Complement Resistance of Borrelia burgdorferi Correlates with the Expression of BbCRASP-1, a Novel Linear Plasmid-encoded Surface Protein That Interacts with Human Factor H and FHL-1 and Is Unrelated to Erp Proteins

Peter Kraiczy,Jens Hellwage,Christine Skerka,Heiko Becker,Michael Kirschfink,Markus M Simon,Volker Brade,Peter F Zipfel,Reinhard Wallich

doi:10.1074/jbc.m308343200

Abstract

The etiologic agent of Lyme disease, Borrelia burgdorferi, is capable of circumventing the immune defense of a variety of potential vertebrate hosts. Previous work has shown that interaction of host-derived complement regulators, factor H and factor H-like protein 1 (FHL-1), with up to five complement regulator-acquiring surface proteins (CRASPs) expressed by resistant B. burgdorferi sensu lato isolates conferred complement resistance. In addition expression of CRASP-1 is directly correlated with complement resistance of Borrelia species. This work describes the functional characterization of BbCRASP-1 as the dominant factor H and FHL-1-binding protein of B. burgdorferi. The corresponding gene, zs7.a68, is located on the linear plasmid lp54 and is different from factor H-binding Erp proteins that are encoded by genes localized on circular plasmids (cp32). Deletion mutants of BbCRASP-1 were generated, and a high affinity binding site for factor H and FHL-1 was mapped to the C terminus of BbCRASP-1. Similarly, the predominant binding site of factor H and FHL-1 was localized to the short consensus repeat 7. Factor H and FHL-1 maintain their cofactor activity for factor I-mediated C3b inactivation when bound to BbCRASP-1, and factor H is up to 6-fold more efficient in mediating C3b conversion than FHL-1. In conclusion, BbCRASP-1 (i). binds the host complement regulators factor H and FHL-1 with high affinity, (ii). is the key molecule of the complement resistance of spirochetes, and (iii). is distinct from the Erp protein family. Thus, BbCRASP-1 most likely contributes to persistence of B. burgdorferi and to pathogenesis of Lyme disease.

Highlights

The etiologic agent of Lyme disease, Borrelia burgdorferi, is capable of circumventing the immune defense of a variety of potential vertebrate hosts
Identification and Cloning of the Gene Encoding BbCRASP-1 of B. burgdorferi Strain ZS7—In order to identify B. burgdorferi complement regulator-acquiring surface proteins (CRASPs)-1, a genomic DNA expression library derived from B. burgdorferi strain ZS7 was screened for factor H and FHL1-binding clones
BbCRASP-1 is encoded by a linear plasmid lp54 localized gene and distinct from members of the factor H-binding Erp protein family

Summary

Introduction

The etiologic agent of Lyme disease, Borrelia burgdorferi, is capable of circumventing the immune defense of a variety of potential vertebrate hosts. Because of the complex enzootic cycle of B. burgdorferi in nature including diverse environments such as arthropod vectors and a variety of vertebrate hosts, spirochetes have developed strategies to survive in both vector and reservoir hosts These include their ability (i) to evade an immune defense by differential expression of polymorphic outer surface proteins [2], (ii) to sequester into immune privileged sites [3, 4], and (iii) to adapt to new environmental stimuli [5]. An increasing number of microorganisms pathogenic to humans, including B. burgdorferi [11,12,13], Neisseria gonorrhoeae [14], Neisseria meningitidis [15], Streptococcus pyogenes (16 – 19), and Streptococcus pneumoniae [20], resist complementmediated killing by coating their surfaces with host-derived fluid phase negative complement regulators of the alternative pathway, factor H, and/or factor H-like protein 1 (FHL-1).

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