NMR assignments and secondary structure analysis of the eIF1-interacting fragment of human eIF3c

Eukaryotic translation initiation involves coordinated assembly of initiation factors on the small ribosomal subunit to form the pre -initiation complex (PIC) and scan mRNA for the start codon. The multi-subunit initiation factor eIF3 plays central roles in PIC assembly, stabilization, and scanning. Within eIF3c, residues 166–266 lie immediately N-terminal of the folded PINT/PCI domain and encompass the reported eIF1-binding site in human eIF3c. This segment is not visible in PIC Cryo-EM structures, except for a small helix contacting eIF1, and is predicted to be intrinsically disordered. Here we report the near-complete backbone and partial side-chain NMR assignments for the eIF3c 166–266 fragment in solution. The ¹ H– ¹⁵ N HSQC spectrum is consistent with an intrinsically disordered protein region. Several amide resonances were broadened at 25 °C but recovered at 5 °C. Secondary structure propensities derived from chemical shift index (CSI) analysis, together with amide ¹ H chemical shift temperature coefficients (CSTCs), confirm that the protein is disordered, while the CSI analysis also indicates the presence of short segments with modest α-helical or β-strand propensity. Three conserved FLKK motifs fall at junctions of these transient structural elements, with Motif 3 located in the subsegment showing slightly greater propensity for transient structure. These residue-specific NMR assignments provide a foundation for future studies of interaction surfaces, binding-induced folding, and conformational dynamics of this conserved eIF3c region in the context of translation initiation.