Figure 4.

Illustration of the prediction of the χ₁ probability distribution using Val in the α-helix backbone conformation. We sampled χ₁ from 0° to 360° and θ₁ and θ₂ from 0° to 120° every 5°. Each data point is colored from white (no clashes) to dark red (highest number of clashes). (A, top panel) The layer at χ₁ = 40° with no white data points corresponds to probability P_calc = 0 as indicated in the bottom panel. (B, top panel) The layer at χ₁ = 175° with approximately one-eighth of all possible θ₁ and θ₂ allowed combinations corresponds to point B in the lower panel. The same calculations are performed for all sampled values of χ₁ (and shown as the blue points in the lower panel). The probability P_calc is normalized so that the area below the curve is 1. (The set of atom sizes used to calculate P_calc is indicated by the star symbols in Fig. 3.)