Co-Translational Membrane Targeting and Holo-Translocon Docking of Ribosomes Translating the SRP Receptor

Area of Science:

• * Molecular Biology
• * Cell Biology
• * Biochemistry

Background:

• * Integral membrane protein synthesis relies on translocon-associated ribosomes.
• * The signal recognition particle (SRP) and its receptor (FtsY) mediate ribosome assembly on translocons.
• * Early membrane targeting mechanisms of FtsY remain unclear.

Purpose of the Study:

• * To elucidate the in vivo membrane targeting pathway of FtsY.
• * To identify initial docking sites and interactions of FtsY.
• * To propose a model for co-translational FtsY membrane targeting.

Main Methods:

• * In vivo experiments using stalled FtsY translation intermediates.
• * Pull-down assays to identify associated proteins.
• * Site-directed cross-linking to map interactions.
• * Translocon over-expression studies.

Main Results:

• * Identified FtsY-nascent chain-associated proteins in the cytosol and on the membrane.
• * Demonstrated interactions between FtsY-translating ribosomes, cytosolic chaperones, and the translocon.
• * Showed that translocon over-expression enhances membrane association of FtsY-translating ribosomes.
• * Revealed distinct co-translational and post-translational contacts of FtsY nascent chains with the translocon.

Conclusions:

• * FtsY targets the membrane co-translationally through interactions with chaperones and the translocon.
• * Translocon docking follows initial cytosolic chaperone interactions.
• * Co-translational FtsY-translocon contacts differ from post-translational ones, indicating structural maturation.
• * Proposed a model for FtsY co-translational membrane targeting, supporting its stoichiometric role.