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The alpha subunit of spectrin contains two EF-hands that bind Ca2+ with non-physiological affinity in vitro. Both undergo moderate conformational change, although it has been proposed that Ca2+ binding is sequential; EF2 (green and cyan cylinders on right) must bind Ca2+ before EF1 can bind. Interestingly, the movement of EF2 has been attributed to side-to-side packing with EF1, since EF2 itself lacks the hydrophobic core and aromatic residues key to the conformational change observed in EF1. |
| EF-hand (helix residues) | N-terminal coordinate
of second helix |
theta | phi | omega |
| apo-spectrin EF1 (14-21, 31-41) | (10.228, 0.179, -2.019) | 47.343 | 117.007 | 102 |
| apo-spectrin EF2 (57-64, 74-84) | (5.662, 7.792, -4.203) | 34.003 | 134.368 | 51 |
| Ca2+-spectrin EF1 (14-21, 31-41) | (6.803, -0.715, -5.806) | 47.217 | 69.474 | 92 |
| Ca2+-spectrin EF2 (57-64, 74-84) | (6.246, 2.524, -7.194) | 70.576 | 129.539 | 65 |
NB: values obtained using apo-CaM EF1 (as in refcam.pdb) as the reference EF-hand.