Localization of BmpA on the Exposed Outer Membrane ofBorrelia burgdorferiby Monospecific Anti-Recombinant BmpA Rabbit Antibodies

Abstract

BmpA (P39) is an immunodominant chromosomally encodedBorrelia burgdorferiprotein. The potential strong cross-reactivity of anti-BmpA antibodies with the other members of this paralogous protein family and the previous use of antibodies whose reactivity to the other Bmp proteins was uncharacterized have resulted in continued controversy over its localization inB. burgdorferi. In an effort to provide a definitive demonstration of the localization of BmpA, rabbit antibodies raised to recombinant BmpA (rBmpA) were rendered monospecific by absorption with rBmpB. This reagent did not react with rBmpB, rBmpC, or rBmpD in dot immunobinding, detected only a single 39-kDa band and a single 39-kDa, pI 5.0 spot on one- and two-dimensional immunoblots ofB. burgdorferilysates, respectively, and immunoprecipitated a single 39-kDa protein from these lysates. It detected BmpA in the Triton X-114-soluble and -insoluble fractions ofB. burgdorferi, suggesting association with both inner and outer bacterial cell membranes. Treatment of intactB. burgdorferiwith proteinase K partially digested BmpA, consistent with a limited surface exposure on the outer bacterial membrane, a suggestion confirmed by immunofluorescence of unfixedB. burgdorfericultured in vitro and in vivo. Anti-rBmpA antibody was bacteriostatic forB. burgdorferiB31 in culture, again suggesting localization of BmpA on the exposed spirochetal outer surface. Surface localization of BmpA, growth inhibition by anti-rBmpA antibodies, and the previously reported conservation ofbmpAin differentB. burgdorferisensu lato strains may indicate that BmpA plays an essential role inB. burgdorferibiology.