Properties of repeat domain found in a novel protective antigen, SpaA, ofErysipelothrix rhusiopathiae

Abstract

Erysipelothrix rhusiopathiaeis a small gram-positive rod bacterium that causes erysipelas in swine and a variety of diseases in other animals and humans. Although live-attenuated or bacterin vaccines are effective in protecting against erysipelas, the genetic construction of their active antigen has not been identified. To clarify the surface antigen(s) involved in protective and arthritic response, using monoclonal antibody I2A against the surface proteins ofE. rhusiopathiae, we identified a protective antigen, which consists of 606 amino acids. Analysis of deletion derivatives of the gene,spaA(surface protective antigen), showd that the SpaA protein binds tightly to the bacterial cell surface via eight repeat units with a GW-module consisting of 20 amino acids at the C-terminus. Although ΔSpaA lacking their repeat units lost its ability to induce protection againstE. rhusiopathiaeinfection, intact SpaA protein showed the protection. We conclude that the presence of repeat units is essential both for the binding of SpaA to the bacterial cell surface and for protection. We believe that the repeat region at the C-terminus should be a candidate for a subunit vaccine against erysipelas.