Full-length chicken parathyroid hormone. Biosynthesis in Escherichia coli and analysis of biologic activity

Evolution of the parathyroid hormone family and skeletal formation pathways

Bone is considered to be a feature of higher vertebrates and one of the features that was required for the movement from water onto land. But there are a number of evolutionarily important species that have cartilaginous skeletons, including sharks. Both bony and cartilaginous fish are believed to have a common ancestor who had a bony skeleton. A number of factors and pathways have been shown to be involved in the development and maintenance of bony skeleton including the Wnt pathway and the parathyroid hormone gene family. The study of these pathways and factors in cartilaginous animals may shed light on the evolution of the vertebrate skeleton.

Regulation of transepithelial phosphate transport by PTH in chicken proximal tubule epithelium

The effect of parathyroid hormone (PTH) and activation of protein kinase C (PKC) and protein kinase A (PKA) on transepithelial P(i) transport was examined in monolayers of chick proximal tubule cells in primary culture (PTCs). Acute exposure of the PTCs to PTH (10(-9) M, basolateral side) significantly decreased the net reabsorption of P(i) by approximately 66%. There was no effect after the addition of PTH to the luminal side. Activation of PKC by phorbol 12-myristate 13-acetate (PMA; 0.1 microM) dramatically decreased net P(i) reabsorption by approximately 60%. Bisindolylmaleimide I (BIM; 1 microM), a highly selective PKC inhibitor, prevented PMA-induced inhibition. Activation of adenylate cyclase/PKA by forskolin (10 microM) mimicked the effect of PTH by significantly reducing net P(i) reabsorption by one-half. Addition of H-89 (10 microM), a potent inhibitor of PKA, abolished forskolin-induced inhibition. PTH inhibition was blocked by either BIM or H-89. Tissue electrophysiology remained stable after all treatments. There was a decreased immunoreactivity of the luminal Na+-P(i) cotransporter NaPi-IIa after PTH treatment. These data indicate that PTH inhibition of P(i) reabsorption in this in vitro system is mediated by PKC and PKA.

Specificity of factor Xa in the cleavage of fusion proteins

The precursor protein honey bee prepromelittin has been expressed as a fusion protein in Escherichia coli joined to the C-terminus of a truncated form of the bacteriophage gene 10 protein via an engineered recognition sequence for Factor Xa. Factor Xa was found to cleave poorly at the engineered site, giving a low yield of the required prepromelittin. In contrast, cleavage on the C-terminal side of the sequence VLGR at residue 67 in the gene 10 sequence proceeded in high yield. Factor Xa may be inhibited by adjacent hydrophobic sequences on the C-terminal side of a potential cleavage site.

The cellular and molecular regulation of 1,25(OH)2D3 production

The synthesis of 1,25(OH)2D3 is a critical control point in the regulation of calcium metabolism, and possibly in the growth and differentiation of a number of cell types. This paper reviews our current understanding of the regulation of this process at the cellular and molecular levels, with the emphasis on the mechanisms of feedback control 1,25(OH)2D3 itself, control of parathyroid hormone, the roles of cyclic AMP dependent protein kinase and protein kinase C, and the interaction between the various intracellular regulators of 1,25(OH)2D3 production.

Expression of honeybee prepromelittin as a fusion protein in Escherichia coli

Strategies for the expression of precursors of eukaryotic secreted proteins as part of fused proteins in Escherichia coli have been explored. A fusion protein with beta-galactosidase at the N-terminal end and honeybee prepromelittin at the C-terminal end (beta-gal-pM) was expressed in low amounts as a cleaved polypeptide, from which the promelittin portion had been removed. Inclusion in the induction culture of 10 mM MgCl2 or 8.3% (v/v) ethanol, inhibitors of signal peptidase, gave rise to the full-length beta-gal-pM fusion protein. The results suggest that a soluble recombinant fusion protein with a signal peptide in an internal location 660 residues from the N-terminus is recognized by the E. coli translocation apparatus in the inner membrane and by leader peptidase. High-level production (about 45% of total cellular proteins) of prepromelittin was achieved when it was part of a fusion protein at the C-terminus of a truncated insoluble polypeptide from bacteriophage gene 10. This fusion protein separated into inclusion bodies in an aggregated form. In contrast, attempts to express prepromelittin by itself or at the N-terminal end of a fusion with mouse dihydrofolate reductase (pM-DHFR) proved unsuccessful.