Takei Toshiaki, Tsumoto Kouhei, Okonogi Atsuhito, Kimura Akiko, Kojima Shuichi, Yazaki Kazumori, Takei Tsunetomo, Ueda Takuya, Miura Kin-ichiro
Department of Medical Genome Sciences, Graduate School of Frontier, The university of Tokyo, Kashiwanoha, Kashiwa, Chiba, Japan; Institute for Biomolecular Science, Gakushuin University, Toshima-ku, Tokyo, Japan.
Protein Sci. 2015 May;24(5):883-94. doi: 10.1002/pro.2665. Epub 2015 Apr 2.
We reported previously that our designed polypeptide α3 (21 residues), which has three repeats of a seven-amino-acid sequence (LETLAKA)3, forms not only an amphipathic α-helix structure but also long fibrous assemblies in aqueous solution. To address the relationship between the electrical states of the polypeptide and its α-helix and fibrous assembly formation, we characterized mutated polypeptides in which charged amino acid residues of α3 were replaced with Ser. We prepared the following polypeptides: 2Sα3 (LSTLAKA)3, in which all Glu residues were replaced with Ser residues; 6Sα3 (LETLASA)3, in which all Lys residues were replaced with Ser; and 2S6Sα3 (LSTLASA)3; in which all Glu and Lys residues were replaced with Ser. In 0.1M KCl, 2Sα3 formed an α-helix under basic conditions and 6Sα3 formed an α-helix under acid conditions. In 1M KCl, they both formed α-helices under a wide pH range. In addition, 2Sα3 and 6Sα3 formed fibrous assemblies under the same buffer conditions in which they formed α-helices. α-Helix and fibrous assembly formation by these polypeptides was reversible in a pH-dependent manner. In contrast, 2S6Sα3 formed an α-helix under basic conditions in 1M KCl. Taken together, these findings reveal that the charge states of the charged amino acid residues and the charge state of the Leu residue located at the terminus play an important role in α-helix formation.
我们之前报道过，我们设计的多肽α3（21个残基），具有七氨基酸序列（LETLAKA）3的三个重复序列，在水溶液中不仅形成两亲性α-螺旋结构，还形成长纤维聚集体。为了研究多肽的电状态与其α-螺旋和纤维聚集体形成之间的关系，我们对α3中带电氨基酸残基被丝氨酸取代的突变多肽进行了表征。我们制备了以下多肽：2Sα3（LSTLAKA）3，其中所有Glu残基被Ser残基取代；6Sα3（LETLASA）3，其中所有Lys残基被Ser取代；以及2S6Sα3（LSTLASA）3，其中所有Glu和Lys残基被Ser取代。在0.1M KCl中，2Sα3在碱性条件下形成α-螺旋，6Sα3在酸性条件下形成α-螺旋。在1M KCl中，它们在较宽的pH范围内均形成α-螺旋。此外，2Sα3和6Sα3在形成α-螺旋的相同缓冲条件下形成纤维聚集体。这些多肽形成α-螺旋和纤维聚集体的过程在pH依赖的方式下是可逆的。相比之下，2S6Sα3在1M KCl的碱性条件下形成α-螺旋。综上所述，这些发现表明带电氨基酸残基的电荷状态以及位于末端的Leu残基的电荷状态在α-螺旋形成中起重要作用。
