VraA (BBI16) protein of Borrelia burgdorferi is a surface-exposed antigen with a repetitive motif that confers partial protection against experimental Lyme borreliosis

We have previously described the expression cloning of nine Borrelia burgdo rferi antigens, using rabbit serum enriched for antibodies specific for inf ection-associated antigens, and determined that seven of these antigens wer e associated with infectious B. burgdorferi strain B31, One of these infect ion-associated antigens encoded a 451-amino-acid putative lipoprotein conta ining 21 consecutive and invariant 9-amino-acid repeat sequences near the a mino terminus that we have designated VraA for virulent strain-associated r epetitive antigen A. The vraA locus (designated BBI16 by The Institute for Genomic Research) maps to one of the 28-kb linear plasmids designated 1p28- 43 that is not present in noninfectious strain B31 isolates. Subsequent PCR analysis of clonal isolates of B. burgdorferi B31 from infected mouse skin revealed a clone that lacked only 1p28-4, Southern blot and Western blot a nalyses indicated that the 1p28-4 and VraA proteins, respectively, were mis sing from this clone, We have also determined that VraA is a surface-expose d protein based on protease accessibility assays of intact whole cells. Fur thermore, vraA expression is modestly derepressed when cells are grown at 3 7 degreesC relative to cells grown at 32 degreesC, suggesting that VraA is, in part, a temperature-inducible antigen. Homologues cross-reactive to B. burgdorferi B31 VraA, most with different molecular masses, were identified in several B. burgdorferi sensu late isolates, including B, andersonii, su ggesting that the immunogenic epitope(s) present in strain B31 VraA is cons erved between Borrelia spp. In protection studies, only 8.3% of mice (1 of 12) immunized with full-length recombinant VraA fused to glutathione S-tran sferase (GST) were susceptible to infectious challenge with 10(2) B. burgdo rferi strain B31, whereas naive mice or mice immunized with GST alone were infected 40% or 63 to 67% (depending on tissues assayed) of the time, respe ctively, As such, the partial protection elicited by VraA immunization prov ides an additional testable vaccine candidate to help protect against Lyme borreliosis.