Well-tempered metadynamics 4,29 calculations were carried out with GROMACS 2016.3 1 in combination with plumed 2.3.1. A bias factor of (T + ∆T )/T = 11 with a time constant of τ = 10 ps, a time step of 0.002 ps, and a tempearture T = 298 K were used for 100 ns simulations started from apo structures previously equilibrated as described above. Every τ pace = 2 ps Gaussian biases of 5 degree width and an initial height of k b ∆T τ pace /τ = 2k b T ≈ 4.955 kJ/mol, where k b is the Boltzmann constant, were deposited onto a periodic grid consisting of 360 points equally distributed along the χ1 dihedral. Resulting free energy surfaces and uncertainties are reported as averages and standard deviations across 5 repeats.