Characterization of surface antigen from Lyme disease spirochete Borrelia burgdorferi

Borrelia burgdorferi, the Lyme disease spirochete, possesses a surface protein, VIsE (variable major protein-like sequence, expressed), that undergoes antigenic variation. Unlike conserved regions of other proteins involved in antigenic variation, the most conserved invariable region of VIsE is immunodominant in Lyme-disease patients. Physicochemical analyses of pure recombinant VIsE yielded the following results: The protein appeared oligomeric in solution, with a secondary structure dominated by a-helices. Thermal denaturation (pH 7) probed by calorimetry involved two transitions: oligomer-to-monomer conversion (around 40 degreesC) followed by protein unfolding (55 +/- 1 degreesC). Chemical denaturation monitored by far-UV circular dichroism (20 degreesC, pH 7) sensed only polypeptide unfolding and took place in a single transition (DeltaG(U)(H2O) = 23 +/- 2 kJ/mol). VIsE did not adopt a native structure at pH 3; at pH 10 the stability was significantly reduced. Knowledge of biophysical properties of VIsE may aid in understanding the mechanism of VIsE antigenic variation in B. burgdorferi. (C) 2001 Elsevier Science