Energy landscape of the ribosomal decoding center

The ribosome decodes the genetic information that resides in nucleic acids. A key component of the decoding mechanism is a conformational switch in the decoding center of the small ribosomal subunit discovered in high-resolution X-ray crystallography studies. It is known that small subunit nucleotides A1492 and A1493 flip out of helix 44 upon transfer RNA (tRNA) binding; however, the operation principles of this switch remain unknown. Replica molecular dynamics simulations reveal a low free energy barrier between flipped-out and flipped-in states, consistent with a switch that can be controlled by shifting the equilibrium between states. The barrier determined by the simulations is sufficiently small for the binding of ligands, such as tRNAs or aminoglycoside antibiotics, to shift the equilibrium.