Figure 2.

Geometric parameters for 2 cysteine residues forming a disulfide bond, focusing on the C^α–C^β bonds of cysteine residues i and j. It is convenient to define a pseudo-bond between the β-carbons (upper). The resulting pseudo-bond length $r_{ij}^{\beta }$, pseudo-dihedral angle ${\chi }_{ij}^{\beta }$, and pseudo-bond angles θ_ij and θ_ji are used to determine whether the residues have a relative geometry suitable for disulfide formation (Balaji et al., 1989).