Figure 2.

The structure of α₂D, Ac-GEVEELEKKFKELWK-GPRRG-EIEELHKKFHELIKG-NH₂ (where the three residues in italics indicate the changes made to α₂C in the design of α₂D). (a) Topology diagram of α₂D showing the topology of the dimeric four-helix bundle that adopts the bisecting U motif. (b) Superposition of the backbone from the 15 lowest energy structures of α₂D calculated from NMR-derived data (PDB code 1QP6). (c) A cutaway view of a superposition of the 15 lowest energy NMR structures showing that Glu7 is not directly involved in stabilizing the native state of α₂D. Glu7 (shown in green and red) adopts several different conformations in solution, as opposed to the hydrophobic core residues (shown in gray).