Fig. 10. Sampling of χ1 and DIST2 order parameters in MD (∼600ns) and metadynamics simulations starting with apo PlmII (PDB ID:1LF4). The open flap conformation centres around DIST2 ∼ 2.0 nm. The gauche⁺ conformation was stabilised by H-bond interaction between Tyr and Trp whereas the trans conformation was stabilised by H-bond interaction between Tyr and catalytic Asp. The typical H-bond distance is 0.3–0.35 nm. z axis in the contour plot shows apparent free energy in kJ mol⁻¹.