A ribbon representation of the N-domain of TnC in the apo state (1SPY(40)) is shown on the left; in the Ca2+ bound state (1AP4 (40) is shown in the middle; and in the Ca2+ saturated Tn state (1J1E (23), TnI and TnT have been omitted for clarity) is shown on the right. The helices are labeled (N, A, B, C, and D); while hydrophobic residues that were mutated (F20, V44, M45, L48 and M81) are shown in a ball-and-stick format and labeled. The figure was generated using Rasmol (24).