Structure of a human cap-dependent 48S translation pre-initiation complex.

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Eukaryotic translation initiation is a complex, regulated process essential for protein synthesis.
• Key initiation factors (eIFs), including the eIF4F complex and eIF4B, are crucial for mRNA recruitment and ribosome loading.
• The 48S pre-initiation complex forms on the mRNA and scans for the start codon.

Purpose of the Study:

• To structurally characterize the human 48S pre-initiation complex after start codon recognition.
• To map the protein-protein interaction network within the assembled h-48S complex.
• To provide a high-resolution molecular snapshot of translation initiation.

Main Methods:

• Reconstitution of human 48S complexes using purified components.
• Cross-linking/mass spectrometry to identify protein interactions.
• Cryo-electron microscopy (cryo-EM) to determine the complex structure at 6.3 Å resolution.

Main Results:

• The cryo-EM structure reveals the arrangement of initiation factors and the ribosome in the h-48S complex.
• Most eIF4B and eIF4F factors show flexibility, but eIF4B's RNA-recognition motif is localized at the 40S mRNA channel entrance.
• Core and additional eIF3 subunits bind to the 40S subunit's solvent-exposed side, while eIF2 and initiator-tRNA are positioned at the intersubunit side, bound to the start codon.

Conclusions:

• The study provides a detailed structural view of the human 48S complex post-start codon recognition.
• Identifies specific localization and potential roles of key initiation factors, including eIF4B and eIF3 subunits.
• Advances understanding of the molecular mechanisms governing the critical step of translation initiation in eukaryotes.