Protein engineering of a novel constitutively active hormone-receptor complex

Area of Science:

• Molecular Endocrinology
• Protein Engineering
• G Protein-Coupled Receptor Signaling

Background:

• Human chorionic gonadotropin (hCG) is a critical glycoprotein hormone.
• hCG signals through a specific G protein-coupled receptor (GPCR).
• GPCRs mediate cellular responses via second messengers like cAMP.

Purpose of the Study:

• To engineer and characterize a novel single-chain molecule linking hCG and its receptor.
• To investigate the functional consequences of covalently linking a hormone to its receptor.
• To determine the binding and signaling properties of the engineered hCG-receptor complex.

Main Methods:

• Genetic engineering of a single polypeptide chain incorporating the hCG ligand and its receptor.
• Expression of the engineered construct in transfected cells.
• Assessment of exogenous hCG binding, protease cleavage effects, and intracellular cAMP levels.

Main Results:

• Cells expressing the single-chain hCG-receptor construct showed limited binding of exogenous hCG.
• Site-specific protease cleavage of the linked hormone restored receptor accessibility to exogenous hCG.
• The engineered construct exhibited elevated basal cAMP levels, indicating constitutive activity, with no further stimulation by exogenous hCG.

Conclusions:

• A covalently linked single-chain hCG-receptor complex forms a stable and constitutively active signaling unit.
• This engineered system provides insights into GPCR activation mechanisms.
• The findings suggest potential for novel therapeutic strategies involving engineered hormone-receptor interactions.