Negative antagonists promote an inactive conformation of the beta 2-adrenergic receptor

Area of Science:

• Pharmacology
• Molecular Biology
• Biochemistry

Background:

• The beta 2-adrenergic receptor (β2AR) exists in equilibrium between inactive (R) and active (R*) conformations.
• Adrenergic agonists and specific mutations can promote the R* state, leading to receptor activation.

Purpose of the Study:

• To identify beta-adrenergic receptor antagonists that inhibit basal β2AR signaling.
• To characterize the molecular properties of negative antagonists acting on the β2AR.

Main Methods:

• Screening of beta-adrenergic receptor-blocking drugs for inhibition of basal β2AR signaling.
• Affinity measurements for the inactive receptor conformation.
• Assays to detect the formation of beta-adrenergic receptor kinase (βARK) substrates.

Main Results:

• ICI 118551 and betaxolol were identified as negative antagonists, reducing basal β2AR activity.
• ICI 118551 exhibits higher affinity for the inactive R state.
• ICI 118551 inhibits the spontaneous formation of βARK substrates by the receptor.

Conclusions:

• Negative antagonists like ICI 118551 stabilize the inactive R conformation of the β2AR.
• These findings reveal a reciprocal mechanism to agonists, where negative antagonists promote receptor inactivation.