Chain-length dependence of α-helix to β-sheet transition in polylysine:: Model of protein aggregation studied by temperature-tuned FTIR spectroscopy

The chain-length dependence of the alpha-helix to, beta-sheet transition in poly(L-lysine) is studied by temperature-tuned FTIR spectroscopy. This study shows that heterogeneous samples of poly(L-lysine), comprising polypeptide chains with various lengths, undergo the alpha-beta transition at an intermediate temperature compared to homogenous ingredients. This holds true as long as each individual fraction of the polypeptide is capable of adopting an, antiparallel beta-sheet structure. The tendency is that the longer chain is, the lower the alpha-beta transition temperature, is, which has been linked to the presence of distorted or solvated helices with turns or beta sheets in elongating chains of poly(L-lysine). As such helical structures are apparently conducive to the alpha-beta transition, this draws a comparison to the hypothesis of metastable protein conformational states being a common stage in amyloid-formation pathways. The antiparallel architecture of the P sheet is likely to reflect the pretransition interhelical interactions in poly(L-lysine). Namely, the chains are arranged in an antiparallel manner because of energetically favored antiparallel preassembly of dipolar a helices. (C) 2004 Wiley Peridicals, Inc.