The multifunctional LigB adhesin binds homeostatic proteins with potential roles in cutaneous infection by pathogenic Leptospira interrogans.

Henry A Choy,Mathieu Picardeau,Melissa M Kelley,Albert I Ko,David A Haake,James Matsunaga,Julio Croda,Jane T Babbitt,Paulo Ho

doi:10.1371/journal.pone.0016879

Abstract

Leptospirosis is a potentially fatal zoonotic disease in humans and animals caused by pathogenic spirochetes, such as Leptospira interrogans. The mode of transmission is commonly limited to the exposure of mucous membrane or damaged skin to water contaminated by leptospires shed in the urine of carriers, such as rats. Infection occurs during seasonal flooding of impoverished tropical urban habitats with large rat populations, but also during recreational activity in open water, suggesting it is very efficient. LigA and LigB are surface localized proteins in pathogenic Leptospira strains with properties that could facilitate the infection of damaged skin. Their expression is rapidly induced by the increase in osmolarity encountered by leptospires upon transition from water to host. In addition, the immunoglobulin-like repeats of the Lig proteins bind proteins that mediate attachment to host tissue, such as fibronectin, fibrinogen, collagens, laminin, and elastin, some of which are important in cutaneous wound healing and repair. Hemostasis is critical in a fresh injury, where fibrinogen from damaged vasculature mediates coagulation. We show that fibrinogen binding by recombinant LigB inhibits fibrin formation, which could aid leptospiral entry into the circulation, dissemination, and further infection by impairing healing. LigB also binds fibroblast fibronectin and type III collagen, two proteins prevalent in wound repair, thus potentially enhancing leptospiral adhesion to skin openings. LigA or LigB expression by transformation of a nonpathogenic saprophyte, L. biflexa, enhances bacterial adhesion to fibrinogen. Our results suggest that by binding homeostatic proteins found in cutaneous wounds, LigB could facilitate leptospirosis transmission. Both fibronectin and fibrinogen binding have been mapped to an overlapping domain in LigB comprising repeats 9–11, with repeat 11 possibly enhancing binding by a conformational effect. Leptospirosis patient antibodies react with the LigB domain, suggesting applications in diagnosis and vaccines that are currently limited by the strain-specific leptospiral lipopolysaccharide coats.

Highlights

Leptospirosis is a potentially fatal zoonotic disease in humans and animals caused by pathogenic spirochetes, such as Leptospira interrogans [1,2,3]
We previously showed that both host proteins are ligands for LigA and LigB, two outer membrane proteins in pathogenic Leptospira strains that are members of a superfamily of bacterial proteins containing immunoglobulin-like repeats with adhesive properties [14,15]
In order to further demonstrate the importance of Lig as a leptospiral adhesin, we show that the genetic transformation of nonpathogenic L. biflexa with ligA or ligB from L. interrogans increases the adherence of the surrogate to immobilized fibronectin

Summary

Introduction

Leptospirosis is a potentially fatal zoonotic disease in humans and animals caused by pathogenic spirochetes, such as Leptospira interrogans [1,2,3]. Fibronectin and fibrinogen are major constituents in the circulation where they could potentially interact with the leptospires in their hematogenous dissemination to distal tissue. Both plasma fibronectin and fibrinogen can be deposited in extracellular matrix or become associated with host cells. We previously showed that both host proteins are ligands for LigA and LigB, two outer membrane proteins in pathogenic Leptospira strains that are members of a superfamily of bacterial proteins containing immunoglobulin-like repeats with adhesive properties [14,15]. The osmotic induction of Lig enhances binding to fibronectin and fibrinogen along with other host proteins in an in vitro model of leptospiral adhesion to extracellular matrix [15]. Recombinant LigB has higher affinity than LigA for host proteins [15], and the current study focuses on the potential role of the former during cutaneous infection early in leptospirosis

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Conclusion