Expression and characterization of a recombinant human parathyroid hormone partial agonist with antagonistic properties: Gly-hPTH(-1-->+84)

High yield production of recombinant native and modified peptides exemplified by ligands for G-protein coupled receptors

G-protein coupled receptors (GPCRs) comprise a large family of membrane proteins and attract pharmaceutical interest as therapeutic targets. Two examples of class B GPCRs that are involved in metabolic diseases are the Parathyroid hormone receptor 1 (PTHR1) and the Glucagon-like-peptide-1 receptor (GLP-1R) which play central roles in osteoporosis and diabetes mellitus type II, respectively. Class B GPCRs are characterised by a large extracellular N-terminal domain with a typical disulfide bridge pattern. This domain is responsible for the binding of peptide hormone ligands. Here we report the recombinant expression of these ligands in natural and several modified forms for their use in functional assays, NMR analyses or affinity purification of receptor/ligand complexes for crystallisation. Applying the SUMO system, low cost expression of soluble fusion-proteins is achieved. Moreover, via the SUMO cleavage site, the authentic N-terminal sequence which is essential for ligand-receptor interactions can be obtained. Purification of the peptide by RP-HPLC results in >98% pure preparations. The strategy can also be adopted for many other purposes, especially if small peptides are needed at either large amounts or with specific features like isotope, affinity or fluorescent labels. Furthermore, for the growing demand for therapeutic peptides, this method could represent a straightforward production process.

Binding and cyclic AMP stimulation by N-terminally deleted human PTHs (3-84 and 4-84) in a homologous ligand receptor system

We have produced in yeast two human parathyroid hormone (hPTH) analogs with amino-terminal deletions, hPTH(3-84) and hPTH(4-84), employing the mating factor alpha (MF alpha) expression system. The authenticity of the polypeptides was demonstrated by amino-terminal analysis, amino acid composition, and molecular mass analysis. In cells (LLC-PK1) transfected with the human PTH/parathyroid hormone-related protein (PTHrP) receptor, using [125I-Tyr36]chickenPTHrP(1-36)NH2 as radioligand, binding studies revealed dissociation constants at equilibrium (Kd) for hPTH(3-84) and hPTH(4-84) of 4.7 and 8.0 nM, respectively, only slightly higher than natural recombinant hPTH(1-84) Kd = 2.3 nM). In comparison, [Nle8,18,Tyr34]bovinePTH(3-34)NH2 and [Tyr36]cPTHrP(1-36)NH2 showed equal Kd's of 1.9 nM. Neither of the N-terminally deleted hPTH analogs showed any detectable stimulation of cAMP production in the cells at concentrations below 20 nM. At supersaturated concentrations (500 nM) with receptor occupancy of more than 95% these hPTH analogs revealed about 15% rest agonism compared with that of hPTH(1-84). hPTH(1-84) and [Tyr36]cPTHrP(1-36)NH2 showed an equal half maximal cyclic adenosine monophosphate (cAMP) stimulation of about 0.8 and 0.7 nM, respectively. The hPTH analogs did not show any ability to antagonize cellular cAMP production induced by either hPTH or [Tyr36]cPTHrP(1-36)NH2. [Nle8,18,Tyr34]bPTH(3-34)NH2 did also not antagonize cAMP stimulation by hPTH, but inhibited [Tyr36]cPTHrP(1-36)NH2-induced cAMP production by 40% when present at a 1000 M excess. These distinct results related to PTH and PTHrP from different species are important to consider in experiments evaluating potential hPTH or PTHrP antagonism, and employment of a hPTH/PTHrP receptor model is a requirement.