1H nuclear-magnetic-resonance studies of the molecular conformation of monomeric glucagon in aqueous solution.

Dilute aqueous solutions of glucagon were investigated by high-resolution 1H nuclear magnetic resonance at 360 MHZ. Monomeric glucagon was found to adopt predominantly an extended flexible conformation which contains, however, a local non-random spatial structure involving the fragment--Phe-22--Val-23--Gln-24--Trp-25--. This local conformation is preserved in the partial sequence 22--26 and could thus be characterized in detail. Two interesting conclusions resulted from these experiments. One is that the local spatial structure in the fragment 22--25 of glucagon is identical to that observed in the fragment 20--23 of the human parathyroid hormone. Secondly, the backbone conformation in the C-terminal fragment of glucagon in solution must be different from the alpha-helical structure observed in single crystals of glucagon. These new structural data are analyzed with regard to relationships with glucagon binding to the target cells.