, as previously suggested. ClusPro docking of TnI residues 137–184 to actin-tropomyosin, including the TnI inhibitory-domain, switch-peptide and Helix H4, verified the modeled configuration. Our residue-to-residue contact-mapping of the TnI-tropomyosin association lends itself to experimental validation and functional localization of disease-bearing mutations.
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影响因子：
4
作者：
Liu X;Zhang L;Pacciulli D;Zhao J;Nan C;Shen W;Quan J;Tian J;Huang X
通讯作者：
Huang X
影响因子：
14.8
作者：
Kozakov D;Hall DR;Xia B;Porter KA;Padhorny D;Yueh C;Beglov D;Vajda S
通讯作者：
Vajda S
影响因子：
15
作者：
Metskas LA;Rhoades E
通讯作者：
Rhoades E
影响因子：
2.9
作者：
Kozakov, Dima;Hall, David R.;Beglov, Dmitri;Brenke, Ryan;Comeau, Stephen R.;Shen, Yang;Li, Keyong;Zheng, Jiefu;Vakili, Pirooz;Paschalidis, Ioannis Ch.;Vajda, Sandor
通讯作者：
Vajda, Sandor
影响因子：
3
作者：
Poole, Katrina J. V.;Lorenz, Michael;Holmes, Kenneth C.
通讯作者：
Holmes, Kenneth C.