Evidence that the mature form of the flavivirus nonstructural protein NS1 is a dimer

Evidence is presented which indicates that the dengue-2 virus nonstructural protein NS1 (soluble complement fixing antigen) exists in infected BHK and mosquito cell cultures as part of a stable oligomer. Identification of the dissociation products of the isolated oligomer and comparison of the number of N-linked glycans in native and denatured NS1 is consistent with the idea that the high-molecular-weight form of NS1 is a homodimer. By analyzing lysates of BHK cells infected with St. Louis encephalitis virus or Powassan virus and proteins from dengue-2 virus-infected mouse brain we have demonstrated that the appearance of the high-molecular-weight form of NS1 is a general feature of flavivirus infection. It is formed between 20 and 40 min after NS1 is synthesized and before the protein passes the Golgi apparatus. Both soluble and pelletable extracellular NS1 are also found as the high-molecular-weight form.