Purification and characterization of recombinant human respiratory syncytial virus nonstructural protein NS1

We report here the first biochemical and structural characterization of the respiratory syncytial virus (RSV) NS1 protein. We have used a pET-ubiquitin expression system to produce respiratory syncytial virus (RSV) NS1 protein in E. coli that contains a hexahistidine-tag on either the amino- or carboxyl-terminus (His₆-NS1 and NS1-His₆, respectively). We have been able to isolate milligram quantities of highly purified His₆-NS1 and NS1-His₆ by nickel affinity chromatography. Generation of recombinant RSV indicated that addition of the hexahistidine tag to the C-terminus of NS1 slightly decreased viral replication competence whereas addition of the tag to the N-terminus had no observable effect. Therefore, we performed a comprehensive biochemical and biophysical characterization on His₆-NS1. His₆-NS1 is monodisperse in solution as determined by dynamic light scattering analysis. Both gel filtration and analytical ultracentrifugation showed that His₆-NS1 is predominantly a monomer. In agreement with theoretical predictions, circular dichroism spectroscopy showed that His₆-NS1 contains 21% α-helices, 34% β-sheets, and 45% undefined structure. Immunization with purified His₆-NS1 generated an antiserum that specifically recognizes NS1 by immunoprecipitation from HEp-2 cells infected by RSV, indicating that His₆-NS1 resembles native NS1. The availability of purified RSV NS1 will permit biochemical and structural investigations providing insight into the function of NS1 in viral replication and interferon antagonism.