Guanidinium derivatives bind preferentially and trigger long-distance conformational changes in an engineered T4 lysozyme

Molecular dynamics simulations of an engineered T4 lysozyme exclude helix to sheet transition, and provide insights into long distance, intra-protein switchable motion

An engineered variant of T4 lysozyme serves as a model for studying induced remote conformational changes in a full protein context. The design involves a duplicated surface helix, flanked by two loops, that switches between two different conformations spanning about 20 Å. Molecular dynamics simulations of the engineered protein, up to 1 μs, rule out α-helix to β-sheet transitions within the duplicated helix as suggested by others. These simulations highlight how the use of different force fields can lead to radical differences in the structure of the protein. In addition, Markov state modeling and transition path theory were employed to map a 6.6 μs simulation for possible early intermediate states and to provide insights into the onset of the switching motion. The putative intermediates involve the folding of one helical turn in the C-terminal loop through energy driven, sequential rearrangement of nearby salt bridges around the key residue Arg63. These results provide a first step towards understanding the energetics and dynamics of a rather complicated intra-protein motion.

Duplication of a Single Strand in a β-Sheet Can Produce a New Switching Function in a Photosensory Protein

Duplication of a single β-strand that forms part of a β-sheet in photoactive yellow protein (PYP) was found to produce two approximately isoenergetic protein conformations, in which either the first or the second copy of the duplicated β-strand participates in the β-sheet. Whereas one conformation (big-loop) is more stable at equilibrium in the dark, the other conformation (long-tail) is populated after recovery from blue light irradiation. By appending a recognition motif (E-helix) to the C-terminus of the protein, we show that β-strand duplication, and the resulting possibility of β-strand slippage, can lead to a new switchable protein-protein interaction. We suggest that β-strand duplication may be a general means of introducing two-state switching activity into protein structures.