Molecular analysis of the outer surface protein A (OspA) of Borrelia burgdorferi for conserved and variable antibody binding domains

The outer surface protein A (OspA) of Borrelia burgdorferi is a major candidate for development of a borrelia vaccine. However, vaccine development may be aggravated by the immunological heterogeneity of OspA. In this respect the knowledge about conserved and variable epitopes is of major interest. In this study truncated proteins derived from two different OspA serotypes of B. burgdorferi were mapped for conserved and specific antibody-binding domains. The OspA fragments were reacted in the Western blot with eight different Osp Aspecific monoclonal antibodies recognizing between one and seven of the seven OspA serotypes previously described. The two broadly reacting antibodies (recognizing all serotypes) react with N-terminal fragments of 93 and 214 amino acids, respectively, whereas antibodies recognizing only one and two to four of the seven serotypes are reactive with C-terminal fragments of amino acid 143-273 and 109-273, respectively. Thus, conserved antibody-binding domains are located nearer to the N terminus than serotype-specific ones. Comparison of the results from western blot mapping with OspA sequence data suggested certain conserved or variable regions as probable candidates for antigenic sites involved in linear or conformationally dependent epitopes. This, however, needs to be confirmed by epitope mapping using the respective synthetic peptides.