Further characterization of complement regulator-acquiring surface proteins of Borrelia burgdorferi

The three genospecies Borrelia burgdorferi, Borrelia garinii, and Borrelia afzelii, all causative agents of Lyme disease, differ in their susceptibili ties to human complement-mediated lysis. We recently reported that serum re sistance of borrelias correlates largely with their ability to bind the hum an complement regulators FHL-1/ reconectin and factor H. To date, two compl ement regulator-acquiring-proteins (CRASP-1 and CRASP-2) have been identifi ed in serum-resistant B. afzelii isolates (P. Kraiczy, C. Skerka, NI. Kirsc hfink, V. Brade, and P. F. Zipfel, Eur. J. Immunol. 31:1674-1684, 2001). He re, we present a comprehensive study of the CRASPs detectable in both serum -resistant and intermediate serum-sensitive B. afzelii and B. burgdorferi i solates. These CRASPs were designated according to the genospecies either a s BaCRASPs, when derived from B. afzelii, or as BbCRASPs, for proteins iden tified in B. burgdorferi isolates. Each borrelial isolate expresses distinc t CRASPs that can be differentiated by their mobility and binding phenotype s. A detailed comparison reveals overlapping and even identical binding pro files for BaCRASP-1 (27.5 kDa), BbCRASP-1 (25.9 kDa), and BbCRASP-2 (23.2 k Da), which bind FHL-1/reconectin strongly and interact weakly with factor I I. In contrast, two B. afzelii proteins (BaCRASP-4 [19.2 kDa] and BaCRASP-5 [22.5 kDa]) and three B. burgdorferi proteins (BbCRASP-3 [19.8 kDa], BbCRA SP-4 [18.5 kDa], and BbCRASP-5 [17.7 kDa]) bind factor II but not FHL-1/rec onectin. Most CRASPs bind both human immune regulators at their C-terminal ends. Temperature-dependent upregulation of CRASPs (BaCRASP-1, BaCRASP-2, a nd BaCRASP-5) is detected in low-passage borrelias cultured at 33 or 37 deg reesC compared with those cultured at 20 degreesC. The characterization of the individual CRASPs on the molecular level is expected to identify new vi rulence factors and potential vaccine candidates.