Unexpected Electrophoretic Behavior of Complexes between Rod-like Virions and Bivalent Antibodies

Here we report on the unexpected electrophoretic behavior of complexes between rod-like virus particles (virions) and bivalent antibodies. The multiple complexes formed by the virions and antibodies migrated with electrophoretic mobilities of much greater absolute values than those of the unbound virions or antibodies while typically complexes have mobilities intermediate to those of their components. We hypothesized that the mobilities of unusually high absolute values are caused by the cross-linking of virions by bivalent antibodies into aggregates with prominent side-to-side binding. Theoretically, the mobility of such aggregates should be proportional to the square root of the number of cross-linked virions. The formation of virion aggregates with prominent side-to-side binding was confirmed by atomic force microscopy. The dependence of the aggregate mobility on the number of cross-linked virions can be used to estimate this number.