Alpha-helix to beta-sheet transition in long-chain poly-l-lysine: Formation of alpha-helical fibrils by poly-l-lysine.
The temperature-induced α-helix to β-sheet transition in long-chain poly-l-lysine (PLL), accompanied by the gauche-to-trans isomerization of CH2groups in the hydrocarbon side chains of Lys amino acid residues, and formation of β-sheet as well as α-helix fibrillar aggregates of PLL have been studied using Fourier-transform infrared (FT-IR) and vibrational circular dichroism (VCD) spectroscopy, and transmission electron microscopy (TEM). In a low-temperature alkaline water solution or in a methanol-rich water mixture, the secondary structure of PLL is represented by α-helical conformations with unordered and gauche-rich hydrocarbon side chains. Under these conditions, PLL molecules aggregate into α-helical fibrils. PLLs dominated by extended antiparallel β-sheet structures with highly ordered trans-rich hydrocarbon side chains are formed in a high-temperature range at alkaline pD and aggregate into fibrillar, protofibrillar, and spherical forms. Presented data support the idea that fibrillar aggregation is a varied phenomenon possible in repetitive structural elements with not only a β-sheet-rich conformation, but also an α-helical-rich conformation.
Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383 Wrocław, Poland. Electronic address: katarzyna.cieslik@chem.uni.wroc.pl.
Katarzyna
K
Cieślik-Boczula
D002942:Circular Dichroism; D006801:Humans; D046529:Microscopy, Electron, Transmission; D011107:Polylysine / Q000737:chemistry*; D000072756:Protein Conformation, alpha-Helical; D000072757:Protein Conformation, beta-Strand; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature
D011107:Polylysine
Infrared spectroscopy; Transmission electron microscopy; Vibrational circular dichroism; gauche-trans isomerization of protein CH(2) groups; α-Helix fibrils