Pathogenic leptospires have the ability to survive and disseminate to multiple organs after penetrating the host. Several pathogens, including spirochetes, have been shown to express surface proteins that interact with the extracellular matrix (ECM). This adhesin-mediated binding process seems to be a crucial step in the colonization of host tissues. This study examined the interaction of putative leptospiral outer membrane proteins with laminin, collagen type I, collagen type IV, cellular fibronectin, and plasma fibronectin. Six predicted coding sequences selected from the Leptospira interrogans serovar Copenhageni genome were cloned, and proteins were expressed, purified by metal affinity chromatography, and characterized by circular dichroism spectroscopy. Their capacity to mediate attachment to ECM components was evaluated by binding assays. We have identified a leptospiral protein encoded by LIC12906, named Lsa24 (leptospiral surface adhesin; 24 kDa) that binds strongly to laminin. Attachment of Lsa24 to laminin was specific, dose dependent, and saturable. Laminin oxidation by sodium metaperiodate reduced the protein-laminin interaction in a concentration-dependent manner, indicating that laminin sugar moieties are crucial for this interaction. Triton X-114-solubilized extract of L. interrogans and phase partitioning showed that Lsa24 was exclusively in the detergent phase, indicating that it is a component of the leptospiral membrane. Moreover, Lsa24 partially inhibited leptospiral adherence to immobilized laminin. This newly identified membrane protein may play a role in mediating adhesion of L. interrogans to the host. To our knowledge, this is the first leptospiral adhesin with laminin-binding properties reported to date.

LipL32 is the major leptospiral outer membrane lipoprotein expressed during infection and is the immu-

Background: It has been well documented over past decades that interaction of pathogens with the extracellular matrix (ECM) plays a primary role in host cell attachment and invasion. Adherence to host tissues is mediated by surface-exposed proteins expressed by the microorganisms during infection. The mechanisms by which pathogenic leptospires invade and colonize the host remain poorly understood since few virulence factors contributing to the pathogenesis of the disease have been identified. Whole-genome sequencing analysis of L. interrogans allowed identification of a repertoire of putative leptospiral surface proteins.

Leptospirosis is a spirochetal zoonotic disease of global distribution with a high incidence in tropical regions. In the last 15 years it has been recognized as an important emerging infectious disease due to the occurrence of large outbreaks in warm-climate countries and, occasionally, in temperate regions. Pathogenic leptospires efficiently colonize target organs after penetrating the host. Their invasiveness is attributed to the ability to multiply in blood, adhere to host cells, and penetrate into tissues. Therefore, they must be able to evade the innate host defense. The main purpose of the present study was to evaluate how several Leptospira strains evade the protective function of the complement system. The serum resistance of six Leptospira strains was analyzed. We demonstrate that the pathogenic strain isolated from infected hamsters avoids serum bactericidal activity more efficiently than the culture-attenuated or the nonpathogenic Leptospira strains. Moreover, both the alternative and the classical pathways of complement seem to be responsible for the killing of leptospires. Serum-resistant and serum-intermediate strains are able to bind C4BP, whereas the serumsensitive strain Patoc I is not. Surface-bound C4BP promotes factor I-mediated cleavage of C4b. Accordingly, we found that pathogenic strains displayed reduced deposition of the late complement components C5 to C9 upon exposure to serum. We conclude that binding of C4BP contributes to leptospiral serum resistance against host complement.

BackgroundLeptospirosis is considered a re-emerging infectious disease caused by pathogenic spirochaetes of the genus Leptospira. Pathogenic leptospires have the ability to survive and disseminate to multiple organs after penetrating the host. Leptospires were shown to express surface proteins that interact with the extracellular matrix (ECM) and to plasminogen (PLG). This study examined the interaction of two putative leptospiral proteins with laminin, collagen Type I, collagen Type IV, cellular fibronectin, plasma fibronectin, PLG, factor H and C4bp.ResultsWe show that two leptospiral proteins encoded by LIC11834 and LIC12253 genes interact with laminin in a dose - dependent and saturable mode, with dissociation equilibrium constants (KD) of 367.5 and 415.4 nM, respectively. These proteins were named Lsa33 and Lsa25 (Leptospiral surface adhesin) for LIC11834 and LIC12253, respectively. Metaperiodate - treated laminin reduced Lsa25 - laminin interaction, suggesting that sugar moieties of this ligand participate in this interaction. The Lsa33 is also PLG - binding receptor, with a KD of 23.53 nM, capable of generating plasmin in the presence of an activator. Although in a weak manner, both proteins interact with C4bp, a regulator of complement classical route. In silico analysis together with proteinase K and immunoflorescence data suggest that these proteins might be surface exposed. Moreover, the recombinant proteins partially inhibited leptospiral adherence to immobilized laminin and PLG.ConclusionsWe believe that these multifunctional proteins have the potential to participate in the interaction of leptospires to hosts by mediating adhesion and by helping the bacteria to escape the immune system and to overcome tissue barriers. To our knowledge, Lsa33 is the first leptospiral protein described to date with the capability of binding laminin, PLG and C4bp in vitro.

Leptospirosis is an infectious disease of public health importance. To successfully colonize the host, pathogens have evolved multiple strategies to escape the complement system. Here we demonstrate that the culture supernatant of pathogenic but not saprophytic Leptospira inhibit the three complement pathways. We showed that the proteolytic activity in the supernatants of pathogenic strains targets the central complement molecule C3 and specific proteins from each pathway, such as factor B, C2, and C4b. The proteases cleaved α and β chains of C3 and work in synergy with host regulators to inactivate C3b. Proteolytic activity was inhibited by 1,10-phenanthroline, suggesting the participation of metalloproteases. A recombinant leptospiral metalloprotease from the thermolysin family cleaved C3 in serum and could be one of the proteases responsible for the supernatant activity. We conclude that pathogenic leptospiral proteases can deactivate immune effector molecules and represent potential targets to the development of new therapies in leptospirosis.

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The elongation factor Tu (EF-Tu), an abundant bacterial protein involved in protein synthesis, has been shown to display moonlighting activities. Known to perform more than one function at different times or in different places, it is found in several subcellular locations in a single organism, and may serve as a virulence factor in a range of important human pathogens. Here we demonstrate that Leptospira EF-Tu is surface-exposed and performs additional roles as a cell-surface receptor for host plasma proteins. It binds plasminogen in a dose-dependent manner, and lysine residues are critical for this interaction. Bound plasminogen is converted to active plasmin, which, in turn, is able to cleave the natural substrates C3b and fibrinogen. Leptospira EF-Tu also acquires the complement regulator Factor H (FH). FH bound to immobilized EF-Tu displays cofactor activity, mediating C3b degradation by Factor I (FI). In this manner, EF-Tu may contribute to leptospiral tissue invasion and complement inactivation. To our knowledge, this is the first description of a leptospiral protein exhibiting moonlighting activities.