Direct observation of the multistep helix formation of poly-L-glutamic acids.
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.
Kimura
Tetsunari
T
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan.
Takahashi
Satoshi
S
Akiyama
Shuji
S
Uzawa
Takanori
T
Ishimori
Koichiro
K
Morishima
Isao
I
D002942:Circular Dichroism; D011099:Polyglutamic Acid / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared
D011099:Polyglutamic Acid