Deletion of lysine 13 alters the structure and function of parathyroid hormone

Inactivation of parathyroid hormone: perspectives of drug discovery to combating hyperparathyroidism

Hormonal coordination is tightly regulated within the human body and thus regulates human physiology. The parathyroid hormone (PTH), a member of the endocrine system, regulates the calcium and phosphate level within the human body. Under non-physiological conditions, PTH levels get upregulated (hyperparathyroidism) or downregulated (hypoparathyroidism) due to external or internal factors. In the case of hyperparathyroidism, elevated PTH stimulates cellular receptors present in the bones, kidneys, and intestines to increase the blood calcium level, leading to calcium deposition. This eventually causes various symptoms including kidney stones. Currently, there is no known medication that directly targets PTH in order to suppress its function. Therefore, it is of great interest to find novel small molecules or any other means that can modulate PTH function. The molecular signaling of PTH starts by binding of its N-terminus to the G-protein coupled PTH1/2 receptor. Therefore, any intervention that affects the N-terminus of PTH could be a lead candidate for treating hyperparathyroidism. As a proof-of-concept, there are various possibilities to inhibit molecular PTH function by (i) a small molecule, (ii) N-terminal PTH phosphorylation, (iii) fibril formation and (iv) residue-specific mutations. These modifications put PTH into an inactive state, which will be discussed in detail in this review article. We anticipate that exploring small molecules or other means that affect the N-terminus of PTH could be lead candidates in combating hyperparathyroidism.

Lysine nutrition in swine and the related monogastric animals: muscle protein biosynthesis and beyond

Improving feed efficiency of pigs with dietary application of amino acids (AAs) is becoming increasingly important because this practice can not only secure the plasma AA supply for muscle growth but also protect the environment from nitrogen discharge with feces and urine. Lysine, the first limiting AA in typical swine diets, is a substrate for generating body proteins, peptides, and non-peptide molecules, while excess lysine is catabolized as an energy source. From a regulatory standpoint, lysine is at the top level in controlling AA metabolism, and lysine can also affect the metabolism of other nutrients. The effect of lysine on hormone production and activities is reflected by the change of plasma concentrations of insulin and insulin-like growth factor 1. Lysine residues in peptides are important sites for protein post-translational modification involved in epigenetic regulation of gene expression. An inborn error of a cationic AA transporter in humans can lead to a lysinuric protein intolerance condition. Dietary deficiency of lysine will impair animal immunity and elevate animal susceptibility to infectious diseases. Because lysine deficiency has negative impact on animal health and growth performance and it appears that dietary lysine is non-toxic even at a high dose of supplementation, nutritional emphasis should be put on lysine supplementation to avoid its deficiency rather than toxicity. Improvement of muscle growth of monogastric animals such as pigs via dietary lysine supply may be due to a greater increase in protein synthesis rather than a decrease in protein degradation. Nevertheless, the underlying metabolic and molecular mechanisms regarding lysine effect on muscle protein accretion merits further clarification. Future research undertaken to fully elucidate the metabolic and regulatory mechanisms of lysine nutrition could provide a sound scientific foundation necessary for developing novel nutritional strategies to enhance the muscle growth and development of meat animals.

Stabilized NMR structure of human parathyroid hormone(1-34)

The structure of the biologically-active N-terminal region of human parathyroid hormone, PTH(1-34), was investigated in the presence of 10% trifluoroethanol using two-dimensional proton NMR spectroscopy, distance geometry and dynamic simulated annealing. Complete assignments of all backbone and side chain hydrogens were made with the aid of totally correlated spectroscopy (TOCSY) experiments, providing through-bond 1H-1H connectivities, and NOESY providing through-space and sequential backbone connectivities. Distance and angle constraints were used in the distance geometry algorithm DIANA II to generate a family of structures satisfying all inputs. The lowest energy structures were further refined using the dynamic-simulated-annealing protocol XPLOR 3. The major structural features evident in 10% trifluoroethanol are two segments of alpha-helix extending from residues Glu4 to Lys14/His14 and Ser17 to Asp30. A short length of unordered structure joined the two spans of helix. The structures of the N-terminal regions (4-13/14) agreed closely with the structure found in human parathyroid-hormone-related protein (PTHrP)(1-34) obtained earlier by Ray, Barden and Kemp [19]. However, PTHrP(16-19) exhibited a reverse turn which is incorporated in an extended helix in PTH. The consequent interactions between several hydrophobic residues in the C-terminal region in PTHrP are absent in PTH. Moreover, the turn in PTHrP(22-25) at the start of the C-terminal helix is present as a more standard loop of helix in PTH. Comparisons between the structures of the two hormones has enabled the probable location and structure of the PTH receptor-binding site to be placed in the segment of amphiphilic alpha-helix (24-31).

