title: Direct observation of the multistep helix formation of poly-L-glutamic acids.
abstract: The helix formation dynamics of poly-L-glutamic acids (PGAs) were observed by the microsecond-resolved Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopies. The helix formation of 34-residue PGA from random coil at pH (or pD for FTIR) 8.0 was initiated by a pH jump to 4.9 using the rapid solution mixer whose mixing dead time is 50 micros. The amide I' line in the time-resolved FTIR spectra exhibited the fast (<100 micros) increase of the total helical content. The time-resolved CD spectra of the same process also showed the fast (<150 micros) formation of short helical segments (5 +/- 1 residues), which was followed by the slower (<1 ms) elongation of the short helices to longer helices (>10 residues). Similar dynamics were observed for the same pH jump of approximately 190-residue PGA, although there were additional steps that made the helix formation of approximately 190-residue PGA more complex. The observed multistep helix formation is likely caused by the strong hydrogen-bonding interactions between the protonated side chains of PGAs.
authors.affiliation: Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Tetsunari
authors.initials: T
authors.lastname: Kimura
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takahashi
authors.forename: Shuji
authors.initials: S
authors.lastname: Akiyama
authors.forename: Takanori
authors.initials: T
authors.lastname: Uzawa
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ishimori
authors.forename: Isao
authors.initials: I
authors.lastname: Morishima
mesh_terms: D002942:Circular Dichroism; D011099:Polyglutamic Acid / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D011099:Polyglutamic Acid