Functional Characterization of LcpA, a Surface-Exposed Protein ofLeptospiraspp. That Binds the Human Complement Regulator C4BP

Abstract

We have previously shown that pathogenic leptospiral strains are able to bind C4b binding protein (C4BP). Surface-bound C4BP retains its cofactor activity, indicating that acquisition of this complement regulator may contribute to leptospiral serum resistance. In the present study, the abilities of seven recombinant putative leptospiral outer membrane proteins to interact with C4BP were evaluated. The protein encoded by LIC11947 interacted with this human complement regulator in a dose-dependent manner. The cofactor activity of C4BP bound to immobilized recombinant LIC11947 (rLIC11947) was confirmed by detecting factor I-mediated cleavage of C4b. rLIC11947 was therefore named LcpA (for leptospiral complement regulator-acquiring protein A). LcpA was shown to be an outer membrane protein by using immunoelectron microscopy, cell surface proteolysis, and Triton X-114 fractionation. The gene coding for LcpA is conserved among pathogenic leptospiral strains. This is the first characterization of a Leptospira surface protein that binds to the human complement regulator C4BP in a manner that allows this important regulator to control complement system activation mediated either by the classical pathway or by the lectin pathway. This newly identified protein may play a role in immune evasion by Leptospira spp. and may therefore represent a target for the development of a human vaccine against leptospirosis.

OmpL1 Is an Extracellular Matrix- and Plasminogen-Interacting Protein of Leptospira spp

“…Based on this assumption, we decided to evaluate whether OmpL1 can also adhere to human PLG in vitro. In addition, we investigated whether the recombinant protein can also bind factor H, human complement, and C4bp, as previously reported for other recombinant proteins (4,5,11,16,71). Our data show that OmpL1 binds to human PLG (P Ͻ 0.01), while no or a very low level of reactivity was detected with the other components and the control proteins (Fig.…”

Characterization of Three Novel Adhesins of Leptospira interrogans

“…62 Leptospiral binding proteins to C4BP, factor H, and factor H-like have been identified in Leptospira. 17,18,46,[63][64][65][66] We report that Lsa23 is a novel C4BP and factor H binding protein of Leptospira, although with the ligand affinity for factor H binding protein seems to be low.…”

Pathogenic Leptospira Species Acquire Factor H and Vitronectin via the Surface Protein LcpA

“…The virulence of L. interrogans serovar Kennewicki strain Fromm is maintained by iterative passages in hamsters. Bacteria were cultured at 29°C under aerobic conditions as previously described (8).…”

“…Identification of specific host ligands and definition of the mechanism of complement inactivation have been accomplished for certain leptospiral outer membrane proteins present only in pathogenic species. In a previous work, we characterized a 20-kDa surface protein of Leptospira, LcpA (leptospiral complement regulator-acquiring protein A), which has been shown to interact with C4BP, a negative regulator of the classical and lectin pathways of complement (8). The cofactor activity of C4BP bound to immobilized LcpA was confirmed by detecting the C4d fragment obtained by factor I (FI)-mediated cleavage of C4b.…”

“…LcpA was shown to be an outer membrane protein by use of immunoelectron microscopy, Triton X-114 fractionation, and cell surface proteolysis. The lcpA gene is conserved among pathogenic Leptospira spp., and the protein is expressed by serum-resistant and serum-intermediate strains (8). Moreover, it has been reported that LcpA is expressed during the course of human infection (9).…”