Functional anatomy of an allosteric protein

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Synaptic receptors, such as nicotinic acetylcholine receptors (nAChRs), are crucial allosteric proteins regulating cell signaling.
• Understanding the precise mechanisms of receptor gating, or conformational change, is vital for comprehending neuronal communication.

Purpose of the Study:

• To quantitatively map the energy landscape of the gating conformational change in a nicotinic acetylcholine receptor.
• To identify key regions and energy transitions involved in the allosteric regulation of receptor function.

Main Methods:

• Single-channel electrophysiology was employed to measure and map energy changes during receptor gating.
• Analysis focused on identifying regions with the earliest conformational changes (high ϕ-values) and significant energy fluctuations.

Main Results:

• The transmitter-binding sites and αM2-αM3 linkers in the α-subunits exhibited the highest ϕ-values, indicating they change conformation earliest.
• Significant gating-energy changes were observed at the transmitter-binding sites, α-subunit interfaces, αM1 helix, and the gate.
• The hydrophobic gate appears to unlock in a stepwise manner (three steps).

Conclusions:

• Rearrangements of the αM2-αM3 linkers are hypothesized to trigger the global allosteric transition.
• The gating process is not solely a mechanical event driven by agonist binding affinity, suggesting a more complex interplay of forces.