Biphasic effects of alcohols on the phase transition of poly(L-lysine) between alpha-helix and beta-sheet conformations.
Poly(L-lysine) exists as a random-coil at neutral pH, an alpha-helix at alkaline pH, and a beta-sheet when the alpha-helix poly(L-lysine) is heated. The present Fourier-transform infrared (FTIR) study showed that short-chain alcohols (methanol, ethanol, and 2-propanol) partially transformed alpha-helix poly(L-lysine) to beta-sheet when their concentrations were low. At higher concentrations, however, these alcohols reversed the reaction, and the alcohol-induced beta-sheet was transformed back to alpha-helix structure. The reversal occurred at 1.40 M methanol, 0.96 M ethanol, and 0.55 M 2-propanol. The alcohol effects on the secondary structure were further investigated by circular dichroism (CD) on the thermally induced beta-sheet poly(L-lysine). Methanol, ethanol, and 1-propanol, but not 1-butanol, shifted the negative mean-residue ellipticity at 217 nm of the beta-sheet poly(L-lysine) to the positive side at low concentrations of the alcohols and to the negative side at high concentrations. With 1-butanol, only the positive-side shift was observed. The positive-side shift at low concentrations of alcohols indicates enhancement of the hydrophobic interactions among the side chains of the polypeptide in the beta-sheet conformation. The negative-side shift indicates a partial transformation to alpha-helix. The shift from the positive to negative side occurred at 7.1 M methanol, 4.6 M ethanol, and 3.1 M 1-propanol. The alcohol concentrations for the beta-to-alpha transition were higher in the CD study than in the IR study.(ABSTRACT TRUNCATED AT 250 WORDS)
Shibata
A
A
Faculty of Pharmaceutical Sciences, Tokushima University, Japan.
Yamamoto
M
M
Yamashita
T
T
Chiou
J S
JS
Kamaya
H
H
Ueda
I
I
D000433:1-Propanol / Q000494:pharmacology*; D002942:Circular Dichroism; D000431:Ethanol / Q000494:pharmacology*; D005583:Fourier Analysis; D006860:Hydrogen Bonding; D000432:Methanol / Q000494:pharmacology*; D011107:Polylysine / Q000737:chemistry*; D011487:Protein Conformation / Q000187:drug effects; D013055:Spectrophotometry, Infrared
D011107:Polylysine; D000431:Ethanol; D000433:1-Propanol; D000432:Methanol