Structure Analysis Of The Stalk Domain Of MxB,A Host Innate Inhibitor Of HIV-1

Interferon(IFN)is a key component of the innate immune response to exogenous pathogens.Interferon increases the mRN A levels of interferon-stimulated genes(ISGs)in vivo,which is thought to account for its antiviral activity.Recent studies have indicated that human myxovirus resistance protein 2(Mx2 or MxB),one of these ISGs,contributes to the inhibition of HIV-1 replication by interferon.MxB may bind to HIV-1 relatively late in the post-entry phase,and it leads to a reduced level of integrated viral DNA,thereby restricting HIV-1 infection.The N-terminal 91-aa domain of MxB and the assembly of MxB mediated by the Stalk domain have also been shown to be indispensible for MxB’s anti-viral functions,but the mechanism involved has remained elusive.We have generated and screened a series of deletion constructs of human MxB with an N-terminal His-Sumo-tag,but only Δ1-83,Stalk(417-680),GF,N-GF show high solubility and stability.After removing His-Sumo-tags,all of them are mainly eluted in the aggregation fraction in Gel-filtration only except GF.After a series of mutations,we finally got the ideal crystal of human MxB Stalk and solved the structrue(2.9 ?).MxB Stalk shows one dimer in the asymmetric unit.Each monomer contains a four-helix bundle.analyses of MxB dimer interfaces show that the majority of residues involved in the interface are not conserved between MxB and MxA,contributing to the building of a more stable MxB dimer.The Stalk domain of MxA and MxB Stalk domain share 46.7% sequence identity,and the structure of the MxA Stalk domain and the overall structure of Mx B Stalk have a similar conformation.Our results indicate that although human Mx proteins share common structural characteristics,their dimerization strategies are unique,contributing to their unique contributions to viral restriction.Our crystal structure provides a more detailed picture of the dimer interface of the MxB Stalk domain,which may facilitate further studies of the functional details of MxB’s anti-HIV activity.The study of the structure of MxB will make us understand better of the mechanism of HIV-1 virus,the details of which may be helpful for the study of efficient anti-viral drugs.