Complement Regulator-Acquiring Surface Protein 1 Imparts Resistance to Human Serum in Borrelia burgdorferi

• Published in: The Journal of immunology (1950) 2005-09, Vol.175 (5), p.3299-3308
• Main Authors: Brooks, Chad S, Vuppala, Santosh R, Jett, Amy M, Alitalo, Antti, Meri, Seppo, Akins, Darrin R
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - physiology; Blood Bactericidal Activity; Blood Proteins - metabolism; Borrelia burgdorferi - immunology; Complement C3b Inactivator Proteins; Complement Factor H - metabolism; Humans; Membrane Proteins - physiology; Protein Transport
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.175.5.3299

Factor H and factor H-like protein 1 (FH/FHL-1) are soluble serum proteins that negatively regulate the alternative pathway of complement. It is now well recognized that many pathogenic bacteria, including Borrelia burgdorferi, bind FH/FHL-1 on their cell surface to evade complement-mediated destruction during infection. Recently, it was suggested that B. burgdorferi open reading frame bbA68, known as complement regulator-acquiring surface protein 1 (CRASP-1), encodes the major FH/FHL-1-binding protein of B. burgdorferi. However, because several other proteins have been identified on the surface of B. burgdorferi that also can bind FH/FHL-1, it is presently unclear what role CRASP-1 plays in serum resistance. To examine the contribution of CRASP-1 in serum resistance, we generated a B. burgdorferi mutant that does not express CRASP-1. The B. burgdorferi CRASP-1 mutant, designated B31cF-CRASP-1, was found to be as susceptible to human serum as a wild-type strain of Borrelia garinii 50 known to be sensitive to human serum. To further examine the role of CRASP-1 in serum resistance, we also created a shuttle vector that expresses CRASP-1 from the native B. burgdorferi gene, which was designated pKFSS-1::CRASP-1. When the pKFSS-1::CRASP-1 construct was transformed into the B. burgdorferi B31cF-CRASP-1 mutant, wild-type levels of serum resistance were restored. Additionally, when pKFSS-1::CRASP-1 was transformed into the serum-sensitive B. garinii 50 isolate, human serum resistance was imparted on this strain to a level indistinguishable from wild-type B. burgdorferi. The combined data led us to conclude that CRASP-1 expression is necessary for B. burgdorferi to resist killing by human serum.