Foldamer stability coupled to aggregation propensity of elongated trp-cage miniproteins

摘要

Here we present folding-associated aggregation propensity of three Trp-cage foldamers: E0 (20 aa), E5 (25 aa) and E10 (30 aa), models of different sizes but comparable molecular properties. Electronic circular dichroism (ECD), vibrational circular dichroism (VCD) and FT-IR spectroscopic measurements were used to monitor their concentration-dependent, heat-induced (5 °C → 65 °C) "α→β" fold transition. The ECD curves of E0 display an ensemble of highly dynamic structures. ECD of both E5 and E10 foldamers show the expected Trp-cage fold, dominated by their α-helical properties. No sign of β-structures was revealed by ECD at any conditions (5 °C < T < 65 °C, 5 < pH < 7, c ≈ 30 μM) for any of these miniproteins. However, at higher concentration (c ≈ 1-30 mM) both VCD and FT-IR spectral features of E5 as well as E10 resemble that of a β-strand (ca. 1615 cm~(-1)), accompanied with "free β-edges", or native β-sheets (ca. 1635 cm~(-1)). E5 at lower concentrations (c ≈ 1-3 mM), and E10 at higher concentration (c ≈ 30 mM) display the α→native-β→β-sheet folding transitions, monitored by the characteristic C=O vibrational normal mode frequency shift as follows: ca. 1650 cm~(-1) → ca. 1635 cm -1 → ca. 1615 cm~(-1), respectively. The latter folding path is irreversible. The shortest polypeptide E0 has an "unordered" fold, while E10 presents the most tightly packed Trp-cage 3D-structure. We have found that both high dynamicity and/or tight molecular core packing are different in nature, but common in efficacy in preventing the polypeptide backbone chain against self-aggregation. However, E5 is intermediate in size and stability, and thus among these three polypeptides it is the quickest to aggregate. The present molecular triad, E0, E5 and E10, serves as a good example of larger globular proteins for which aggregation and amyloid fiber-like nanoparticle formations are often associated with Alzheimer's, Creutzfeldt-Jakob, or prion diseases.