title: pH responsiveness of fibrous assemblies of repeat-sequence amphipathic α-helix polypeptides.
abstract: 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.
authors.affiliation: 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.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Takei
authors.forename: Kouhei
authors.initials: K
authors.lastname: Tsumoto
authors.forename: Atsuhito
authors.initials: A
authors.lastname: Okonogi
authors.forename: Akiko
authors.initials: A
authors.lastname: Kimura
authors.forename: Shuichi
authors.initials: S
authors.lastname: Kojima
authors.forename: Kazumori
authors.initials: K
authors.lastname: Yazaki
authors.forename: Tsunetomo
authors.initials: T
authors.lastname: Takei
authors.forename: Takuya
authors.initials: T
authors.lastname: Ueda
authors.forename: Kin-ichiro
authors.initials: K
authors.lastname: Miura
mesh_terms: D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D020449:Repetitive Sequences, Amino Acid
chemical_list: D010455:Peptides
keywords: aggregation; amphipathic α-helix; fibrous assembly; pH responsiveness; self-assembly