Effects of Chain Length of an Amphipathic Polypeptide Carrying the Repeated Amino Acid Sequence (LETLAKA)n on 伪-Helix and Fibrous Assembly Formation

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• 作者：Toshiaki Takei ; Kazuya Hasegawa ; Katsumi Imada ; Keiichi Namba ; Kouhei Tsumoto ; Yukino Kuriki ; Masakuni Yoshino ; Kazumori Yazaki ; Shuichi Kojima ; Tsunetomo Takei ; Takuya Ueda ; Kin-ichiro Miura
• 刊名：Biochemistry
• 出版年：2013
• 出版时间：April 23, 2013
• 年：2013
• 卷：52
• 期：16
• 页码：2810-2820
• 全文大小：589K
• 年卷期：v.52,no.16(April 23, 2013)
• ISSN：1520-4995

文摘

Polypeptide 伪3 (21 residues), with three repeats of a seven-amino-acid sequence (LETLAKA)₃, forms an amphipathic 伪-helix and a long fibrous assembly. Here, we investigated the ability of 伪3-series polypeptides (with 14鈥?2 residues) of various chain lengths to form 伪-helices and fibrous assemblies. Polypeptide 伪2 (14 residues), with two same-sequence repeats, did not form an 伪-helix, but polypeptide 伪2L (15 residues; 伪2 with one additional leucine residue on its carboxyl terminal) did form an 伪-helix and fibrous assembly. Fibrous assembly formation was associated with polypeptides at least as long as polypeptide 伪2L and with five leucine residues, indicating that the C-terminal leucine has a critical element for stabilization of 伪-helix and fibril formation. In contrast, polypeptides 伪5 (35 residues) and 伪6 (42 residues) aggregated easily, although they formed 伪-helices. A 15鈥?5-residue chain was required for fibrous assembly formation. Electron microscopy and X-ray fiber diffraction showed that the thinnest fibrous assemblies of polypeptides were about 20 脜 and had periodicities coincident with the length of the 伪-helix in a longitudinal direction. These results indicated that the 伪-helix structures were orientated along the fibrous axis and assembled into a bundle. Furthermore, the width and length of fibrous assemblies changed with changes in the pH value, resulting in variations in the charged states of the residues. Our results suggest that the formation of fibrous assemblies of amphipathic 伪-helices is due to the assembly of bundles via the hydrophobic faces of the helices and extension with hydrophobic noncovalent bonds containing a leucine.