Figure 3.

(a) Population distribution of the φ/ψ dihedrals in the four commonly observed backbone geometry regions as defined in the Ramachandran surface for amino acids 4 to 8/9. Arrows are used to highlight the formation of an α-helical fold in 9 and 11. (b) Probability distribution in the α_R region for amino acids 4, 5, 7 and the summed probability in the extended regions for amino acids 6, 7, 8. Backbone geometry regions are defined as α_R (−160° < φ< −20° and −120° < ψ< 50°), α_L (20° < φ< 160° and −50° <ψ< 120°), β (−180° < φ< −90° and 110° < ψ< 180°) and PPII (−90° < φ< −20° and 110° < ψ< 180°)