Insulin.
This page shows some interactive JSmol views of the (human) insulin hexamer structure.
Explore the structures for yourself:
The first figure shows an overview of the structure. Note the large number of associated water molecules (red spheres).
The assembly contains 12 protein chains - 6 A subunits and 6 B subunits.
In the next view, the water molecules have been removed; the disulfide bonds and histidine residues are included, and each subunit
is colored differently.
The disulfide bonds (yellow) link cysteine amino acids on A and B subunits - giving 6 AB pairs (hence the "hexameric" structure)
Note that most of the histidine residues are involved in coordination to zinc - and these interactions play a major part in
holding the hexamer together.
(What other interactions contribute?)
The final view emphasises the coordination sphere of the Zn2+ ion. The geometry at the metal ion is approximately tetrahedral and the
ligands are one chloride ion and three His residues, each from a different protein chain.
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Data are taken from:
Insulin, monoclinic form (homo sapiens). to be published
Turkenburg, M.G.W., Whittingham, J.L., Turkenburg, J.P., Dodson, G.G., Derewenda, U., Smith, G.D., Dodson, E.J., Derewenda, Z.S., Xiao,
B. (PDB code 1ZNJ).
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