Structural relationships in the two-zinc insulin hexamer

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Abstract
The refinement of the crystal structure of 2-Zn pig insulin using 1.5-.ANG. (1 .ANG. = 0.1 nm) resolution data by Fourier and fast Fourier least-squares methods allows one to make detailed comparisons between the 2 independent molecules present in the 2-Zn insulin dimer and to describe their interactions in the monomer, dimer and hexamer. The main chain structures for the 2 molecules agree well except at the N terminus of the A chain and the C terminus of the B chain. The residues along the line of the local 2-fold axes, apart from the B25 side chain, conform extremely closely to the 2-fold symmetry, although the discrepancies are much more apparent away from this axis. The ability of the insulin molecule to adopt different conformations may be an important factor in the expression of its biological activity.
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