Biology subjects

Marintchev, A.

Publications and source records attributed to Marintchev, A..

6 recordsLinked to original sources

bioRxiv2026

NMR assignments and secondary structure analysis of the human 5MP1 C-terminal domain

Eukaryotic translation initiation is tightly regulated by interactions among translation initiation factors (eIFs) that ensure accurate start codon selection. The translation regulator, eIF5 mimic protein 1 (5MP1) contributes to this process by competing with eIF5 for binding to eIF2, thereby increasing the stringency of translation initiation. Despite its important regulatory role and emerging involvement in tumorigenesis, structural information on human 5MP1 remains limited. Here, we report the near-complete backbone and partial side-chain NMR resonance assignments of the C-terminal domain of human 5MP1 (residues 250-419), carrying a W404E substitution that disrupts dimerization. The WT protein forms a dimer at NMR concentrations, which increases the effective size of the protein and also causes disappearance of peaks corresponding to aminoacids at the dimer interface due to conformational exchange. Backbone resonance assignments were completed for 96.4% of the non-proline residues. Secondary structure was analyzed using Chemical Shift Index (CSI) and compared with the AlphaFold structural model. Regions of disagreement between the experimental and computational secondary structure assignments were further examined using 15N-NOESY-HSQC spectra, allowing experimental validation of local structural features. While the AlphaFold model accurately reproduces the overall fold of the 5MP1 C-terminal domain, several localized discrepancies were identified, particularly near the N- and C-terminal regions of the domain, where experimental NMR data support alternative secondary structure assignments. These resonance assignments and experimentally validated structural features provide a foundation for future investigations of the molecular interactions, dynamics, and functions of 5MP1 in translation initiation.

biophysics↗

bioRxiv2026

eIF4E3 drives translation of viral mRNAs with short 5' UTRs

Eukaryotic cells express three paralogs of the cap-binding protein eIF4E, yet the functions of the less-studied family members remain poorly understood. Here we demonstrate that eIF4E3, a paralog whose expression is tissue-restricted and whose activity is insensitive to inhibition by eIF4E-binding proteins (4EBPs), drives efficient translation of viral mRNAs with short 5 untranslated regions (UTRs). Many negative-strand RNA viruses (NSVs), including vesicular stomatitis virus (VSV), respiratory syncytial virus (RSV), and influenza A virus (IAV), produce mRNAs with extremely short 5UTRs that are incompatible with canonical cap-dependent scanning translation initiation. Using an auxin-inducible degron (AID) system to acutely deplete endogenous eukaryotic initiation factors during active viral infection, we demonstrate that translation of these short-UTR viral mRNAs occurs independently of eIF4E1, the canonical cap-binding protein, while remaining dependent on eIF4E3. In contrast, Ebola virus (EBOV), whose mRNAs bear long, structured 5UTRs, remains eIF4E1-dependent, implicating 5UTR length and structural complexity as cis determinants of eIF4E paralog selectivity. During VSV infection, 4EBP dephosphorylation sequesters eIF4E1 and broadly suppresses host cap-dependent translation. Because eIF4E3 escapes 4EBP-mediated regulation and preferentially engages short, unstructured 5UTRs, it is uniquely positioned to sustain viral protein synthesis under these conditions. These findings reveal that VSV exploits a cellular paralog-switching mechanism by co-opting eIF4E3 to maintain viral translation when canonical eIF4F activity is suppressed and establish eIF4E3 as a proviral factor whose tissue-restricted expression in the lung may influence susceptibility to clinically important respiratory pathogens.

molecular biology↗

bioRxiv2026

Proteolytic dissection of eIF4G reveals the closed-loop mRNP as an architecture for translation repression.

