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 'H 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 a and y 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%.In a previous paper it was shown that the synthetic human parathyroid hormone fragment 1 -34 exists in aqueous solution predominantly in a flexible extended form, where, however, a local non-random structure was also clearly manifested in the ' H nuclear magnetic resonance (NMR) parameters [l]. This non-random conformation was then found to involve the amino acid residues -Val-21 -Gln-22-Trp-23 -Leu-24 -, and it was demonstrated that the same structure was preserved in the pentapeptide Arg-Val-Gln-Trp-Leu[l]. Our interest in this structure was further enhanced, since the tetrapeptide sequence 21 -24 in the parathyroid hormone corresponds to the tetrapeptide sequence 23 -26 in glucagon [2,3]. The present paper describes a detailed investigation of the spatial arrangement of the tetrapeptide segment 21 -24 in the parathyroid hormone 1 -34.The strategy used for this study was to compare the spatial structures of different synthetic peptide analogs by high-resolution 'H NMR techniques. On the basis of the requirements of compatibility with all the NMR data and with the criteria of closest interAbhreviations. NMR, nuclear magnetic resonance; parathyroid hormone 1 -34, synthetic N-terminal fragment 1 -34 of the human parathyroid hormone. atomic distances, a molecular model for the tripeptide segment -Val-21 -Gln-22 -Trp-23 -in the parathyroid hormone 1 -34 was constructed. With the use of the atomic coordinates obtained from this model, the thermal population of the local spatial structure was estimated in a quantitative analysis of the NMR data. MATERIALS AND METHODS Peptidr SynthesisThe synthesis of parathyroid hormone 1-34 according to the sequence determined by Brewer et al. [4] and of several partial sequences thereof was described previously [ 5 ] . This concerns in particular the partial sequences Met-1

Solvent-accessibility of discrete residue positions in the polypeptide hormone glucagon by 19F-NMR observation of 4-fluorophenylalanine

“…This is clearly documented by comparison of the 19 F-NMR spectra of [4F-Phe6,22]-glucagon in H 2 O and DMSO (Fig. 1b); it has been shown previously that DMSO reversibly unfolds the hydrophobic cluster formed by the glucagon residues 22–25 (Boesch et al 1978; Bundi et al 1978). It will be interesting to investigate interactions of [4Phe6,22]-glucagon with GCGR not only on the basis of solvent accessibility and line shape variations due to decreased mobility of the bound glucagon and possibly conformational microheterogeneity, but also on the basis of the chemical shifts, which may provide information on conformational changes of the glucagon upon binding.…”

A theoretical study of the structure of parathyroid hormone.

“…From NMR data, Bundi et al. (14) suggested that in PTH the side chains of and Trp-23 are in close proximity. They proposed a form of y-helix for this region of the molecule, which would create a sharp twist in the chain at this point.…”

“…The "hydrophobic arcs" are outlined. (B) Helical wheel diagram for segment 15-25 with a three-residue segment of helix (residues 21-23) in y-helical form as proposed by Bundi et al (14). Dotted lines identify the residues whose position in the wheel is altered by this modification.…”

Comparative Study of Chicken and Human Parathyroid Hormone‐(1–34)‐Peptides in Solution with SDS

“…One-dimensional and two dimensional NMR studies on hPTH-(1 -34) demonstrated that it predominantly assumes an extended and flexible structure with the only ordered region of residues being 20-24 (Bundi et al, 1976(Bundi et al, , 1978Lee and Russell, 1989). For bPTH-(1-34), a small amount of secondary structure was postulated from observed spectral changes as a function of pH (Smith et al, 1987).…”