Purification and Characterization of a Human Mx Protein

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Abstract
Human interferon-.beta. (IFN-.beta.) induces in human embryonic foreskin fibroblasts a cytoplasmic protein with antigenic similarities to mouse Mx protein, a nuclear protein implicated in inhibition of influenza virus replication. The human protein was purified to virtual homogeneity by immunoaffinity chromatography using a monoclonal antibody to mouse Mx protein. The purified protein has an apparent Mr of 78,000 and displays a strong tendency to self-aggregate. It can be resolved on two-dimensional gels into four spots with pIs between 6.0 and 6.2, each of which reacts with antibodies to mouse Mx protein. The partial animo-terminal sequence was determined for the affinity-purified protein. Cytoplasmic microinjection of the affinity-purified protein does not lead to efficient protection against infection with influenza virus. Cytoplasmic microinjection of the monoclonal Mx antibody, which increases susceptibility of IFN-treated mouse Mx cells to influenza virus, does not alter the viral susceptibility of IFN-treated human cells. These results suggest that, unlike the mouse Mx protein, the human Mx protein studied in this communication may not be sufficient to confer to cells high degree of protection against influenza virus.