Dihedral angles of the observed R1 side chains in azurin T21R1. A polar plot is shown for each χ-angle. The angles measured in the R1-I/III conformation are plotted in A (coloured lines). The angles measured in the R1-II/IV conformation are plotted in B (coloured lines). The calculated angular distribution from the MTSSL rotamer library was digitized from  and is shown in each diagram (grey lines).