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Intrahelical Interactions in an α-Helical Coiled Coil Determine the Structural Stability of Tropomyosin

Ken-Ichi Sano1,2, Tsubasa Yuki2, Yuta Nomata2

  • 1Department of Applied Chemistry, Faculty of Fundamental Engineering, Nippon Institute of Technology, Miyashiro, Saitama 345-8501, Japan.

Biochemistry
|May 30, 2020
PubMed

Insights

Structural stability of tropomyosin (Tpm) and its variants is governed by multivalent ion binding to single alpha-helices, not interhelical interactions. This finding redefines understanding of coiled-coil protein structure.

Area of Science:

  • Biochemistry
  • Structural Biology
  • Protein Science

Background:

  • Tropomyosin (Tpm) is a key coiled-coil protein essential for muscle function.
  • Previous studies indicated reduced structural stability of Tpm variants in the presence of phosphate ions.
  • A prevailing hypothesis attributed coiled-coil stability to interhelical interactions.

Purpose of the Study:

  • To investigate the hypothesis that multivalent ion binding to charged residues dictates Tpm structural stability.
  • To elucidate the role of specific ion interactions in stabilizing single alpha-helices within coiled-coil structures.
  • To compare the stability mechanisms of human skeletal muscle alpha-Tpm (α-Tpm 140) and a conserved coiled-coil protein carrier (CCPC) 140 variant.

Main Methods:

  • Comparative analysis of α-Tpm 140 and CCPC 140 structural stability.
  • Assessment of structural stability upon addition of divalent cations and anions.
  • Investigation of heteromeric coiled-coil molecule stability.

Main Results:

  • Structural stability of both α-Tpm 140 and CCPC 140 significantly increased with the addition of specific divalent ions.
  • Divalent cations enhanced α-Tpm 140 stability, while divalent anions stabilized CCPC 140.
  • The stability of heteromeric α-Tpm 140/CCPC 140 molecules was determined by the less stable individual alpha-helical chain.

Conclusions:

  • Coiled-coil protein structural stability is primarily governed by the binding of multivalent ions to single alpha-helices.
  • Interhelical interactions are not the sole determinants of coiled-coil stability.
  • Findings challenge classical hypotheses and offer novel insights into coiled-coil protein structure and dynamics.

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