Table 2.
Inter-helical angles of various EF hands.
| Calcium Binding Protein | Interhelical angles(°)a | Accession Code (PDB) | |
|---|---|---|---|
| A-B | C-D | ||
| cNTnC·apo (NMR) | 140±3 | 128±4 | 1SPY |
| cNTnC·Ca2+ (NMR) | 132±3 | 113±4 | 1AP4 |
| cNTnC·Ca2+·cTnI147-163 (NMR) | 102±5 | 96±5 | 1MXL |
| cTnC·3Ca2+·cTnI31-210·cTnT183-288 (X-RAY) | 103 | 96 | 1J1E |
| cNTnC·Ca2+·bepridil·cTnI147-163 (NMR) | 121±4 | 91±4 | 1LXF |
| cTnC·3Ca2+·bepridil (X-RAY) | 92 | 90 | 1DTL |
| cNTnC·Ca2+·W7 (NMR) | 114±3 | 92±2 | 2KFX |
| cNTnC·Ca2+·W7·cTnI147-163 (NMR) | 113±5 | 66±4 | 2KRD |
| CaM(N-domain) ·Ca2+·W7 (NMR) | 102±4 | 75±5 | 1MUX |
| CaM(C-domain) ·Ca2+·W7 (NMR) | 105±4 | 85±4 | 1MUX |
The 180° interhelical angle corresponding to a completely closed EF hand domain (antiparallel helices), whereas 0° angle defines a completely open conformation (parallel helices). The extent of openness is characterized by the A/B and C/D interhelical angles. cNTnC in 2KRD is open as compared to the closed 1SPY or 1AP4. The A/B helical pair is more closed than 1MXL, while the C/D pair is more open. As compared to 2KFX, the A/B pair is similar but the C/D pair is more open. Both the A/B and C/D pairs of 2KRD are more open than cNTnC in 1LXF. While the C/D helical pair in this complex is more open than that in all the open cNTnC structures, it is similar to the corresponding helical pair in CaM(N-domain)•2Ca2+•W7 and CaM(C-domain)•2Ca2+•W7.
The axis for an α-helix is defined by two points, taken as the average coordinates of the first and last 11 backbone atoms of the α-helix. Inter-helical angels were calculated using the program interhelix (K. Yap, University of Toronto).