Properties of amino-terminal parathyroid hormone-related peptides modified at positions 11-13

Biological properties of amino-terminal PTHrP analogues modified in the region 11-13 were examined using ROS 17/2.8 cells. [Leu11,D-Trp12,Arg13,Tyr36]PTHrP(1-36)amide had a 17-fold lower binding affinity for the receptor (apparent Kd: 5 x 10(-8) M) than [Tyr36]PTHrP(1-36)amide or [Arg11,13,Tyr36]PTHrP(1-36)amide (apparent Kd for both: 2 x 10(-9) M). Moreover, it is only a weak partial agonist despite completely inhibiting radioligand binding. [Leu11,D-Trp12,Arg13,Tyr36,Cys38]PTHrP(7-3 8) and PTHrP(7-34)amide had similar receptor affinities (apparent Kds: 5 x 10(-8) M and 8 x 10(-8) M), while that of [Nle8,18,Tyr34]bPTH(7-34)amide was more than 10-fold lower (apparent Kd: 2 x 10(-6) M). These changes in biological properties suggest that high affinity receptor binding requires both amino- and carboxyl-terminal domains of the PTHrP(1-36) sequence and/or intramolecular interactions which are impaired by the D-Trp substitution for Gly12.

Parathyroid hormone stimulates formation of inositol phosphates in a membrane preparation of canine renal cortical tubular cells

Recent studies have shown that, in addition to its well-known action to stimulate adenylate cyclase activity, parathyroid hormone (PTH) may stimulate the inositol phosphate second messenger system in its target tissues, bone and kidney. We have developed a membrane preparation of canine renal cortex to test this hypothesis. We also have examined the potential role of guanine nucleotides on the formation of inositol phosphates (IPs) in this tissue. Collagenase-dispersed tubules were labeled with [3H]inositol, and membranes containing labeled phospholipase C (PLC) substrates ([3H]phosphatidyl inositol, [3H]phosphatidylinositol monophosphate, and [3H]phosphatidylinositol bisphosphate) were prepared. bPTH-(1-34) (100 nM) rapidly increased levels of all measured [3H]IPs (IP1, IP2, and IP3) 1.6-1.7-fold within the first 30 s of stimulation. The half-maximal concentration for the response to bPTH-(1-34) was approximately 8 nM. GTP gamma S (100 microM), a nonhydrolyzable analog of GTP, also increased levels of the three [3H]IPs (1.8 to 2.8-fold). The half-maximal concentration for the response to GTP gamma S was approximately 30 microM. In the presence of GTP gamma S, bPTH-(1-34) increased levels of IPs by up to 2.7 times more than GTP gamma S alone. The results indicate that bPTH-(1-34) can stimulate the formation of inositol phosphates in the kidney and suggest that PTH may activate a receptor coupled to this effect through a guanine nucleotide regulatory protein.

Two-dimensional 1H-NMR study of the 1-34 fragment of human parathyroid hormone

The complete assignment of resonances in the proton nmr spectrum of the 1-34 amino acid fragment of human parathyroid hormone [hPTH(1-34)], determined using a combination of one- and two-dimensional nmr techniques at 500 MHz, is described. In particular, homonuclear Hartmann-Hahn experiments, recorded in H2O and D2O, are used to resolve ambiguities in the connectivities between the highly overlapped resonances in the aliphatic region of the spectrum. One-dimensional multiple quantum filtering experiments are used to identify serine and phenylalanine spin systems. Analyses of the through-bond and through-space connectivities in the alpha H-NH fingerprint regions of the correlated spectroscopy (COSY) and nuclear Overhauser effect spectroscopy (NOESY) spectra lead to the assignment of resonances to specific amino acid residues in the polypeptide. Examination of the observed NOE cross peaks indicates that hPTH(1-34) has no detectable secondary structural elements in aqueous solution.