Mx2, also known as MxB, is an interferon-stimulated gene playing a pivotal role in the innate immune response against viral infections [2,3]. It functions as a potent inhibitor of various viruses, including HIV-1, herpesviruses, and hepatitis B virus [2,3,6]. Mx2 acts at post-entry steps, for example, blocking the nuclear import of viral DNA in the case of HIV-1 [4]. It also forms cytoplasmic biomolecular condensates to trap viral capsids, preventing nuclear entry of viral genomes [1].

Human Mx2 binds to the viral capsid of HIV-1 and blocks its nuclear import [4]. Phosphorylation of Mx2 at specific serine and threonine residues regulates its antiviral activity. Some phosphorylation events enhance its activity, while others repress it, and hypermorphic mutants can inhibit HIV-1 capsid mutants resistant to wild-type Mx2 [4]. Mx2 also interacts with SAMHD1, another restriction factor, and together they restrict HIV-1 infection at post-viral DNA synthesis stage [5].

In conclusion, Mx2 is a key player in the innate immune response against viral infections. Its function in blocking nuclear entry of viral genomes and its regulation by phosphorylation are crucial aspects. The study of Mx2 using genetic models helps in understanding the complex immune defense mechanisms against viruses, especially in the context of HIV-1 infection [1,4,5].