Thermal stability of the synthetic peptides with the sequence of fish fast skeletal muscle tropomyosin

Tropomyosins from fish skeletal muscle show high amino acid sequence homology, although their thermal stability is clearly different among species. In order to determine the regions that are responsible for the stability of this protein, five synthetic peptides of 30mer were synthesized by Fmoc method, based on the sequence of walleye pollack Theragra chalcogramma fast skeletal muscle tropomyosin, namely, N terminal Met¹-Lys³⁰, the variable region Asp⁸⁴-Leu¹¹³, the middle region Val¹²⁸-Ala¹⁵⁷, the region containing the conservative Cys (Leu¹⁷⁶-Lys²⁰⁵), and C terminal Asp²⁵⁵-Ile²⁸⁴. The thermal stability of these peptides was measured by circular dichroism and differential scanning calorimetry. The helical contents of these peptides were decreased in a temperature-dependent manner, although they showed no clear melting temperature, suggesting that the enthalpy necessary for the complete denaturation of these peptides was low. Peptides Asp²⁵⁵-Ile²⁸⁴ and Asp⁸⁴-Leu¹¹³ showed the highest and second highest α-helical contents, respectively, and the other peptides gave rise to lower α-helical contents.