SRP RNA controls a conformational switch regulating the SRP-SRP receptor interaction

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Co-translational protein targeting to membranes is essential for cellular function.
• The signal-recognition particle (SRP) and its receptor (SR) mediate this process through their GTPase domains and N-terminal domains.
• SRP-SR complex formation is typically slow without SRP's RNA component.

Purpose of the Study:

• To investigate the role of the N-terminal four-helix bundles (N domains) in SRP-SR complex formation.
• To elucidate the mechanism by which SRP RNA catalyzes SRP-SR interaction.

Main Methods:

• Protein engineering: Truncation of helix N1 in SRP and SR.
• Biochemical assays: Measuring interaction rates of truncated SRP and SR.
• Biophysical techniques: NMR spectroscopy to analyze conformational changes.
• Enzyme kinetics: Assessing GTPase activity.

Main Results:

• Truncation of helix N1 in both SRP and SR dramatically accelerated their interaction rate.
• Truncated SRP and SR interacted at a rate comparable to RNA-catalyzed interaction, even without RNA.
• NMR and GTPase activity analyses indicated that helix N1 truncation in SR mimics the RNA-induced conformational switch.

Conclusions:

• The N-terminal helices of SRP and SR act as autoinhibitory elements for complex formation in the absence of SRP RNA.
• This autoinhibition provides a mechanism for SRP RNA to regulate and coordinate the SRP-SR interaction.
• Understanding this regulation is crucial for comprehending co-translational protein targeting.