Assessment by 1H NMR Spectroscopy of the Structural Behaviour of Human Parathyroid-Hormone-Related Protein(1 - 34) and Its Close Relationship with the N-Terminal Fragments of Human Parathyroid Hormone in Solution

Human parathyroid-hormone-related protein (hPTHrP) is a hormone that is over-expressed by a large number of tumors and is produced by a variety of normal cells. Its main biological functions are shown by the N-terminal fragment (1-34) and are similar to those of parathyroid hormone with which it shares a common G-protein-coupled receptor. Hence to gain insight into the structure-function relationship of these hormones we have investigated the solution structure of hPTHrP(1-34) in pure water alone and have monitored the effect of adding TFE. CD spectra in pure water showed that it only possesses a small content of alpha-helical secondary structure, which from the NMR data, consists of a short unstable helix between Gln-16 and Leu-24 with the rest of the peptide in an essentially unstructured state. On adding 50% TFE (v/v) there was a considerable increase in stable secondary structure, without any evidence of stable tertiary structure. The subsequent structure calculations showed the presence of two well defined helices, from Ser-3 to Gly-12 and from Asp-17 to Thr-33, connected by a flexible linker. The similarity in behaviour of hPTHrP(1-34) and the N-terminal fragments of PTH under various solution conditions is shown from the 1H NMR data presented here and an extensive review of the literature data.