Corrêa Fernando, Farah Chuck S, Salinas Roberto K
Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil.
Biopolymers. 2009 Jul;91(7):583-90. doi: 10.1002/bip.21185.
Tropomyosin (Tm) is a dimeric coiled-coil protein that polymerizes through head-to-tail interactions. These polymers bind along actin filaments and play an important role in the regulation of muscle contraction. Analysis of its primary structure shows that Tm is rich in acidic residues, which are clustered along the molecule and may form sites for divalent cation binding. In a previous study, we showed that the Mg(2+)-induced increase in stability of the C-terminal half of Tm is sensitive to mutations near the C-terminus. In the present report, we study the interaction between Mg(2+) and full-length Tm and smaller fragments corresponding to the last 65 and 26 Tm residues. Although the smaller Tm peptide (Tm(259-284(W269))) is flexible and to large extent unstructured, the larger Tm(220-284(W269)) fragment forms a coiled coil in solution whose stability increases significantly in the presence of Mg(2+). NMR analysis shows that Mg(2+) induces chemical shift perturbations in both Tm(220-284(W269)) and Tm(259-284(W269)) in the vicinity of His276, in which are located several negatively charged residues.
原肌球蛋白（Tm）是一种通过头尾相互作用聚合的二聚体卷曲螺旋蛋白。这些聚合物沿着肌动蛋白丝结合，并在肌肉收缩调节中发挥重要作用。对其一级结构的分析表明，Tm富含酸性残基，这些残基沿分子聚集，可能形成二价阳离子结合位点。在先前的一项研究中，我们表明镁离子（Mg(2+)）诱导的Tm C端半段稳定性增加对C端附近的突变敏感。在本报告中，我们研究了Mg(2+)与全长Tm以及对应于Tm最后65个和26个残基的较小片段之间的相互作用。尽管较小的Tm肽（Tm(259 - 284(W269))）具有柔性且在很大程度上无结构，但较大的Tm(220 - 284(W269))片段在溶液中形成卷曲螺旋，其稳定性在Mg(2+)存在下显著增加。核磁共振（NMR）分析表明，Mg(2+)在His276附近诱导Tm(220 - 284(W269))和Tm(259 - 284(W269))的化学位移扰动，His276附近有几个带负电荷的残基。
