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. Author manuscript; available in PMC: 2014 Oct 27.
Published in final edited form as: J Am Chem Soc. 2013 Mar 11;135(11):4333–4363. doi: 10.1021/ja3109664

Figure 3.

Figure 3

Effects of proline ring pucker on main chain φ, ψ, and ω torsion angles. (a) 4-Substituted proline residues can bias proline ring pucker by stereoelectronic effects or by steric effects. (b) An n→π* interaction between the carbonyl lone pair (n) of residue i and the π* orbital of the carbonyl on the subsequent residue (i+1) provides local organization of the protein main chain, including stabilization of the trans amide bond and the αR and PPII conformations. This interaction is preferential with the Cγ-exo ring pucker of proline and is only possible with a trans amide bond.