Death Receptor 5 Activation Is Energetically Coupled to Opening of the Transmembrane Domain Dimer

Area of Science:

• Biophysics
• Molecular Biology
• Cell Signaling

Background:

• The precise mechanism of signal transduction by tumor necrosis factor (TNF) receptors upon ligand binding remains unclear.
• Activation of some TNF receptors, like Death Receptor 5 (DR5), is proposed to involve a scissor-like opening of their transmembrane (TM) dimer.
• Understanding this TM domain transition is key to elucidating receptor activation pathways.

Purpose of the Study:

• To provide direct biophysical evidence for the opening of DR5 TM-dimers upon ligand binding.
• To investigate the energetic landscape of the TM domain transition using computational and experimental approaches.
• To determine the role of TM domain dimer interface mutations in receptor activation and cellular response.

Main Methods:

• Time-resolved fluorescence resonance energy transfer (TR-FRET) to monitor TM-dimer separation in real-time.
• All-atom molecular dynamics (MD) simulations of the isolated TM domain in lipid bilayers.
• Thermodynamic potential of mean force (PMF) calculations to determine energy barriers.
• Site-directed mutagenesis (alanine to phenylalanine) of the TM domain dimer interface.
• Cell-based death assays to assess receptor sensitivity.

Main Results:

• Direct biophysical evidence confirmed that DR5 TM-dimers open in response to ligand binding.
• Computational simulations predicted that specific mutations at the TM dimer interface alter the energy landscape of opening.
• Single point mutations partially destabilized the closed conformation but did not eliminate the opening barrier.
• A double mutation at the center of the TM dimer interface was predicted to eliminate the opening barrier and stabilize the open state.
• Experimental validation showed that the double mutant significantly increased TM-dimer separation and enhanced cellular sensitivity to ligand stimulation.

Conclusions:

• Ligand binding induces a conformational change involving the opening of the Death Receptor 5 transmembrane dimer.
• The transmembrane domain dimer interface plays a critical role in the energetics of receptor activation.
• Targeted mutations can modulate the TM domain opening process, impacting receptor sensitivity and downstream signaling.
• This study provides a mechanistic link between TM domain dynamics and TNF receptor signaling efficacy.