Summary auto-generated
This study investigates how the influenza A (H1N1) virus membrane (M) protein correlates with hemagglutinin (HA) receptor-binding specificity. Researchers created reassortant viruses between A/Aichi/4/92 and A/WSN/33 strains, differing only in the M gene source. Viruses with the A/Aichi/4/92-derived M protein (PW13, PW15) agglutinated chicken red blood cells (CRBC), while those with WSN-derived M protein (PW10, PW70) did not, despite having identical HA genes. The HA proteins themselves lacked CRBC-binding ability when expressed alone, indicating modification occurred during infection. Co-expression experiments revealed that neuraminidase (NA) activity, rather than direct M protein interaction, modified HA to gain CRBC-binding capacity. Treatment with exogenous neuraminidase restored CRBC binding in non-responder viruses. The M1 protein showed differential intracellular localization timing: in PW15-infected cells, M1 migrated from nucleus to cytoplasm coinciding with CRBC adsorption; in PW10-infected cells, M1 remained nuclear throughout infection. These findings suggest the M protein facilitates NA-mediated desialylation of HA sugar chains at the cell surface, enabling altered receptor specificity.
Key findings
- Reassortant influenza viruses differing only in M protein source showed contrasting phenotypes: A/Aichi/4/92-derived M enabled CRBC agglutination while WSN-derived M prevented it, despite identical HA genes
- HA protein modification required neuraminidase enzymatic activity rather than direct M protein-HA interaction, as external NA treatment restored CRBC-binding capacity
- M1 protein intracellular trafficking correlated with phenotype: timely migration from nucleus to cytoplasm (PW15) enabled HA modification and CRBC binding, while retention in nucleus (PW10) prevented modification
- M protein likely facilitates organized packing or arrangement of HA and NA proteins at the plasma membrane, enabling NA to remove sialic acid modifications that mask CRBC-binding sites on HA
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Abstract
From the reassortment experiments between A/Aichi/4/92 and A/WSN/33 (WSN) (H1N1) viruses, two different phenotype viruses which contained the haemagglutinin (HA) gene from A/Aichi/4/92 virus and the neuraminidase (NA) gene from WSN virus were obtained. PW13 and PW15 viruses agglutinated chicken red blood cells (CRBC), while PW10 and PW70 viruses did not. However, the expressed HA proteins of these viruses did not adsorb CRBC. The difference in gene constellation between PW13, PW15 and PW10, PW70 viruses was the membrane protein (M) gene. The former two had the M gene from A/Aichi/4/92 virus and the latter two had that from WSN virus. In PW15-infected cells, haemadsorption of CRBC was observed 30 min later than that of goose red blood cells and the M1 protein migrated from the nucleus to the cytoplasm 30 min earlier than adsorption of CRBC was observed. On the other hand, in PW10-infected cells, haemadsorption of CRBC was not observed through the virus replication and the M1 protein stayed in the nucleus after HA and NA activities reached maximum levels. Co- expression of the M and the HA proteins of A/Aichi/4/92 virus did not help the HA protein gain the ability to adsorb CRBC. However, neuraminidase treatment of COS cells expressing the HA protein of A/Aichi/4/92 virus or MDCK cells infected by PW10 virus restored the ability to adsorb CRBC. We discussed the possibility that the M1 protein helped the NA protein in its role to modify the HA protein on the cell surface.