Decorin Binding Protein Research Articles

Decorin-binding protein of Borrelia burgdorferi is encoded within a two-gene operon and is protective in the murine model of Lyme borreliosis.

Isolated outer membranes of Borrelia burgdorferi were used in immunoblotting experiments with sera from immune mice to identify new putative Lyme disease vaccine candidates. One immunoreactive polypeptide migrated on polyacrylamide gels just proximal to outer surface protein C and comigrated with [3H]palmitate-labeled polypeptides. A degenerate oligonucleotide primer based upon internal amino acid sequence information was used to detect the corresponding gene within a B. burgdorferi total genomic library. The relevant open reading frame (ORF) encoded a polypeptide comprised of a 24-amino-acid putative signal peptide terminated by LLISC, a probable consensus sequence for lipoprotein modification, and a mature protein of 163 amino acids. Immunoblots of a recombinant 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. Höök, Infect. Immun. 63:3467-3472, 1995). However, further DNA sequencing revealed the presence of a second ORF, designated ORF-1, whose termination codon was 119 bp upstream of the dbp gene. ORF-1 also encoded a putative lipoprotein with a mature length of 167 amino acids. Northern blots, Southern blots, and primer extension analyses indicated 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% similar, partitioned into Triton X-114 detergent extracts of B. burgdorferi isolated outer membranes. Mice infected with B. burgdorferi produced high titers of antibodies against the ORF-1-encoded protein and DBP during both early and later stages of chronic infection. Both DBP and the ORF-1-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 lipoproteins encoded by the ORF-1-dbp operon have analogous decorin-binding functions in vivo, the combined studies implicate DBP as a new candidate for a human Lyme disease vaccine.

Active and passive immunity against Borrelia burgdorferi decorin binding protein A (DbpA) protects against infection.

Borrelia burgdorferi, the spirochete that causes Lyme disease, binds decorin, a collagen-associated extracellular matrix proteoglycan found in the skin (the site of entry for the spirochete) and in many other tissues. Two borrelial adhesins that recognize this proteoglycan, decorin binding proteins A and B (DbpA and DbpB, respectively), have recently been identified. Infection of mice by low-dose B. burgdorferi challenge elicited antibodies against DbpA and DbpB that were sustained at high levels, suggesting that these antigens are expressed in vivo. Scanning immunoelectron microscopy showed that DbpA was surface accessible on intact borreliae. Passive administration of DbpA antiserum protected mice from infection following challenge with heterologous B. burgdorferi sensu stricto isolates, even when serum administration was delayed for up to 4 days after challenge. DbpA is the first antigen target identified that is capable of mediating immune resolution of early, localized B. burgdorferi infections. DbpA immunization also protected mice from B. burgdorferi challenge; DbpB immunization was much less effective. DbpA antiserum inhibited in vitro growth of many B. burgdorferi sensu lato isolates of diverse geographic, phylogenetic, and clinical origins. In combination, these findings support a role for DbpA in the immunoprophylaxis of Lyme disease and suggest that DbpA vaccines have the potential to eliminate early-stage B. burgdorferi infections.

Adherence of Borrelia burgdorferi to the proteoglycan decorin.

Lyme disease is a tick-borne infection that can develop into a chronic, multisystemic disorder. The causative agent, Borrelia burgdorferi, is initially deposited by the tick into the host dermis, where it associates with collagen fibers, replicates, and eventually disseminates to other tissues. We have examined the adherence of the spirochete to different components of the collagen fiber and demonstrated that decorin, a proteoglycan which decorates collagen fibers, can support the attachment of B. burgdorferi. No significant direct attachment to isolated type I or III collagens could be detected. Attachment of the spirochetes to decorin was highly specific, and the process could be inhibited by soluble decorin but not by various unlabeled, unrelated components. B. burgdorferi also bound soluble 125I-labeled decorin in a time- and concentration-dependent manner. Spirochete binding of soluble 125I-labeled decorin required intact proteoglycan and could not be inhibited by either isolated core protein or glycosaminoglycan chain. B. burgdorferi expresses two decorin-binding proteins with apparent molecular masses of 19 and 20 kDa as revealed in a Western blot (immunoblot)-type assay. Our results indicate that decorin may mediate the adherence of B. burgdorferi to collagen fibers in skin and other tissues.