Disulphide BridgesDisulphide bridges are identified for two cysteine residues whose sulphur atoms are less than 3Å apart. Richardson (1981) identified several categories of disulphide bridges based on their internal chi angles, in particular the chi2, chi3 and chi2' angles. We have loosely classified disulphides based on the signs of these angles into 5 categories. These are shown below.
Disulphide type Chi2 Chi3 Chi2' left handed spiral (LHS) - - - right handed hook (RHH) + + - right handed spiral (RHS) + + + short right handed hook (SRH) - + -
Note that the chi2 and chi2' values can be interchanged, as they merely reflect which of the two cysteines involved in the bridge is mentioned first. If the other cysteine were mentioned first the chi and chi' values would be interchanged.
Richardson found that the majority of disulphides could be classed as left handed spirals or right handed hooks.
The data displayed for each disulphide bridge is as follows: The table shows the residue numbers of the two cysteines involved in the disulphide bridge and the type of disulphide. The type of bridge is abbreviated (RHH: right hand hook; SRH: short right hand hook; LHS: left handed spiral; RHS: right handed spiral). Chi1, chi2, chi3, chi2' and chi1' values and the distance between the Calpha atoms of the residues involved are also recorded.