Biochemical and immunological characterization of the surface proteins of Borrelia burgdorferi

The immunodominant proteins and glycoproteins of Borrelia burgdorferi were analyzed by one-dimensional (1D) and 2D gel electrophoresis. More than 100 polypeptide species could be detected on silver-stained 2D gels. Separation of sonic extracts of the organism by differential centrifugation (100,000 x g) revealed several of the major proteins to reside predominantly within the pellet fraction. The antigenicity of the individual polypeptides was determined by Western (immuno-) blot analysis with sera from humans with chronic Lyme disease and from rabbits immunized with B. burgdorferi. Surface proteins of viable B. burgdorferi labeled with ¹²⁵I or long-arm hydroxysuccinimide biotin were identified by gel analysis. Thirteen major surface proteins were apparent, including the highly immunogenic 41-kilodalton (kDa) endoflagellar antigen. Two of these proteins, with molecular masses of 22 and 41 kDa, were further characterized by electroblotting and microsequencing their amino termini. Significant (35%) homology between the first 20 amino acids of the 22-kDa protein and the deduced amino acid sequence of the 31-kDa (outer surface protein A) protein of B. burgdorferi may indicate that these proteins are processed similarly or are part of a gene family expressed at the surface of the organism. In addition, highly significant (88%) homology was found between the first nine amino acids of the 41-kDa protein of B. burgdorferi and the 33-kDa endoflagellar protein of Treponema pallidum, after which the sequences diverge. This observation provides in part a structural basis for the observed cross-reactivity between the two organisms and suggests alternative approaches to the development of specific immunodiagnostics.