Determinants of miniprotein stability: can anything replace a buried H-bonded Trp sidechain?

摘要

A novel 20-residue fold, designated the "Trp-cage' motif, has been shown to be 98+% folded in both water and 30 vol-% trifluoroethanol solution. Folding is cooperative and hydrophobically driven, resulting in the burial of the Trp sidechain and a stable H-bond from the Trp-εNH to a sequence remote backbone carbonyl. In the present study the effects of replacing the Trp with His, Phe and both isomers of β-naphthylalanine are examined. The results suggest that the hydrophobic cluster is a specific interaction of proline rings with the indole ring which can be partially mimicked by a naphthalene ring. The His and Phe mutants are completely unfolded in aqueous medium. The naphthylalanine mutants form a stable hydrophobic cluster in 30% trifluoroethanol, but are less stable in water than the native structure.