Secondary structure simulations of twin-arginine signal peptides in different environments

The twin-arginine translocation (Tat) system transports folded proteins across bacterial plasma membranes and the chloroplast thylakoid membrane. A twin-arginine motif in the signal peptide sequence plays a key role in the signal process. In this article we report the results of molecular dynamics simulations on a typical Escherichia coli RR-signal peptide and two mutant variants in both aqueous and trifluoroethanol (TFE) solutions. It has been found that the peptide switches between two distinct states: random coil in water and some helical content in TFE. Our simulations demonstrate that the wild-type peptide is considerably more flexible than either of the mutants in both the solvents investigated. The twin-arginine motif was found to provide a nucleation point for the formation of an -helix in water, but also appears to destabilise -helices in other regions of the peptide when dissolved in TFE