Topographical analysis of the G virion of Aleutian mink disease parvovirus with monoclonal antibodies

The topography of the Aleutian mink disease parvovirus (ADV) G virion was analyzed with monoclonal antibodies and polyclonal antiserum. There was homology between the two major structural proteins as others have previously reported. Trypsin treatment of the virion with subsequent immunoblotting revealed that VP2 represents the main peptide on the exterior of virion and that VP1 is probably embedded within the capsid. Additional analyses of the trypsin-treated virions showed that VP2 is responsible for binding complement and that it also represents the structural part of the virion that binds to cellular receptors. A third protein, p34, was detected that might represent a third structural polypeptide because of its many unique epitopes relative to the other peptides detected.

Capsid protein VP1 (p85) of Aleutian disease virus is a major DNA-binding protein

The interaction between Aleutian disease virus (ADV) DNA and proteins isolated from ADV-infected cells or ADV virions, respectively, was examined. Proteins were separated on SDS-polyacrylamide gels, transferred to nitrocellulose, and probed with 32P-labeled restriction fragments of replicative form (RF) DNA or with single-stranded virion DNA. The ADV capsid protein VP1 was found to bind the 3'-terminal BamHI fragment of RF DNA extending from map units (m.u.) 0 to 15. No binding was observed with the fragment extending from m.u. 15 to 63 and only minor amounts of label were detected with the 5'-terminal EcoRV fragment extending from m.u. 63 to 100. With the latter fragment, small amounts of label were also detected bound to higher-molecular-weight proteins of about 100,000 Da. No binding of DNA to the ADV nonstructural protein NS1 or to the ADV capsid protein VP2 was detected. Additionally, single-stranded virion DNA was found to bind to VP1.

Apparent lack of neutralizing antibodies in Aleutian disease is due to masking of antigenic sites by phospholipids

It is generally accepted that Aleutian disease virus (ADV) cannot be neutralized by antibodies either in vivo or in vitro. We found several ways to demonstrate neutralization of ADV by specific antibodies from mink. It was essential to make ADV monodisperse by treatment with sodium lauroyl sarkosyl or n-butanol or by filtration through 0.05-micron membranes before neutralization tests. In kinetic experiments, there was a 95% loss of virus infectivity within the first 5 min of reaction, but a resistant fraction of about 1% remained after 1.5 hr of incubation. Neutralization titers between 1:160 and 1:640 were found in sera from naturally and experimentally infected mink. A positive relation was consistently found between neutralization and ELISA titers. Furthermore, separation of phospholipids from ADV was shown by thin-layer chromatography of butanol-extracted virions. By reconstitution of monodispersed ADV with various lipids, phospholipids were found to interfere with virus neutralization by attachment to the virus surface.