DECORIN-BINDING PROTEIN OF BORRELIA-BURGDORFERI IS ENCODED WITHIN A 2-GENE OPERON AND IS PROTECTIVE IN THE MURINE MODEL OF LYME BORRELIOSIS

Isolated outer membranes of Borrelia burgdorferi were used in immunobl otting experiments with sera from immune mice to identify new putative Lyme disease vaccine candidates, One immunoreactive polypeptide migra ted on polyacrylamide gels just proximal to outer surface protein C an d comigrated with [H-3]palmitate-labeled polypeptides. A degenerate ol igonucleotide primer based upon internal amino acid sequence informati on was used to detect the corresponding gene within a B. burgdorferi t otal genomic library. The relevant open reading frame (ORF) encoded a polypeptide comprised of a 24-amino-acid putative signal peptide termi nated by LLISC, a probable consensus sequence for lipoprotein modifica tion, and a mature protein of 163 amino acids. Immunoblots of a recomb inant fusion protein corresponding to this ORF supported the idea that the encoded protein was a previously reported decorin-binding protein (DBP) of B. burgdorferi N40 (B. P. Guo, S. J. Norris, L. C. Rosenberg , and M. Hook Infect. Immun. 63:3467-3472, 1995). However, further DNA sequencing revealed the presence of a second ORF, designated ORF-I, w hose termination codon was 119 bp upstream of the dbp gene. ORF-1 also encoded a putative lipoprotein with a mature length of 167 amino acid s. Northern blots, Southern blots, and primer extension analyses indic ated that ORF-1 and dbp comprised a two-gene operon located on the 49- kb linear plasmid. Both proteins, which were 40% identical and 56% sim ilar, partitioned into Triton X-114 detergent extracts of B. burgdorfe ri isolated outer membranes, Mice infected with B. burgdorferi produce d high titers of antibodies against the ORF-l-encoded protein and DBP during both early and later stages of chronic infection. Both DBP and the ORF-l-encoded protein were sensitive to proteinase K treatment of intact borreliae, suggesting that they were surface exposed, In active immunization experiments, 78% of mice immunized with recombinant DBP were immune to challenge. While it is not clear whether the two lipopr oteins encoded by the ORF-1-dbp operon have analogous decorin-binding functions in vivo, the combined studies implicate DBP as a new candida te for a human Lyme disease vaccine.