Crosslinking of and Coupling to Viral Capsid Proteins by Tyrosine Oxidation Original Research Article

Cowpea mosaic virus is composed of 60 identical copies of a two-subunit protein organized in pentameric assemblies around the icosahedral 5-fold symmetry axis. Treatment of the virus with the Ni(II) complex of the tripeptide GGH and a peroxide oxidant, or irradiation in the presence of Ru(bpy)32+ and persulfate generates covalent crosslinks across the pentameric subunit boundaries, effectively stitching the subunits together. Intersubunit crosslinking was found to occur exclusively at adjacent tyrosine residues (Y52-Y103), as predicted from the X-ray crystal structure of the capsid, and to be more extensive with the photochemical ruthenium system. The Ni/GGH oxidative procedure was also used to make covalent attachments to the virion by trapping with a functionalized disulfide reagent.