The pressure tolerance of different poly-l-lysine conformers in aqueous solution: Infrared spectroscopy and two-dimensional correlation analysis

Poly-l-lysine can form either of three different conformers as α-helix, anti-parallel β-sheet and random coil stably under appropriate conditions. In buffer solution poly-l-lysine exists in a random coil at about pH 4, an α-helix above pH 12, and transforms from α-helix to β-sheet when the sample is heated to 46 °C for 30 min. The effects of elevated hydrostatic pressure on three different initial conformers of poly-l-lysine are investigated with Fourier transform infrared spectroscopy and two-dimensional correlation analysis. Changes observed in the amide I′ band indicate that the α-helix conformer undergo hydration enhancement at low pressure (<400 MPa), then gradually transition into an α′-helix. Two initial conformers, the β-sheet and random coiled polypeptide, undergo conformational changes to an α-helix at low pressure and to an α′-helix at high pressure. Moreover, the conversion occurred at a lower pressure for the β-sheet (∼250 MPa) than for the α-helix (∼300 MPa) and the random coil (∼850 MPa).