Figure 2.4.

Conformation of Gly^B8 in a T-state-specific α-turn. (A) Sequence of B chain (top) and A chain (bottom); arrow indicates invariant Gly^B8 (red). Shown above B chain in magenta are the three substitutions in the monomeric DKP template. (B) Cylinder models of TR dimer based on crystal structure of zinc insulin hexamers (PDB ID: 1TRZ). The T state is at left and R state at right. B-chain α-helices are shown in green; the α-carbons of Gly^B8 are shown as red circles. Three families of hexamers have been characterized, designated T₆, ${\mathrm{T}}_3{\mathrm{R}}_3^{\mathrm{f}}$, and R₆. The R-state conformation has only been observed within hexamers. (C) Structure of insulin T state (stereo pair) showing positions of selected side chains (labeled at left) relative to Gly^B8 C_α (red) and disulfide bridges (gold; labeled at right). The B chain is shown in green, and A chain in black. (D) Structure of T-state-specific B7–B10 β-turn (stereo pair). Main chain of Gly^B8 is shown in red; its pro-l and pro-d H_α atoms are highlighted in blue and magenta, respectively. This figure is reprinted from Hua et al. (2006b).