Formation of a "closed-loop" mRNP, in which the 5' cap and 3' poly(A) tail are bridged by eIF4E-eIF4G-PABP interactions, has long been proposed to drive efficient translation initiation. Direct tests of this model in mammalian cells have remained elusive. Using auxin-inducible degron (AID) technology to acutely deplete eIF4G1, we find that global translation is only partially reduced and recovers without restoration of eIF4G1 levels. We identify eIF4G3 as an underappreciated contributor to basal translation that buffers translational output upon eIF4G1 loss without increased protein expression, explaining the modest defects observed in prior RNAi-based studies. Systematic replacement of eIF4G1 with defined cleavage products and interaction mutants reveals that PABP binding by eIF4G1 is dispensable for bulk translation initiation: the central caspase-3 cleavage fragment of eIF4G1 (casp3-cpM), which lacks the PABP-interaction domain, fully rescues global protein synthesis, and acute depletion of both major cytoplasmic PABP paralogs primarily destabilizes mRNAs rather than impairing initiation. In contrast, the N-terminal enteroviral 2A cleavage product (2A-cpN) is a potent, dominant translational repressor that requires simultaneous eIF4E and PABP engagement to form a dead-end closed-loop mRNP that sequesters initiation factors without enabling 43S recruitment. These findings reveal that the eIF4G-PABP closed-loop architecture is not required for productive initiation but can be actively co-opted for translational silencing. This explains why viral eIF4G cleavage, but not factor depletion, produces near-complete translational shutoff. The modular architecture of eIF4G enables diametrically opposing translational outcomes through selective proteolytic processing.

molecular biology↗

bioRxiv2025

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 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.

biophysics↗

bioRxiv2024

Molecular basis for the interactions of eIF2β with eIF5, eIF2B, and 5MP1 and their regulation by CK2

The heterotrimeric GTPase eukaryotic translation initiation factor 2 (eIF2) delivers the initiator Met-tRNAi to the ribosomal translation preinitiation complex (PIC). eIF2{beta} has three lysine-rich repeats (K-boxes), important for binding to the GTPase-activating protein eIF5, the guanine nucleotide exchange factor eIF2B, and the regulator eIF5-mimic protein (5MP). Here, we combine X-ray crystallography with NMR to understand the molecular basis and dynamics of these interactions. The crystal structure of yeast eIF5-CTD in complex with eIF2{beta} K-box 3 reveals an extended binding site on eIF2{beta}, far beyond the K-box. We show that eIF2{beta} contains three distinct binding sites, centered on each of the K-boxes, and human eIF5, eIF2B{varepsilon}, and 5MP1 can bind to all three sites, while reducing each others affinities. Our results reveal how eIF2B speeds up the dissociation of eIF5 from eIF2-GDP to promote nucleotide exchange; and how 5MP1 can destabilize eIF5 binding to eIF2 and the PIC, to promote stringent start codon selection. All these affinities are increased by CK2 phosphomimetic mutations, highlighting the role of CK2 in both remodeling and stabilizing the translation apparatus.

biochemistry↗

bioRxiv2022

The PCI domains are "winged" HEAT domains

The HEAT domains are a family of helical hairpin repeat domains, composed of four or more hairpins. HEAT is derived from the names of four family members: huntingtin, eukaryotic translation elongation factor 3 (eEF3), protein phosphatase 2 regulatory A subunit (PP2A), and mechanistic target of rapamycin (mTOR). HEAT domain-containing proteins play roles in a wide range of cellular processes, such as protein synthesis, nuclear transport and metabolism, and cell signaling. The PCI domains are a related group of helical hairpin domains, with a "winged-helix" (WH) subdomain at their C-terminus, which is responsible for multi-subunit complex formation with other PCI domains. The name is derived from the complexes, where these domains are found: the Proteasome "lid" regulatory subcomplex, the COP9 signalosome (CSN), and eukaryotic translation initiation factor 3 (eIF3). We noted that in structure homology searches using HEAT domains, sometimes PCI domains appeared in the search results ahead of other HEAT domains, which indicated that the PCI domains could be members of the HEAT domain family, and not a related but separate group. Here, we report extensive structure homology analysis of HEAT and PCI domains, both within and between the two groups of proteins. We present evidence that the PCI domains as a group have greater structural homology with individual groups of HEAT domains than some of the HEAT domain groups have among each other. Therefore, our results indicate that the PCI domains have evolved from a HEAT domain that acquired a WH subdomain. The WH subdomain in turn mediated selfassociation into a multi-subunit complex, which eventually evolved into the common ancestor of the Proteasome lid/CSN/eIF3.

bioinformatics↗