Disease relevance of BBK32

• Fibronectin binding protein BBK32 of the Lyme disease spirochete promotes bacterial attachment to glycosaminoglycans [1].
• BBK32, a fibronectin binding MSCRAMM from Borrelia burgdorferi, contains a disordered region that undergoes a conformational change on ligand binding [2].
• BBK32 antisera protected mice from tick-borne B. burgdorferi infection and spirochete numbers were reduced by 90% within nymphs that engorged on immunized mice [3].
• In this study, we show that BBK32 shares sequence similarity with fibronectin module-binding motifs previously identified in proteins from Streptococcus pyogenes and Staphylococcus aureus [4].
• By immunoglobulin G (IgG) Western blotting (WB) or enzyme-linked immunosorbent assay (ELISA), up to 74 and 100% of acute- and convalescent-phase samples, respectively, from 23 patients with erythema migrans (EM) were positive for recombinant BBK32 protein from B. afzelii [5].

High impact information on BBK32

• BBK32 is a fibronectin-binding lipoprotein on Borrelia burgdorferi, the causative agent of Lyme disease [2].
• Therefore, B. burgdorferi bbk32 and bbk50 expression within Ixodes scapularis ticks and the murine host, and the effect of BBK32 and BBK50 antisera on spirochetes throughout the vector-host life cycle were investigated. bbk32 and bbk50 mRNA and protein were first detected within engorged ticks, demonstrating regulated expression within the vector [3].
• These data demonstrate that bbk32 and bbk50 are expressed during tick engorgement and that BBK32 antisera can interfere with spirochete transmission at various stages of the vector-host life cycle [3].
• The resulting mutant does not synthesize BBK32, exhibits reduced fibronectin binding in solid phase assays and manifests decreased interactions with mouse fibroblast cells relative to both the infectious parent and genetic complement [6].
• Recombinant BBK32 recognized purified heparin, indicating that the bacterial attachment to GAGs was due to direct binding by BBK32 [1].

Biological context of BBK32

• In this study, we show that, when BBK32 was produced from a shuttle vector in an otherwise nonadherent high-passage B. burgdorferi strain, the protein localized on the bacterial surface and conferred attachment to fibronectin and to mammalian cell monolayers [1].
• Our data indicated that B. burgdorferi lacking BBK32 retained full pathogenicity in mice, regardless of whether mice were infected artificially by syringe inoculation or naturally by tick bite [7].
• In the serology of disseminated LB, the three variant BBK32 antigens cross-reacted [5].
• The identities between the amino acid sequences of the BBK32 proteins from Borrelia burgdorferi sensu stricto, B. garinii, and B. afzelii isolates were 71 to 100% [5].

Anatomical context of BBK32

• Three recombinant antigens, decorin binding protein A (DbpA), BBK32, and outer surface protein C (OspC), and IR(6) peptide of borrelial VlsE protein, were evaluated for the diagnosis of neuroborreliosis (NB), using cerebrospinal fluid (CSF) and serum samples from 89 patients [8].
• In IgG ELISA at presentation of EM, 65/75 (87 %) patients had antibodies to one or more variants of BBK32, 29/75 (39 %) had antibodies to flagella and 29/75 (39 %) had antibodies to the VlsE IR(6) peptide antigen [9].

Associations of BBK32 with chemical compounds

• In addition, the high-passage strain producing BBK32 bound to purified preparations of the GAGs dermatan sulfate and heparin, as well as to these GAGs on the surfaces of cultured mammalian cells [1].
• To test this hypothesis, we constructed an isogenic BBK32 deletion mutant from wild-type B. burgdorferi B31 by replacing the BBK32 gene with a kanamycin resistance cassette through homologous recombination [7].

Analytical, diagnostic and therapeutic context of BBK32

• Analysis of changes in circular dichroism spectra of the N-terminal segment of BBK32 upon binding of the N-terminal domain of fibronectin revealed an increase in beta-sheet content in the complex [2].
• Analysis of purified recombinant forms of the two domains by circular dichroism spectroscopy, gel permeation chromatography, and intrinsic viscosity determination were consistent with an N-terminal-extended, unstructured segment and a C-terminal globular domain in BBK32 [2].
• The performance of ELISAs with the recombinant antigens decorin-binding protein A (DbpA), DbpB, and BBK32 (from Borrelia afzelii, B. garinii, and B. burgdorferi sensu stricto) and VlsE peptide antigen invariable region 6 (IR(6)) were evaluated in the serodiagnosis and follow-up of children with Lyme arthritis (LA) [10].
• The specificities of the IgG ELISA with the variant BBK32 antigens for EM and disseminated borreliosis were 81 to 92% and 89 to 95%, respectively [5].
• Our findings indicate that the BBK32 proteins are promising serodiagnostic antigens for the detection of early and disseminated LB but that variant BBK32 proteins may be needed either in parallel or in combination with an immunoassay for LB to cover all the relevant borrelial species that cause the disease [5].

References