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

Abstract

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 1H-15N HSQC spectrum is consistent with an intrinsically disordered protein region. Several amide resonances were broadened at 25 {degrees}C but recovered at 5 {degrees}C. Secondary structure propensities derived from chemical shift index (CSI) analysis, together with amide 1H chemical shift temperature coefficients (CSTCs), confirm that the protein is disordered, while the CSI analysis also indicates the presence of short segments with modest -helical or {beta}-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.