Research background
Matrix protein 1 (M1) is the most abundant structural protein of influenza A virus and coordinates several steps of the replication cycle, including nuclear export of viral ribonucleoprotein (vRNP) complexes, virion assembly and budding. Because M1 must reach the cytoplasm after a nuclear phase, the signals that govern its trafficking have been of long-standing interest to virologists.
Cao and colleagues mapped a hydrophobic nuclear export signal to M1 residues I59 through V68, the decamer ILGFVFTLTV, and identified I59, V63, L66 and V68 as the positions that matter most for activity. Using EGFP fusion constructs and fluorescence localization in transfected and infected cells, they showed that this segment is sufficient to redirect a reporter protein out of the nucleus. Export driven by the segment was not sensitive to leptomycin B, distinguishing it from the classical CRM1-dependent route followed by the control NEP-12-21 signal. A combined L66A/V68A substitution impaired both M1 and vRNP export and reduced virus titers by roughly 300-fold, establishing the signal as important for efficient replication rather than merely dispensable.
What makes this region unusual is that it does double duty. Terajima and Ennis noted in a subsequent exchange in the same journal that the export signal overlaps almost entirely with M1 58-66, GILGFVFTL, the immunodominant HLA-A*02:01-restricted CD8+ T-cell epitope of influenza A. They argued that this superposition helps explain a puzzle in influenza immunology: although HLA-A2 is carried by a large fraction of the human population, escape variants within this epitope are scarce in circulating strains, plausibly because substitutions that abolish T-cell recognition would simultaneously compromise a signal the virus needs. The original authors replied in the same correspondence. Later work has examined how selective pressure from M1 58-66-specific CD8+ T cells is instead accommodated by substitutions outside the epitope itself, and separate studies have reported that recognition of this epitope is not strictly limited to HLA-A*02:01.
LT9744 supplies the 59-68 decamer as a sequence-defined reagent spanning both the export-signal and epitope registers. Note that it is offset from the 58-66 nonamer by one residue at each end; the two peptides are not interchangeable in binding or T-cell assays, and results obtained with one register should not be assumed to transfer to the other.
Research applications
- Nuclear export assays using reporter fusions, as a wild-type reference against L66A/V68A and other alanine-substituted variants
- Testing CRM1 dependence of export activity with leptomycin B alongside classical CRM1-dependent control signals
- HLA-A*02:01 peptide binding and complex stabilization assays, including T2 cell surface stabilization
- Refolding of peptide-HLA monomers and assembly of tetramers or other multimers for antigen-specific CD8+ T-cell detection
- IFN-gamma ELISpot and intracellular cytokine staining with human PBMC from influenza-exposed or vaccinated donors
- Register and length-variant comparisons against the M1 58-66 nonamer GILGFVFTL
- Mapping the relationship between viral protein function and epitope conservation in sequence-evolution studies
References
- Cao S, Liu X, Yu M, et al. A nuclear export signal in the matrix protein of influenza A virus is required for efficient virus replication. Journal of Virology (2012) 86:4883-4891. doi:10.1128/JVI.06586-11
- Terajima M, Ennis FA. Nuclear export signal and immunodominant CD8+ T cell epitope in influenza A virus matrix protein 1. Journal of Virology (2012). doi:10.1128/JVI.00894-12
- Reply to “Nuclear export signal and immunodominant CD8+ T cell epitope in influenza A virus matrix protein 1”. Journal of Virology (2012). doi:10.1128/JVI.01245-12
- The immunodominant influenza A virus M1 58-66 cytotoxic T lymphocyte epitope exhibits degenerate class I major histocompatibility complex restriction in humans. Journal of Virology (2014) 88:10613. doi:10.1128/JVI.00855-14
- Selective pressure mediated by influenza virus M1 58-66 epitope-specific CD8+ T cells promotes accumulation of extra-epitopic amino acid substitutions associated with viral resistance to these T cells. Virus Research (2024). PMC10955411
Related MHC class I epitope peptides
For research use only. Not for use in diagnostic or therapeutic procedures, or for human or veterinary use.
