Insulin monomer, crystal structure

Fig. 3. Refolding model of insulin protofilaments, from Jimenez et al. (2002). (A) Ribbon diagram of the crystal structure of porcine insulin (PDB ID code 3INS), generated with Pymol (DeLano, 2002). The two chains are shown as dark and light gray with N- and C-termini indicated. The dotted lines represent the three disulfide bonds 1 is the intrachain and 2 and 3 are the interchain bonds. (B) Cartoon representation of the structure of monomeric insulin in the fibril, as proposed by Jimenez et al. (2002). The thick, arrowed lines represent /1-strands, and thinner lines show the remaining sequence. The disulfide bonds are as represented in panel A, and N- and C-termini are indicated. (Components of this panel are not to scale.) (C) Cartoon representation of an insulin protofilament, showing a monomer inside. The monomers are proposed to stack with a slight twist to form two continuous /(-sheets. (Components of this panel, including the protofilament twist, are not to scale.) In the fibril cross sections presented byjimenez et al. (2002), two, four, or six protofilaments are proposed to associate to form the amyloid-like fibrils.

Figure 2. The crystal structure of the insulin monomer viewed perpendicular to the threefold axis. The backbone of the A chain is represented by a double line and that of the B chain by a heavy line. From Blundell et al (1972).

Figure 2.11 In situ STM of human insulin on single-crystal Au electrode surfaces [1 70], At left is a structural representation of the expected dominating insulin dimer form (PDB 1 B9E). The A- and B-chains and the three disulfide groups in each monomer (blue, red,...

X-ray, circular dichroism, and centrifuge studies have demonstrated that most mammalian and fish insulins form zinc insulin hexamers similar to those of porcine insulin (Blundell et al, 1972 Blundell and Wood, 1975), with the exception of hagfish insulin, which produces only dimers (Cutfield et al, 1974 Peterson et al, 1974), and guinea pig (Zimmerman et al, 1972), casiragua (Horuk et al, 1979), and porcupine (Horuk et al, 1980) insulins, which exist only as monomers. A complete structural analysis of hagfish insulin dimers shows that, unlike porcine insulin, the two molecules of the dimer in the crystals are exactly equivalent and resemble molecule II of the asymmetric dimer of porcine insulin. This is similar to the structure of porcine insulin in solution as indicated by circular dichroism studies (Wood et al, 1975 Strickland and Mercola, 1976). 

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