Early Scanning of Nascent Polypeptides inside the Ribosomal Tunnel by NAC

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Protein maturation begins during synthesis, a process fundamental for cellular function.
• Protein biogenesis factors typically interact with polypeptides after they emerge from the ribosome.
• The precise timing and location of these interactions are critical for protein homeostasis.

Purpose of the Study:

• To identify the mechanism by which protein biogenesis factors recognize nascent polypeptides.
• To investigate the role of the nascent polypeptide-associated complex (NAC) in early protein synthesis.
• To elucidate the in vivo significance of NAC’s interaction with nascent chains within the ribosomal tunnel.

Main Methods:

• In vivo studies using Caenorhabditis elegans as a model organism.
• Analysis of nascent chain recognition by the nascent polypeptide-associated complex (NAC).
• Investigation of NAC's interaction with ribosomal components and its role in protein transport.

Main Results:

• The N-terminal tail of NAC’s β subunit (N-βNAC) directly probes the ribosomal tunnel.
• NAC senses nascent polypeptides near the peptidyl-transferase center, escorting them to the cytosol.
• NAC’s tunnel-probing activity is essential for C. elegans viability and regulates ER protein transport by influencing ribosome-Sec61 interactions.

Conclusions:

• Eukaryotic protein maturation involves early sampling of nascent chains inside the ribosomal tunnel by NAC.
• This mechanism is vital for organismal survival and proper protein biogenesis.
• NAC plays a critical role in coordinating protein synthesis with downstream processing pathways like ER translocation.