A conserved protonation-induced switch can trigger "ionic-lock" formation in adrenergic receptors

Area of Science:

• Molecular biology
• Biochemistry
• Computational chemistry

Background:

• G-protein-coupled receptors (GPCRs) are critical for cellular signal transduction.
• The precise molecular mechanisms governing GPCR activation remain incompletely understood.
• Understanding GPCR signaling is vital for drug discovery and therapeutic development.

Purpose of the Study:

• To elucidate the molecular dynamics underlying signal transduction in GPCRs.
• To identify key residues and interactions involved in the transition between active and inactive GPCR states.
• To investigate the role of conserved residues in modulating GPCR activity.

Main Methods:

• Submicrosecond molecular dynamics simulations of beta-adrenergic receptors.
• Analysis of residue cooperation and network dynamics.
• Investigation of protonation states and their impact on receptor conformation.

Main Results:

• Cooperation among conserved residues is essential for shifting the equilibrium between active and inactive GPCR states.
• Formation of an 'ionic-lock' is directly correlated with the protonation of a conserved aspartic acid residue [Asp(2.50)], despite significant distance.
• Internal polar residues act as microswitches, transmitting signals from Asp(2.50) to the G-protein binding site.

Conclusions:

• Conserved residues play a critical role in GPCR signal transduction through coordinated action.
• The protonation state of Asp(2.50) is a key determinant of the 'ionic-lock' and receptor activation.
• Evolutionary differences in GPCR structure explain variations in constitutive activity, particularly between opsin and non-opsin receptors.