Mg2+ ions bind at the C‐terminal region of skeletal muscle α‐tropomyosin

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 Mg2+‐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 Mg2+ and full‐length Tm and smaller fragments corresponding to the last 65 and 26 Tm residues. Although the smaller Tm peptide (Tm259‐284(W269)) is flexible and to large extent unstructured, the larger Tm220‐284(W269) fragment forms a coiled coil in solution whose stability increases significantly in the presence of Mg2+. NMR analysis shows that Mg2+ induces chemical shift perturbations in both Tm220‐284(W269) and Tm259‐284(W269) in the vicinity of His276, in which are located several negatively charged residues. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 583–590, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com