Heterozygous and generalist MxA super-restrictors overcome breadth-specificity trade-offs in antiviral restriction

This study investigated how the antiviral protein MxA evolves to restrict different viruses and overcome limitations in its activity. The authors used combinatorial mutagenesis of the MxA L4 loop to generate variants and tested their ability to block H5N1 influenza and Thogoto virus (THOV). They found that some mutations created “super-restrictor” variants with much stronger antiviral activity than the normal (wild-type) MxA. However, most of these variants showed a trade-off, meaning improved restriction of one virus reduced activity against another. A key finding was that a single amino acid (position 561) largely determines this trade-off: different residues favor restriction of different viruses. Despite this limitation, rare “generalist” variants were identified that can effectively restrict both viruses. Importantly, the study showed two ways to overcome this trade-off: either evolving generalist variants or combining different specialist variants in heterozygous form, which together provide broad antiviral protection. Overall, this work reveals how host antiviral proteins adapt and suggests strategies to enhance broad-spectrum viral restriction.
(TMR)