SOLUTION STRUCTURE OF THE B-CHAIN OF INSULIN AS DETERMINED BY H-1-NMRSPECTROSCOPY - COMPARISON WITH THE CRYSTAL-STRUCTURE OF THE INSULIN HEXAMER AND WITH THE SOLUTION STRUCTURE OF THE INSULIN MONOMER

The solution structure of the isolated B-chain of bovine insulin has b een determined by H-1 NMR spectroscopy combined with simulated anneali ng calculations. Complete sequence-specific assignments for the proton resonances are reported together with a set of 309 NOEs used in the s tructure calculations. Chemical-shift variations from random coil valu es provide support for the existence of helical regions in the polypep tide chain, as do a characteristic series of d(alpha beta)(i, i + 3) N OEs from residues B8 to B17. While there is some evidence for a limite d degree of conformational averaging over the helical region, in gener al the helix is relatively well defined and corresponds closely to the helical region seen in the X-ray crystal structure of the insulin hex amer. Other similarities with the crystal structure include turn-like conformations at the carboxy terminal end of the helix and extended st rands at both the amino and carboxy termini of the peptide. These simi larities between the crystal structure and the isolated B-chain sugges t that this peptide has intrinsic folding properties, which allow it t o adopt its characteristic structure in intact insulin without the nee d for extensive cooperative interactions with the A-chain. Despite the se general similarities, an important difference between the isolated B-chain and the intact protein occurs in the carboxy terminal region. This region appears significantly more mobile in the isolated B-chain. As a conformational change involving the carboxy terminus has been im plicated in receptor binding, the current study of the isolated B-chai n provides valuable information on the extent of this region's intrins ic mobility. (C) Munksgaard 1995.