A MYRISTYLATED MEMBRANE-PROTEIN ENCODED BY THE VACCINIA VIRUS L1R OPEN READING FRAME IS THE TARGET OF POTENT NEUTRALIZING MONOCLONAL-ANTIBODIES

We identified a protein component of the intracellular mature vaccinia virion membrane that is a target of a potent neutralizing monoclonal antibody, 7D11, obtained from Alan L. schmaljohn. By immunofluorescent and electron microscopic analysis, MAb 7D11 was found to stain intrac ytoplasmic viral factories, virion membranes in cell sections, and the surface of negatively stained preparations of purified virions. The M Ab 7D11 antigen, which is synthesized at late times in infection, has apparent molecular masses of 25 and 29 kDa under nonreducing and reduc ing conditions, respectively. The membrane antigen was most efficientl y extracted from virions by NP40 detergent in combination with a reduc ing agent; in addition, the protein partitioned exclusively into the d etergent phase when extracted with Triton X-114. Although the N-termin us of the immunoaffinity-purified protein was blocked, sequence analys is of trypic peptides revealed that the MAb 7D11 antigen was identical to the myristylated protein encoded by the L1R open reading frame pre viously described by C. A. Franke, E. M. Wilson, and D. E. Hruby (1990 , J. Virol. 64, 5988-5996). Validation of this genetic assignment was provided by the ability of MAb 7D11 to immunoprecipitate a [H-3]myrist ic acid-labeled product of the expected molecular weight from infected cells. In addition, we discovered that the previously described neutr alizing monoclonal antibody 205 (Y. Ichihashi, T. Takahashi, and M. Oi e, 1994, Virology 202, 834-843) also recognizes the L1R protein. (C) 1 995 Academic Press, Inc.