Characterisation of a Local Structure in the Synthetic Parathyroid Hormone Fragment 1‐34 by 1H Nuclear‐Magnetic‐Resonance Techniques

Abstract

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‐Gln‐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 α and γ 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%. Copyright © 1978, Wiley Blackwell. All rights reserved