ANTIGENIC STRUCTURE OF THE COAT PROTEIN OF POTATO MOP-TOP FUROVIRUS

The antigenic structure of the coat protein (CP) of potato mop-too fur ovirus (PMTV) was studied by electron microscopy of virus particles la beled with gold-conjugated monoclonal antibodies (MAbs) and by the rea ctions of MAbs with overlapping octapeptides (Pepscan) representing th e complete amino acid sequence of the CP. A total of seven epitopes we re identified in the CP. MAb SCR 69 detected a continuous epitope, whi ch was located at the extreme N-terminus of the CP, was exposed at the surface along the sides of PMTV particles, and was removed by treatin g them with trypsin. MAb SCR 68 detected a discontinuous epitope found at the concave end of PMTV particles. Five other epitopes, which were detected by Pepscan tests, were located internally in, and at interva ls along, the CP amino acid sequence. A tentative model of the PMTV CP subunit was produced, based on computer-aided prediction of its secon dary structure and apparent similarities with the CP of tobacco mosaic virus. In this model, four of the epitopes occur at high radius in ea ch of the pairs of parallel and anti-parallel alpha-helices in the CP subunit. The fifth is at low radius in the putative left radial alpha- helix. The epitope detected by MAb SCR 77, although amenable to study by Pepscan, contains three reactive elements, separated by short runs of nonessential residues, in a sequence of 13 amino acids. In intact v irus particles, the CPs of beet necrotic yellow vein furovirus and PMN apparently differ in the accessibility of their N- and C-termini. (C) 1994 Academic Press, inc.