STRUCTURE OF HUMAN PARATHYROID-HORMONE-1-37 IN SOLUTION

Human parathyroid hormone (hPTH), amino acids Ser(1) to Leu(37), is biologically active with respect to both receptor binding and activation of adenylate cyclase to influence the serum calcium concentration. It induces DNA synthesis via an unknown signal pathway. We investigated the structure of hPTH(1-37) in H2O/buffer solution under near physiological conditions, that is pH 6.0 and 270 mM salt, by circular dichroism, ultracentrifugation, nuclear magnetic resonance spectroscopy, and molecular dynamics calculations. Complete sequence specific assignments of all H-1 resonances were performed by using H-1 two-dimensional NMR measurements (double quantum-filtered correlated spectroscopy, nuclear Overhauser effect spectroscopy (NOESY), and total correlation spectroscopy with suppression of NOESY-type cross-peaks spectra). hPTH(1-37) obtained helical structure and showed hydrophobic interactions defining a tertiary structure. The NH2-terminal four amine acids of hPTH(1-37) did not show a stable conformation. Evidence for an alpha-helical region between IIe(5) and Asn(10) was found. This region was followed by a flexible link (Gly(12), Lys(13)) and a well defined turn region, His(14) to Ser(17). The latter was stabilized by hydrophobic interactions between Trp(23) and Leu(15). Ser(17) through at least Leu(28) formed an alpha-helix. Arg(20) and Lys(27) were involved in the core built by His(14) to Ser(17). Unrestrained molecular dynamics simulations indicated that the structure was stable on the 200 ps time scale.