Hydroxyproline bond angles

The tendencies of the amino acids to stabilize or destabilize a-helices are different in typical proteins than in polyamino acids. The occurrence of the common amino acids in helices is summarized in Table 6.1. Notably, proline (and hydroxyproline) act as helix breakers due to their unique structure, which fixes the value of the —N—C bond angle. Helices can be formed from either... 

Fig. 1. Interatomic bond lengths and bond angles for glycine (Marsh, 1958) L-proline (Mathieson and Welsh, 1952), and L-hydroxyproline (Donahue and True-blood, 1952).

Figure 11.3 The effect of imino acids on protein structure. The presence of the imino acids proline and hydroxyproline introduces a constraint into the angles of the peptide bond which results in a bend in the previously regular chain structure.

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