Teriparatide: Molecular Structure

Molecular Structure and Properties#

Teriparatide is a 34-amino-acid recombinant peptide identical to the N-terminal fragment of human parathyroid hormone (PTH(1-34)). It has a molecular weight of 4,117.8 Da, molecular formula C181H291N55O51S2, and CAS number 52232-67-4. Unlike synthetic peptide analogs, teriparatide is produced by recombinant DNA technology in Escherichia coli and has an identical sequence to native human PTH(1-34).

Amino Acid Sequence#

The complete 34-amino-acid sequence of teriparatide:

Ser-Val-Ser-Glu-Ile-Gln-Leu-Met-His-Asn-Leu-Gly-Lys-His-Leu-Asn-Ser-Met-Glu-Arg-Val-Glu-Trp-Leu-Arg-Lys-Lys-Leu-Gln-Asp-Val-His-Asn-Phe

(SVSEIQLMHNLGKHLNSMERVEWLRKKLQDVHNF in single-letter code)

This sequence represents the first 34 of the 84 amino acids of full-length PTH. The N-terminal (1-34) region contains the complete biological activity of the hormone, as demonstrated by the fact that PTH(1-34) has equivalent potency to PTH(1-84) at the PTH1 receptor.

Key structural and functional domains:

• Positions 1-6 (SVSEIQL): N-terminal activation domain. Critical for receptor activation and cAMP signaling. Truncation of even 2 N-terminal residues dramatically reduces biological activity.
• Position 8 (Met): Methionine residue susceptible to oxidation; oxidized teriparatide has reduced biological activity, informing storage requirements.
• Positions 15-34: Receptor binding domain. This amphipathic alpha-helical region mediates high-affinity binding to the extracellular domain of PTH1R. The helical structure is essential for receptor engagement.
• Position 34 (Phe): C-terminal phenylalanine. The 34-residue fragment was selected as the minimum length retaining full receptor binding affinity and biological activity.
• Two methionine residues (positions 8 and 18): Both are susceptible to oxidation, which can reduce potency. This informs the requirement for refrigerated storage.

PTH1 Receptor Binding#

Teriparatide binds PTH1R in a two-step process:

1. Binding step: The C-terminal alpha-helical domain (residues 15-34) engages the extracellular domain of PTH1R with high affinity
2. Activation step: The N-terminal domain (residues 1-14) inserts into the transmembrane domain of the receptor, triggering conformational changes that activate G protein signaling

Teriparatide binds both the RG (G protein-coupled) and R0 (ligand-independent) conformational states of PTH1R. The R0 interaction produces more prolonged cAMP signaling compared to agents that preferentially bind RG (such as abaloparatide), which may explain teriparatide's higher hypercalcemia rates and its effects on both bone formation and resorption.

Physicochemical Properties#

Teriparatide is formulated as a clear, colorless liquid for subcutaneous injection in a pre-filled pen device.

Formulation (Forteo pen): Each pen contains 2.4 mL of solution with teriparatide 250 mcg/mL (600 mcg total), glacial acetic acid, sodium acetate (anhydrous), mannitol, metacresol, and water for injection. Each pen delivers 28 daily doses of 20 mcg.

• Solubility: Freely soluble in aqueous solution at acidic to neutral pH
• Stability: Sensitive to oxidation at methionine residues; requires refrigerated storage
• Secondary structure: Alpha-helical conformation in the C-terminal domain (residues 15-34) is critical for receptor binding

Pharmacokinetics#

Teriparatide has rapid absorption and short systemic exposure following subcutaneous injection, producing the transient pulsatile PTH1R activation essential for its anabolic mechanism.

Absorption: After subcutaneous injection of 20 mcg, teriparatide reaches peak plasma concentration (Cmax) of approximately 35 pg/mL within 30 minutes (median Tmax approximately 30 minutes). Bioavailability is approximately 95%.

Distribution: Volume of distribution is approximately 0.12 L/kg (approximately 8.4 L for a 70 kg person), indicating distribution primarily within the extracellular fluid.

Metabolism: Teriparatide is degraded by non-specific proteolytic enzymes in the liver and kidneys, consistent with PTH catabolism. It does not undergo CYP-mediated metabolism.

Elimination: The terminal half-life is approximately 1 hour following subcutaneous administration (approximately 5 minutes following intravenous administration, reflecting rapid proteolytic clearance). Systemic clearance is approximately 62 L/hr in women and 94 L/hr in men.

Structural Comparison with Related Peptides#

• vs. Abaloparatide (PTHrP analog): Abaloparatide is based on the PTHrP(1-34) sequence with 8 C-terminal substitutions, showing 41% homology to teriparatide. Abaloparatide preferentially binds RG, producing more transient signaling with lower hypercalcemia rates and potentially greater cortical bone gains.
• vs. PTH(1-84) (Natpara): Full-length PTH has additional C-terminal domains (35-84) that may have independent biological effects on calcium-phosphate metabolism. PTH(1-84) was marketed as Natpara for hypoparathyroidism but was withdrawn due to device issues.
• vs. PTHrP(1-34): Native PTHrP has distinct receptor binding kinetics from PTH, with preferential RG binding. Abaloparatide was engineered from this scaffold.

Related Reading#

• Teriparatide overview and research guide
• Peptides similar to Teriparatide
• Teriparatide research evidence