MX1

Mx1 is a gene in mammals that encodes a member of the myxovirus resistance (Mx) protein family, known as Mx1. The protein is an interferon-induced, large GTPase and belongs to the dynamin superfamily. Expression is upregulated by type I and III interferons in response to viral infection, and the protein is primarily located in the cytoplasm where it can form oligomers.

The antiviral activity of Mx1 proteins is broad in cell culture and in vivo, with notable potency against several RNA viruses, especially orthomyxoviruses such as influenza A. The exact antiviral mechanism is not fully understood, but is thought to involve interference with viral ribonucleoprotein complexes, blocking viral transcription and replication or otherwise impeding genome dissemination within the cell. The efficiency of restriction can vary by virus strain and cellular context.

Species context and genetic variation are important. In mice, a functional Mx1 allele confers strong resistance to influenza A; many laboratory strains carry mutations that compromise function. In humans, the MX1 gene encodes the MxA protein, which also exhibits antiviral activity in vitro, though its protective role against influenza in humans is less clearly defined and appears influenced by genetic background. Several common single-nucleotide polymorphisms in MX1 can affect expression levels and antiviral potency.

Clinical and research relevance centers on Mx1/MxA as a marker of interferon response and a subject of study in antiviral defense. Mx proteins have been explored for their potential to inform antiviral strategies and to illuminate host factors that influence susceptibility to viral infections. Some viruses may evolve mechanisms to partially counteract Mx1/MxA-mediated restriction.