Characterisation of a local structure in the synthetic parathyroid hormone fragment 1--34 by 1H nuclear-magnetic-resonance techniques.

Previous studies had shown that the molecular conformation of the synthetic human parathyroid hormone fragment 1--34 in dilute aqueous solution contained a local non-random structure formed by the four consecutive residues--Val-21--GIn-22--Trp-23--Leu-24--. This paper gives a detailed description of this local spatial structure obtained from high resolution 1H NMR studies at 360 MHZ of several peptide analogs of the partial sequence 20--24. The most important spectral parameters were high-field shifts of the alpha and gamma protons of Val-21, the spin-spin coupling constants related to the rotamer populations of the side-chains of Val-21 and Trp-23, and pH titration shifts of the amide proton resonances. It was found that the backbone fragment 20--24 is so arranged that the side-chain of Val-21 is located next to the indole ring plane of Trp-23; evidence is presented that this non-random structure is mainly stabilized by hydrophobic interactions between the side-chains of Val-21 and Trp-23. The thermal population of the observed molecular structure at room temperature was estimated from the nuclear magnetic resonance data to be approximately 20%.

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.