Crystal structure of insulin (PDB ID: 9INS)  with 90° rotation.
Dark colored (blue) element corresponds to chain-A and light colored (green) to chain-B of insulin in the central structures. The three disulfide bond of insulin have been shown by solid arrows. The dotted arrows indicate the N- and C-terminal segments of chain-B. The dotted spheres on the left hand side of the figure show the central hydrophobic core of insulin. The surface potential of insulin molecule (blue - positive; red – negative) obtained after processing by PDB2PQR  and APBS  has been shown on the right hand side of the figure. The proposed model of insulin fibrillation is depicted at the bottom of the figure (see text for details).