© 2006 The Japanese Biochemical Society.
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The Effects of the Side Chains of Hydrophobic Aliphatic Amino Acid Residues in an Amphipathic Polypeptide on the Formation of
Helix and Its Association

Institute for Biomolecular Science, Gakusyuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588
To whom correspondence should be addressed at the present address: Research Institute, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016. Tel: +81-47-478-0526, Fax: +81-47-478-0527, E-mail: miurak{at}pf.it-chiba.ac.jp
The polypeptide
3, which was synthesized by us to produce an amphipathic helix structure, contains the regular three times repeated sequence (LETLAKA)3, and
3 forms a fibrous assembly. To clarify how the side chains of amino acid residues affect the formation of
helix, Leu residues, which are located in the hydrophobic surface of an amphipathic helix, were replaced by other hydrophobic aliphatic amino acid residues systematically, and the characters of the resulting polypeptides were studied. According to the circular dichroism (CD) spectra, the Ile-substituted polypeptides formed
helix like
3. However, their helix formation ability was weaker than that of
3 under some conditions. The Val-substituted polypeptides formed
helix only under restricted condition. The Ala-substituted polypeptides did not form
helix under any condition. Thus, it is clear that the order of the
helix formation ability is as follows: Leu
Ile > Val > Ala. The formation of
helix was confirmed by Fourier Transform Infrared (FTIR) spectra. Through electron microscopic observation, it was clarified that the formation of the
helix structure correlates with the formation of a fibrous assembly. The amphipathic
helix structure would be stabilized by the formation of the fibrous assembly.
* Present address: Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai-Cho, Nada-Ku, Kobe 657-8501.
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